Journal of Colloid And Interface Science (v.318, #2)
SERRS and visible extinction spectroscopy of copper chlorophyllin on silver colloids as a function of pH
by Paul G. House; Cheryl S. Schnitzer (pp. 145-151).
A study of sodium copper chlorophyllin adsorbed on silver colloids (CuChl/Ag) is conducted using surface-enhanced resonance Raman scattering (SERRS) and visible extinction spectroscopy to examine how the system changes as a function of pH. Initially at basic pH, SERRS signal is not detected even though CuChl is adsorbed onto the silver surface and deprotonated. Upon decreasing the solution pH slightly, colloidal aggregation is induced, evidenced by the broadening of the visible extinction spectra. The larger aggregates possess a surface plasmon that is in resonance with the laser excitation frequency (633-nm) and SERRS signal is detected. As the acid protonates CuChl, the overall negatively-charged surface approaches neutrality which induces more aggregation. Complete protonation of CuChl by pH 4.6 results in colloidal precipitation. However, when aggregation is halted about pH 5, adding NaOH( aq) to the system maintains the extent of aggregation and an intense SERRS signal is detected at basic pH.
Keywords: Copper chlorophyllin; SERRS; Raman spectroscopy; Visible extinction spectroscopy; pH; Titration curve; Adsorption; Silver colloid; Colloidal aggregation
Reversibility in particle deposition: The effect of mobile fraction of particles on monolayer structures
by Panu Danwanichakul (pp. 152-159).
In this work, the degree of reversibility in particle deposition was introduced by surface diffusion. The effect of mobile fraction of triangular-well particles on the surface among the immobile ones was explored by varying number of particles added at a time in modified sequential quenching model. It was found that at low temperatures, as the number of added mobile particles increased, the structures was composed of more compact clusters connecting to one another, thereby, decreasing the percolating density while at high temperatures, the structures are more disordered and the final structures were independent on the deposition flux, leading to the unchanged percolating density.The fraction of mobile particles among the immobile ones, ranging fromdρ∗=0.0025 to 0.1000 was observed to affect the monolayer structures and corresponding percolating densities at low temperatures.
Keywords: Random sequential adsorption; Irreversible adsorption; Sequential deposition; Equilibrium adsorption; Monte Carlo simulation; Surface diffusion; Monolayer structure
Adsorption of Pb2+, Zn2+, and Cd2+ from waters by amorphous titanium phosphate
by Kun Jia; Bingcai Pan; Qingrui Zhang; Weiming Zhang; Peijuan Jiang; Changhong Hong; Bingjun Pan; Quanxing Zhang (pp. 160-166).
In the current study, amorphous titanium phosphate (TiP) was prepared as an adsorbent for heavy metals from waters. Uptake of Pb2+, Zn2+, and Cd2+ onto TiP was assayed by batch tests; a polystyrene–sulfonic acid exchanger D-001 was selected for comparison and Ca2+ was chosen as a competing cation due to its ubiquitous occurrence in waters. The pH-titration curve of TiP implied that uptake of heavy metals onto TiP is essentially an ion-exchange process. Compared to D-001, TiP exhibits more preferable adsorption toward Pb2+ over Zn2+ and Cd2+ even in the presence of Ca2+ at different levels. FT-IR analysis of the TiP samples laden with heavy metals indicated that the uptake of Zn2+ and Cd2+ ions onto TiP is mainly driven by electrostatic interaction, while that of Pb2+ ions is possibly dependent upon inner-sphere complex formation, except for the electrostatic interaction. Moreover, uptake of heavy metals onto TiP approaches equilibrium quickly and the exhausted TiP particles could be readily regenerated by HCl solution.Adsorption of three heavy metals onto amorphous titanium phosphate was examined by batch tests and the corresponding mechanism was further explored by FT-IR analysis.
Keywords: Titanium phosphate; Heavy metals; Adsorption; Mechanism
Petroleum resins adsorption onto quartz sand: Near infrared (NIR) spectroscopy study
by Roman M. Balabin; Rustem Z. Syunyaev (pp. 167-174).
In this paper we have tried to evaluate adsorption parameters of petroleum resins. Near infrared (NIR) spectroscopy is applied for resins bulk concentration evaluation during adsorption process. NIR experimental scheme and parameters are provided. NIR spectra range of 9000–13,000 cm−1 is chosen. Quartz sand (0.2–0.8 mm fraction) is used as adsorbent; benzene is used as solvent. Different approaches of “NIR spectra–resins concentration” calibration model building are discussed. Partial least squares (PLS) regression method is used. Langmuir model is chosen for experimental data fitting. Combined usage of kinetic and isothermic data gives us ability to evaluate the maximal adsorbed mass density, the equilibrium constant of adsorption, and the rate constants of adsorption (and desorption). The rate constants of resins adsorption and desorption are found to be concentration independent.Kinetics and thermodynamics of petroleum resins adsorption measured by near infrared (NIR) spectroscopy method. Adsorption rate constant and Gibbs energy of adsorption are evaluated.
Keywords: Petroleum resins; Adsorption; Near infrared (NIR) spectroscopy; Partial least squares (PLS) regression; Quartz sand; Langmuir model
Adsorption behavior of statherin and a statherin peptide onto hydroxyapatite and silica surfaces by in situ ellipsometry
by Olga Santos; Jelena Kosoric; Mark Prichard Hector; Paul Anderson; Liselott Lindh (pp. 175-182).
The salivary protein statherin is known to adsorb selectively onto hydroxyapatite (HA), which constitutes the main mineral of the tooth enamel. This adsorption is believed to be crucial for its function as an inhibitor of primary (spontaneous) and secondary (crystal growth) precipitation of calcium phosphate salts present in saliva. A fragment corresponding to the first 21 N-terminus amino acids of statherin (StN21) was previously found to reduce the rate of demineralization of HA. Therefore, the interfacial properties of this peptide and statherin onto silica, hydrophobized silica and HA discs was studied by in situ ellipsometry. Their reversibility induced by dilution and elutability induced by buffer and sodium dodecyl sulfate (SDS) was also determined. The results revealed that statherin adsorbed at a greater extent onto the HA as compared to StN21, suggesting that the hydrogen bonding between the uncharged polar residues at the C-terminal region of statherin and HA contributes to its adsorption. However, on both silica surfaces the peptide adsorption appeared to proceed in a similar way. Onto the hydrophobized silica the adsorption of both peptides was suggested to occur either via multilayer formation or adsorption of aggregates from solution, while onto the hydrophilic silica adsorption of peptide aggregates from solution was the suggested mechanism. Further, both peptides were observed to be strongly adsorbed onto HA, even after SDS treatment, in comparison to the layers adsorbed onto hydrophobized silica. Both peptide layers were found to be weakly adsorbed onto the hydrophilic silica surface as they were totally removed by buffer dilution.
Keywords: Adsorption; Ellipsometry; Statherin; Hydroxyapatite; Silica; Elution; Surfactants
Detection of hydrophobic microdomains in anionic polyelectrolytes with tris-(4,7-diphenyl-1,10-phenanthroline)3Cr(III)
by Paulina Cañete; Hernán E. Ríos; Víctor Vargas; Silvia Ronco; Mauricio Isaacs; Marcela D. Urzúa (pp. 183-187).
This paper describes the changes in the luminescent properties of the tris-(4,7-diphenyl-1,10-phenanthroline)3Cr(III), [Cr(dip)3]3+ complex in an aqueous solution of three polyelectrolytes containing cyclohexyl, phenyl or 1-naphthyl groups in the side chain. When the polyelectrolytes form hydrophobic microdomains the luminescence of [Cr(dip)3]3+ is affected. The luminescence increases in the presence of cyclohexyl groups in the side chains, but decreases in the presence of phenyl and naphthyl groups (in that order). This fact can be explained in terms of a reductive quenching mechanism between the complex and the aromatic groups. Indeed, experiments performed with the complex and the alcohols corresponding to the functional groups, i.e., cyclohexanol, phenol, and naphthol, also show the same behavior, confirming the interaction with the functional groups and not other components of the polyelectrolyte. The luminescent properties of the [Cr(dip)3]3+ complex allow the detection of hydrophobic microdomains arising from the host–guest interaction. Moreover, the complex is able to distinguish between a nonaromatic hydrophobic microdomain and an aromatic one.The luminescence of a chromium(III) polypyridyl complex is strongly affected when it is in solution of three different anionic polyelectrolytes. These changes are useful to distinguish between nonaromatic and aromatic hydrophobic microdomains in the polyelectrolytes.
Keywords: Chromium complexes; Anionic polyelectrolytes; Hydrophobic microdomains; Luminescence
Molecular dynamics simulations of structural features and diffusion properties of fullerene-in-water suspensions
by Kuan-Chuan Fang; Cheng-I. Weng (pp. 188-194).
This study performs molecular dynamics (MD) simulations to investigate the structural features and diffusion properties of fullerene-in-water suspensions. The numerical results reveal that an organized structure of liquid water is formed close to the surface of the fullerene molecule, thereby changing the solid/liquid interfacial structure. The organized structure formation becomes more pronounced as the fullerene size is reduced. This observation implies that a transition zone exists between the organized liquid water layers and the random distribution region. Furthermore, the results indicate that the structural stability of fullerene-in-water suspensions improves as the fullerene volume fraction increases, but is insensitive to changes in the fullerene size. Finally, the simulation results reveal that the diffusion coefficient of the water molecules varies as a linear function of the fullerene loading, but is independent of the fullerene size.The reduced density (ρlocal/ρbulk) of water molecules implies the formation of two shell-like water layers in the proximity of the fullerene surface.
Keywords: Structural feature; Diffusion coefficient; Fullerene-in-water suspensions; Molecular dynamics (MD) simulation
Easy deposition of Ag onto polystyrene beads for developing surface-enhanced-Raman-scattering-based molecular sensors
by Kwan Kim; Hyang Bong Lee; Hyoung Kun Park; Kuan Soo Shin (pp. 195-201).
We describe a very simple electroless plating method that can be used to prepare Ag-coated polystyrene beads. Robust Ag nanostructures are reproducibly fabricated by soaking polystyrene beads in ethanolic solutions of AgNO3 and butylamine. When the molar ratio of butylamine to AgNO3 is far below 1.0, distinct nanosized Ag particles are formed on the polystyrene beads, but by increasing the amount of butylamine, network-like Ag nanostructures are formed that possess very broad UV/vis absorption characteristics extending from the near-UV to near-infrared regions. In conformity with the UV/vis absorption characteristics, the Ag-deposited polystyrene beads were highly efficient surface-enhanced Raman scattering (SERS) substrates, with an enhancement factor estimated using 4-aminobenzenethiol (4-ABT) as a model adsorbate to be larger than1.1×106. On the basis of the nature of the SERS peaks of 4-ABT, those Ag-deposited polystyrene beads were confirmed, after attaching biotin groups over 4-ABT, to selectively recognize streptavidin molecules down to concentrations of 10−11 g mL−1 (i.e., ∼0.2 pM). Since a number of different molecules can be used as SERS-marker molecules (such as 4-ABT), multiple bioassays are readily accomplished via SERS after attaching appropriate host or guest molecules onto them.Ag-coated polystyrene (PS) beads, easily prepared by electroless deposition method, are highly efficient SERS substrate usable as a core material of SERS-based molecular sensors; the last cartoon illustrates the interaction of biotinylated beads with other biotinylated substrates by the mediation of streptavidin molecules labeled as “X.”
Keywords: Polystyrene beads; Silvering; SERS; 4-Aminobenzenethiol; Biosensor
Modified fractal model and rheological properties of colloidal networks
by Dongming Tang; Alejandro G. Marangoni (pp. 202-209).
The scaling relationship between the storage modulus (G′) and the volume fraction of solids ( Φ) in fat crystal networks has been explained by the fractal model developed by our group. However, many experimental results and simulation studies suggest that the stress distribution within a colloidal network is dramatically heterogeneous, which means that a small part of the network carries most of the stress, while the other part of the network does not contribute much to the elastic properties of the system. This concept was introduced into a modified fractal model. The volume fraction of solids term ( Φ) in the original fractal model was replaced byΦe, the effective volume fraction of solids, in the modified fractal model, which represents the volume fraction of stress-carrying solids. A proposed expression forΦe is given and a modified expression for the scaling relationship betweenG′ and Φ is obtained. The modified fractal model fits the experiment data well and successfully explains the sometimes observed nonlinear log–log behavior between the storage modulus of colloidal networks and their volume fraction of solids.The scaling relationship between the storage modulus and the volume fraction of solids in fat crystal colloidal networks is explained by a modified fractal model which incorporates the concept of heterogeneity in the distribution of stress within the colloidal network.
Keywords: Colloidal network; Rheology; Structure; Fractal; Modeling
First successful design of semi-IPN hydrogel–silver nanocomposites: A facile approach for antibacterial application
by P.S.K. Murthy; Y. Murali Mohan; K. Varaprasad; B. Sreedhar; K. Mohana Raju (pp. 217-224).
Semi-IPN hydrogels in which poly(vinyl pyrrolidone) (PVP) chains were physically dispersed throughout poly(acrylamide) (PAM) gel networks were synthesized. These semi-IPN hydrogel networks can act as excellent nanoreactors for producing and stabilizing metal nanoparticles. The current methodology allows us to entrap metal nanoparticles throughout hydrogel networks via PVP chains. An optimized semi-IPN hydrogel formulation was found to produce silver nanoparticles, ca. 3–5 nm. The synthesized semi-IPN hydrogel–silver nanocomposites were fully characterized by using UV–vis, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The developed semi-IPN hydrogel–silver nanocomposite (SHSNC) was evaluated for preliminary antibacterial applications.We demonstrated for the first time that for semi-IPN hydrogel silver nanocomposites the silver nanoparticles are highly distributed throughout the gel networks. For this, a number of different IPN hydrogels were prepared by varying the concentration of interpenetrate polymer, i.e., poly(vinyl pyrrolidone), cross-linker, initiator, and activators. It was found that highly cross-linked semi-IPN gel networks allow the silver nanoparticles to grew and alignment of particles inside the gel networks showed 5–10 nm in diameter. The developed semi-IPN hydrogel silver nanocomposite exhibited excellent antibacterial characteristics. Figure: Silver nanoparticles grew inside the semi-IPN hydrogel networks and TEM image of silver nanoparticles.
Keywords: Hydrogel network; Composite hydrogel; Antibacterial activity; Silver nanoparticles
Salt-induced protein phase transitions in drying drops
by Tatiana Yakhno (pp. 225-230).
Protein phase transitions in drying sessile drops of protein–salt–water colloidal systems were studied by means of optical and atom-force microscopy. The following sequence of events was observed during drop drying: attachment of a drop to a glass support; redistribution of colloidal phase due to hydrodynamic centrifugal stream; protein ring formation around the edge; formation of protein spatial structures inside a protein ring that pass into gel in the middle of the drop; salt crystallization in the shrinking gel. It was assumed that rapid drying of a protein ring over the circle of high colloidal volume fraction and low strength of interparticle attraction leads to formation of colloidal glass, whereas gel forms only in the middle of the drop at very low protein volume fraction and strong attraction between the particles. Before gelation, colloidal particles form fractal clusters. In dried drops of salt-free protein solutions, no visual protein structures were observed. Structural evolution of protein in sessile drying drops of protein–salt aqueous colloidal solutions is discussed on the basis of experimental data.A cause–effect chain of salt-induced protein phase transitions in drying drops is proposed.
Keywords: Protein phase transitions; Drying sessile drops; Colloidal stability; Spatial protein structures
Preparation, characterization, and photocatalytic activity of sulfate-modified titania for degradation of methyl orange under visible light
by K.M. Parida; N. Sahu; N.R. Biswal; B. Naik; A.C. Pradhan (pp. 231-237).
Hydrated titania was prepared by a sol–gel method, taking tetraisopropyl orthotitanate as starting material, and then promoted with different weight percentages of sulfate by an incipient wetness impregnation method. The materials were characterized by various advanced techniques such as PXRD, BET surface area, N2 adsorption–desorption measurements, FTIR, and SEM. Analytical results demonstrated that TiO2 is mesoporous in nature, and sulfate modification could inhibit the phase transformation and enhance the thermal stability of TiO2. It was also found that sulfate modification could reduce the crystallite size and increase the specific surface area of the catalysts. The degradation of methyl orange under solar radiation was investigated to evaluate the photocatalytic activity of these materials. Effects of different parameters such as pH of the solution, amount of catalyst, additives, and kinetics were investigated. At 2.5 wt% sulfate loading, the average percentage of degradation of methyl orange was nearly two times than that of neat TiO2. The photocatalytic degradation followed first-order kinetics.Modification of SO2−4 on TiO2 increases the photocatalytic reaction; 61% MO degradation was found in the case of 2.5 wt% SO2−4/TiO2 against 33% in the case of neat TiO2.
Keywords: Sulfate-modified titania; Photocatalyst; Crystallite size; Methyl orange
Kinetics of gold nanoparticle aggregation: Experiments and modeling
by Taehoon Kim; Chang-Ha Lee; Sang-Woo Joo; Kangtaek Lee (pp. 238-243).
We investigate the aggregation kinetics of gold nanoparticles using both experimental techniques (i.e., quasi-elastic light scattering, UV–visible spectroscopy, and transmission electron microscopy) and mathematical modeling (i.e., constant-number Monte Carlo). Aggregation of gold nanoparticles is induced by replacing the surface citrate groups with benzyl mercaptan. We show that the experimental results can be well described by the model in which interparticle interactions are described by the classical DLVO theory. We find that final gold nanoparticle aggregates have a fractal structure with a mass fractal dimension of 2.1–2.2. Aggregation of approximately 11 initial gold nanoparticles appears to be responsible for the initial color change of suspension. This kinetic study can be used to predict the time required for the initial color change of a gold nanoparticle suspension and should provide insights into the design and optimization of colorimetric sensors that utilize aggregation of gold nanoparticles.
Keywords: Gold; Nanoparticle; Aggregation; Kinetics; Fractal structure; Colorimetric sensor
Tuning aggregation of microemulsion droplets and silica nanoparticles using solvent mixtures
by Alireza Salabat; Julian Eastoe; Kevin J. Mutch; Rico F. Tabor (pp. 244-251).
The effect of solvent on stability of water-in-oil microemulsions has been studied with AOT (sodium bis(2-ethylhexyl)sulfosuccinate) and different solvent mixtures of n-heptane, toluene and dodecane. Dynamic light scattering DLS was used to monitor the apparent diffusion coefficientDA and effective microemulsion droplet diameter on changing composition of the solvent. Interdroplet attractive interactions, as indicated by variations inDA, can be tuned by formulation of appropriate solvent mixtures using heptane, toluene, and dodecane. In extreme cases, solvent mixtures can be used to induce phase transitions in the microemulsions. Aggregation and stability of model AOT-stabilized silica nanoparticles in different solvents were also investigated to explore further these solvent effects. For both systems the state of aggregation can be correlated with the effective molecular volume of the solventVmoleff mixture.Microemulsion phase separation with increasing dodecane mole fraction in solvent mixtures of heptane and dodecane at 298 K.
Keywords: Microemulsion; AOT; Aggregation; DLS; Silica nanoparticles
Viscous solvent colloidal system for direct visualization of suspension structure, dynamics and rheology
by Michael Kogan; Clare J. Dibble; Reginald E. Rogers; Michael J. Solomon (pp. 252-263).
We introduce a model colloid system comprised of particles dispersed in a viscous solvent that can be applied to 3D direct visualization studies of suspension structure, dynamics and rheology. The colloids are poly(methyl methacrylate) (PMMA) spheres sterically stabilized by a copolymer of poly(diphenyl–dimethyl) (DPDM) siloxane that matches the refractive index of PMMA. The monodisperse particles, synthesized with mean diameter varying from 0.7 to 1.1 μm, are stably dispersed in a DPDM siloxane solvent, with viscosity varying from 2.2 to 4.3 Pa s at 20 °C. As opposed to other classes of PMMA colloids dispersed in organic solvents, this system displays minimal charge interactions. At room temperature, pair potential interactions (measured by extrapolation of pair correlation functions to infinite dilution) are well modeled by a generalized Lennard-Jonesα–2α potential (α=10) with dimensionless interaction energy,ε/kBT=0.6. We use the DPDM–PMMA colloidal system in conjunction with confocal microscopy studies to measure: (i) the radial distribution function in 3D at dilute concentrations and (ii) the colloid self-diffusivity in 3D at dilute concentrations. Both measurements, neither previously reported in uncharged systems, are facilitated by the slow, viscous dynamics of the system. We also show that the viscosity and particle size of the system are such that the high-volume fraction shear thickening transition can be accessed at shear rates amenable to direct visualization.
Keywords: Colloid synthesis; PMMA; Shear thickening; Confocal microscopy; Pair potential interactions
Methods for functionalization of microsized polystyrene beads with titania nanoparticles for cathodic electrophoretic deposition
by S. Radice; P. Kern; H. Dietsch; S. Mischler; J. Michler (pp. 264-270).
Functionalization of colloidal particles based on the use of polyelectrolytes and heterocoagulation was combined with electrophoretic deposition (EPD), with the aim of depositing titania–polystyrene (TiO2–PS) composite particles on Ti6Al4V substrates. The composite particles were obtained by heterocoagulation of TiO2 nanoparticles on the surface of monosized polystyrene beads of 4.6 μm in diameter. Two alternative methods were developed for the preparation of the TiO2–PS suspensions in organic fluids for cathodic electrodeposition. The first method was carried out in alkaline aqueous medium with the use of polyelectrolytes and intermediate control measurements of zeta potential, conductivity, and pH; the second one was carried out directly in the organic solvent used for EPD, typically isopropanol. Examples of deposits obtained by EPD in both suspensions and a comparative analysis between the two methods are presented.Negatively charged colloidal polystyrene beads of 4.6 μm in diameter were functionalized with positively charged TiO2 nanoparticles and deposited cataphoretically on Ti6Al4V substrates. Two procedures for the preparation of the polystyrene–TiO2 composite particles based on heterocoagulation were developed and compared.
Keywords: Heterocoagulation; Coating; Macroporosity; Template; Polyelectrolyte
Molecular features of the air/carbonate solution interface
by Hao Du; Jin Liu; Orhan Ozdemir; Anh V. Nguyen; Jan D. Miller (pp. 271-277).
The nature of the air/carbonate solution interface is considered with respect to water structure by sum-frequency vibrational spectroscopy (SFVS) and molecular dynamics simulations (MDS). Results from this study provide further understating regarding previous observations that the surface tensions of structure making sodium carbonate solutions have been shown to be significantly greater than the surface tensions of structure breaking bicarbonate solutions at equivalent concentrations. This difference in surface tension and its variation with salt concentration is related to the organization of water and ions at the air/solution interface. Spectral results from SFVS show at equivalent concentrations that, for the carbonate solution, the strong water structure signal of 3200 cm−1 at the air/carbonate solution interface is increased by a factor of 4 when compared to the same signal for the air/bicarbonate solution interface, which spectrum is weaker than the spectrum for the air/water interface in the absence of salt. These results from SFVS are explained by the results from MDS which show that in the case of carbonate solutions the structure making carbonate ions are excluded from the interfacial water region which region is extended in depth. On the other hand, in the case of bicarbonate solutions, the bicarbonate ions are accommodated in the interfacial water region and there is no evidence of an increase in the extent of water structure. These SFVS experimental and MD simulation results provide further information to understand interfacial phenomena of soluble salts at the molecular level.The SFVS spectra for pure water, saturated sodium bicarbonate solution and saturated sodium carbonate solution in the OH stretching region at the air/liquid interfaces.
Keywords: Interfacial water structure; Carbonate solution; Sum-frequency vibrational spectroscopy; Molecular dynamic simulation; Surface tension
Evolution of the passive film and organic constituents at the surface of stainless steel immersed in fresh water
by J. Landoulsi; M.J. Genet; C. Richard; K. El Kirat; S. Pulvin; P.G. Rouxhet (pp. 278-289).
The evolution of the surface of a conventional stainless steel (AISI 316L) immersed in aqueous medium simulating fresh water (pH ∼8) was studied using XPS and AFM. A detailed analysis of XPS spectra allowed a distinction to be made between oxygen of organic and inorganic nature. During the first 48 h, the main changes concern the inorganic phase: the oxygen concentration in the passive layer increases, owing both to oxidation of metal elements, including conversion of FeII to FeIII, and to hydration; the molar ratio of oxidized species Feox/Crox decreases slightly; the formation of colloidal particles, presumably made of ferric hydroxide, is observed by AFM. After longer periods of immersion, the Feox/Crox is higher, while the coating of colloidal particles reaches a full surface coverage. The amount of organic compounds increases further and the XPS spectra reveal the accumulation of polysaccharides and proteins, which indicate that these organic compounds are of biological origin.XPS and AFM study of stainless steel surface upon immersion in fresh water: formation of colloidal particles presumably made of ferric hydroxide, adsorption of organic compounds of biological origin.
Keywords: Stainless steel; Passive film; XPS; AFM; Iron oxides; Organic contamination; Biofouling
Measurement of the surface potential of individual crystal planes of hematite
by Nikola Kallay; Tajana Preočanin (pp. 290-295).
A device for measuring surface potentials of individual crystal planes was constructed. The surface potentials of the (012), (10−2), (113), and (11−3) crystal planes of hematite were measured as a function of pH at different sodium nitrate concentrations. Results of measurement enabled differentiation between the planes, showing agreement with the surface potentials obtained with a single-crystal hematite electrode. At low ionic strength there was no significant difference in potential between the crystal planes, whereas at relatively high ionic strength the difference was noticeable. In the absence of counterion association, but also in the case of their symmetric association taking place, point of zero potential (pHpzp) coincides with other zero points, i.e., with the isolectric point (pHiep) and the point of zero charge (pHpzc). If the counterion affinities toward association are not equal, the pHpzp is shifted in the same directions as the pHpzc. The shift in the point of zero potential to the basic region was more pronounced for the (11−3) plane than for the (10−2) one, indicating a higher affinity of anions for association with oppositely charged surface groups compared to cations. It was demonstrated that measurements of surface potentials of individual crystal planes could help to better understand the equilibrium at solid/liquid interfaces.Surface potential of individual crystal planes of hematite measured as a function of pH at different sodium nitrate concentrations.
Keywords: Surface potential; Surface complexation model; Hematite; Crystal planes; Single-crystal electrodes
Voltammetric behavior of cefdinir in solubilized system
by Rajeev Jain; Ashish Dwivedi; Ritesh Mishra (pp. 296-301).
The voltammetric behavior of cefdinir has been studied in different surfactant media viz. anionic, neutral, and cationic surfactants over the pH range 2.5–12 in phosphate buffer (0.2 M). Addition of cationic surfactant (citrimide) to the cefdinir containing electrolyte enhanced the reduction current signal while anionic surfactant (sodium lauryl) and neutral surfactant (Tween-20) showed an opposite effect. The reduction process was irreversible over the entire pH range studied (2.5–12). The mechanism of reduction has been postulated on the basis of controlled potential electrolysis, coulometry and spectral analysis. An analytical method with adequate precision and accuracy was developed for the determination of cefdinir in linear concentration range2×10−4–1×10−5molL−1 with detection limit0.3×10−6molL−1. The analysis of cefdinir in its pharmaceutical formulation resulted in mean recoveries of 99 and 98% for both the reduction peaks.A rapid and sensitive voltammetric method was developed for the qualitative and quantitative analysis of cefdinir in cationic surfactant using phosphate buffer. The peak current is found to be linear over the concentration range2×10−4 to1×10−5molL−1 and the lower detection limit (LOD) is found to be0.3×10−6molL−1.
Keywords: Cefdinir; Cetrimide; Pharmaceutical formulation; DPP; CV
Mechanism for hydrotalcite decomposition: A controlled rate thermal analysis study
by Veronika Vágvölgyi; Sara J. Palmer; János Kristóf; Ray L. Frost; Erzsébet Horváth (pp. 302-308).
The mechanism for the decomposition of hydrotalcite remains unsolved. Controlled rate thermal analysis enables this decomposition pathway to be explored. Hydrotalcites containing carbonate, vanadate and molybdate were prepared by coprecipitation. The resulting materials were characterised by XRD, simultaneous TG–DTG–DTA and controlled rate thermal analysis (CRTA) to determine the stability and thermal decomposition pathway of the synthesised hydrotalcites. For the carbonate intercalated hydrotalcite dehydration takes place in three steps two of which are quasi-isothermal and one non-isothermal. Dehydroxylation and decarbonation occur separately over the 235–330 and 330–370 °C temperature range. A second non-isothermal decarbonation step is observed in the 371–541 °C range. In comparison the mixed carbonate–vanadate and carbonate–molybdate hydrotalcites show two dehydration steps and the dehydroxylation and decarbonation occur simultaneously. The observation of three dehydration steps is used to support the model of water molecules in three structurally distinct environments in the hydrotalcite interlayer. CRTA technology provides a mechanism for the decomposition of hydrotalcites.
Keywords: Hydrotalcite; Carbonate; Molybdate; Vanadate; Pyroaurite; Thermogravimetry; CRTA
Synthesis, amino-functionalization of mesoporous silica and its adsorption of Cr(VI)
by Jiansheng Li; Xiaoyu Miao; Yanxia Hao; Jiangyan Zhao; Xiuyun Sun; Lianjun Wang (pp. 309-314).
Mesoporous silica materials with a centered rectangular symmetry (cmm) have been synthesized through a facile direct-templating method using tetraethylorthosilicate (TEOS) and amphiphilic block co-polymers Pluronic P123 under acidic conditions. The amino groups have been grafted to as-synthesized mesoporous silica by [1-(2-amino-ethyl)-3-aminopropyl]trimethoxysilane (AAPTS). Thus obtained amino-functionalized mesoporous silica (denoted as NN-silica) was used for sequestration of Cr(VI) from aqueous solution. After sequestration of Cr(VI), the sample was denoted as Cr(VI)-silica. The parent mesoporous silica, NN-silica and Cr(VI)-silica were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and N2 adsorption–desorption isotherms. XRD and TEM results confirm that the structure of these samples is centered rectangular symmetry (cmm). N2 adsorption–desorption isotherms show that there is a remarkable decrease in surface area and pore volume for NN-silica (SBET=54.5m2g−1,VP=0.09cm3g−1) and Cr(VI)-silica (SBET=53.2m2g−1,VP=0.07cm3g−1) compared to the parent mesoporous silica (SBET=444.0m2g−1,VP=0.71cm3g−1). The BJH desorption average diameter of NN-silica, Cr(VI)-silica and the parent mesoporous silica is 4.40 nm, 4.07 nm and 5.11 nm, respectively. The results reveal the channels of as-synthesized mesoporous silica are essentially grafted with abundant amino groups and loaded with Cr(VI). The adsorption experiment results show that the functionalized mesoporous silica materials possess an increased Cr(VI) adsorption capacity and the maximum Cr(VI) loadings at 25, 35 and 45 °C can reach 2.28, 2.86 and 3.32 mmol/g, respectively.Mesoporous silica materials with a centered rectangular symmetry (cmm) have been synthesized and functionalized by grafting of amino group. The obtained materials exhibit improved Cr(VI) adsorption capacity. The ordered mesoporous structures are visible for all samples.
Keywords: Mesoporous silica; Amino groups; Functionalization; Cr(VI) adsorption
Mesoporous Fe2O3 microspheres: Rapid and effective enrichment of phosphopeptides for MALDI-TOF MS analysis
by Lu Han; Zhe Shan; Dehong Chen; Xijuan Yu; Pengyuan Yang; Bo Tu; Dongyuan Zhao (pp. 315-321).
Mesoporous Fe2O3 microspheres have been successfully synthesized by the polymerization (urea and formaldehyde)-induced ferric hydroxide colloid aggregation. The urea-formaldehyde resin was removed by calcination in air. The obtained mesoporous Fe2O3 materials have spherical morphology with uniform particle size of∼3.0μm and porous surface with large inter-particle pores of∼48.0nm. The surface area is as large as∼33.3m2/g and the pore volume is 0.31 cm3/g. The mesoporous Fe2O3 microspheres were used for the enrichment of phosphopeptides for the first time, in which high sensitivity, selectivity and capacity of specifically enriched phosphopeptides were achieved under a mild condition in a relative short time. After enriched from tryptic digest products of β-casein by the novel mesoporous Fe2O3 microspheres, phosphopeptides can be selectively detected with high intensity in MALDI-TOF mass spectrometry. Elimination of “shadow effect” was observed by using mesoporous Fe2O3 microspheres, and the detectable limitation is5×10−10M. This material is also effective for enrichment of phosphopeptides from the complex tryptic digests of commercial phosphoprotein casein, with much more phosphorylated sites (26 in 27 of total) and higher signal/noise ratio in the MALDI-TOF mass spectrometry, compared to commercial Fe2O3 nanoparticles. It shows a great potential application in the field of rapid and effective isolation of phosphopeptides.Mesoporous Fe2O3 microspheres have been successfully synthesized by the polymerization (urea and formaldehyde)-induced ferric hydroxide colloid aggregation.
Keywords: Ferric oxide; Mesoporous materials; Mass spectrometry; Phosphopeptide; Specific enrichment
Water evaporation rates across hydrophobic acid monolayers at equilibrium spreading pressure
by Minami Tsuji; Hiromichi Nakahara; Yoshikiyo Moroi; Osamu Shibata (pp. 322-330).
The effect of alkanoic acid [CH3(CH2) n−2COOH; HC n] and perfluoroalkanoic acid [CF3(CF2) n−2COOH; FC n] monolayers on the water evaporation rate was investigated by thermogravimetry tracing the decrease in amount of water with time. The evaporation rate from the surface covered by a monolayer was measured as a function of temperature and hydrophobic chain length of the acids, where the monolayer was under an equilibrium spreading pressure. From thermal behavior of the crystallized acids, their solid states are C-type in crystalline state over the temperature range from 298.2 to 323.2 K. The dry air was flowed through a furnace tube of a thermogravimetry apparatus at the flow rate of 80 mL min−1, where the evaporation rate becomes almost constant irrespective of the flow rate. The temperature dependence of the evaporation rate was analyzed kinetically to evaluate the activation energy and thermodynamics values for the activated complex, which demonstrated that these values were almost the same for both alkanoic acids and perfluoroalkanoic acids, although the effect of perfluoroalkanoic acids on the evaporation rate was smaller than that of corresponding hydrogenated fatty acids. The difference in the evaporation rate between FC n and HC n was examined by atomic force microscopy (AFM), Brewster angle microscopy (BAM), surface potential (Δ V) at equilibrium spreading pressure, and Langmuir curve (π–A isotherm), and their results were consistent and supported the difference.
Keywords: Fluorinated amphiphiles; Perfluoroalkanoic acids; Evaporation rate of water; Thermogravimetry (TG); Differential scanning calorimetry (DSC); Equilibrium spreading pressure (ESP); Atomic force microscopy (AFM)
Co-electrospun SiO2 hollow nanostructured fibers with hierarchical walls
by Sihui Zhan; Dairong Chen; Xiuling Jiao (pp. 331-336).
SiO2 hollow nanostructured fibers with hierarchical walls have been fabricated by the sol–gel combined two-capillary spinneret co-electrospinning technique using triblock copolymer as the porous directing agent. The as-prepared SiO2 hollow nanostructured fibers were as long as 10 cm with the outer diameter of 400–600 nm and shell thickness of 50–200 nm, and their walls contained the random mesopores with the size of 6.6 nm and the micropores with size of 0.6 nm based on the N2 absorption–desorption isotherm.SiO2 hollow nanostructured fibers with hierarchical meso/microporous walls have been fabricated by the sol–gel combined two-capillary spinneret co-electrospinning technique.
Keywords: SiO; 2; Mesoporous; Microporous; Hollow fibers; Electrospinning; Sol–gel processing
Study of assembly of arachidic acid/LDHs hybrid films containing photoactive dyes
by Jun Wang; Xuemei Ren; Xusheng Feng; Shangying Liu; Dejun Sun (pp. 337-347).
Hybrid monolayers formed with an floating arachidic acid (AA) anions monolayer binding with a densely packed layered double hydroxides (LDHs) monolayer at an air/LDHs suspension interface has been studied by π– A isotherms and TEM images. An ordered multilayer film of AA/LDHs has been fabricated by Langmuir–Blodgett technique on various substrates. The photoactive dyes (methyl orange, MO, and Congo red, CR) can be incorporated into the galleries of LDHs in the AA/LDHs hybrid LB film by an ion intercalation method. The results of FTIR and UV–vis absorption spectra can approve the formation of AA/LDHs/dyes composite films. In addition, UV–vis absorption spectra and LAXRD analyses also provide evidence for the good vertical uniformity and stable layered periodic structure of AA/LDHs/dyes films. More interestingly, it was found that the dye molecules intercalated can be induced by a positively charged LDHs sheet to align in a special orientation and form different aggregates: MO molecules form sandwich H-type aggregates, while CR molecules form head-to-tail J-type aggregates. On the basis of these data, a possible model of the AA/LDHs/dyes composite films was proposed. Also, the dye molecules incorporated into AA/LDHs films exhibit excellent configuration stability under the irradiation of UV light because the LDHs matrix offers a more rigid and constrained environment for them.The arrangement models of the dye molecules (methyl orange, MO, and Congo red, CR) intercalated into the gallery of the LDHs in a repeated unit of AA/LDHs hybrid films.
Keywords: Layered double hydroxides; Photoactive dyes; Langmuir–Blodgett technique; Intercalation reaction; Films
Adhesion and anti-adhesion of viscous fluids on solid surfaces—A study of ink transfer mechanism in waterless offset printing
by Wei Shen; Yu Mao; Gerard Murray; Junfei Tian (pp. 348-357).
The transfer of a liquid under dynamic conditions onto a solid surface relies on wetting/adhesion under transient external forces. We found the phenomena associated with forced wetting and dewetting could not be explained by thermodynamic approaches which are based on surface energy and work of adhesion. This is because these approaches do not take account of the dynamic nature of the forced wetting and dewetting. This study uses ink transfer in waterless offset printing as an example to present a new understanding of adhesion and anti-adhesion of a liquid to a solid surface under dynamic conditions. We focus on the adhesion strength, instead of work of adhesion, at the ink–plate interface and experimentally quantified ink adhesion forces on the image and non-image areas of the printing plate. Based on adhesion force measurements we proposed that the formation of a weak boundary layer and/or the softening the non-image area due to solvent swelling are likely to be the mechanisms that causes ink refusal on the non-image area. AFM images are presented to show changes of the non-image surface before and after contacting with ink.A weak (or soft) boundary layer on the non-image area rejects ink adhesion to this area. Printing force measurement shows the forces of ink transfer on the image area and ink refusal on the non-image area.
Keywords: Adhesion; Anti-adhesion; Forced wetting; Ink refusal mechanisms; Waterless offset printing
Effect of ionic surfactants on drainage and equilibrium thickness of emulsion films
by Stoyan I. Karakashev; Emil D. Manev; Roumen Tsekov; Anh V. Nguyen (pp. 358-364).
This paper presents new theoretical and experimental results that quantify the role of surfactant adsorption and the related interfacial tension changes and interfacial forces in the emulsion film drainage and equilibrium. The experimental results were obtained with plane-parallel microscopic films from aqueous sodium dodecyl sulphate solutions formed between two toluene droplets using an improved micro-interferometric technique. The comparison between the theory and the experimental data show that the emulsion film drainage and equilibrium are controlled by the DLVO interfacial forces. The effect of interfacial viscosity and interfacial tension gradient (the Marangoni number) on the film drainage is also significant.Unlike foam films, the effect of ionic surfactant on the drainage of the toluene–water–toluene films stabilized by 0, 1, 10 and 30 μM SDS was found to be satisfactorily described by the DLVO surface forces—no extension of the DLVO theory to include hydrophobic or hydrophilic interaction is required. Interfacial viscosity and interfacial tension gradient are also important.
Keywords: Emulsion films; DLVO forces; Surfactants; Kinetics of film thinning
Flexible transparent conducting single-wall carbon nanotube film with network bridging method
by Young Il Song; Cheol-Min Yang; Dong Young Kim; Hirofumi Kanoh; Katsumi Kaneko (pp. 365-371).
We fabricated random network films of highly pure single-wall carbon nanotubes (SWCNTs) on flexible polyethylene terephthalate substrate by dip- and spray-coatings and their combination method for application to flexible transparent conducting films (TCFs). The dip-coating treatment was a more efficient method for fabricating the SWCNT-TCFs of high electrical conductivity without drastic drop in the optical transmittance, compared to the spray-coating one. This should be primarily due to more loose contact in intertube and interbundle junctions of the spray-coated SWCNT networks. Although the electrical conductivity of the SWCNT-TCFs was dramatically enhanced as increasing the number of dipping times, the dip-coating treatment with a large number of dipping times considerably reduced the transmittance without corresponding improvement in the electrical conductivity, indicating the patch-wise coating of the SWCNTs. On the other hand, the combination of the spray- and dip-coatings gave a supplementary effect for formation of a highly transparent film of better electrical conductivity. For SWCNT-TCF coated with 100 dipping times, an additional spray-coating dramatically decreased the sheet resistance from 1300 to 340 Ω/square, which is accompanied by slight reduction of the transmittance from 88 to 80%. Therefore, the post spray-coating can efficiently bridge the patch-wise SWCNT networks produced by the successive dip-coating.Additional spray-coating treatment on dip-coated single-wall carbon nanotube-based transparent conducting film can efficiently bridge the quasi one-dimensional conducting pathways, resulting in enhancement of electrical conductivity without drastic drop of optical transmittance.
Keywords: Single-wall carbon nanotubes; Transparent conducting films; Dip coating; Spray coating
Tuning the hydrophobic properties of silica particles by surface silanization using mixed self-assembled monolayers
by Sneha A. Kulkarni; Satishchandra B. Ogale; Kunjukrishanan P. Vijayamohanan (pp. 372-379).
Here we describe a novel method of preparing hydrophobic silica particles (100–150 nm; water contact angle of dropcasted film ranging from 60° to 168°) by surface functionalization using different alkyltrichlorosilanes. During their preparation, the molecular surface roughness is also concurrently engineered facilitating a change in both the surface chemical composition and the geometrical microstructure to generate hierarchical structures. The water contact angle has been measured on drop-cast film surface. The enhancement in the water contact angle on 3D (curved) SAMs in comparison to that on 2D (planar) surface is discussed using the Cassie–Baxter equation. These silica particles can be utilized for many potential applications including selective adsorbents and catalysts, chromatographic supports and separators in microfluidic devices.
Keywords: Silica particles; Alkyltrichlorosilane; Silanization; Superhydrophobicity
Structuring bubbles and foams in gelatine solutions within a circular microchannel device
by O. Skurtys; J.M. Aguilera (pp. 380-388).
A flow-focusing device with circular cross-section to produce monodispersed air bubbles and foams in several gelatine solutions is presented. Four flow regimes were studied by varying the gas pressure: dripping, bi-disperse bubbly, bubbly and foam flows. Bubble formation at the flow-focusing exit is discussed in detail and compared with that in rectangular microchannels. The bubble volume was shown to depend on the viscosity of the gelatine solution but not on the surface tension. For the bubbly flow, the frequency of bubble formation in this geometry was similar to that found in rectangular microchannels. For the foam flow the frequency was independent of the pressure. Study in the outlet microchannel for the bubbly and foam flows showed that the gas flow followed a power law with the applied pressure. Finally, the viscous resistance was measured and a pressure drop law was determined for each regime.The bubble volumeVb multiplied by the liquid pressure dropQgelμgelLoutDout4 is plotted against the gas pressurePg for 5 concentrations of gelatine solutions. Four flow regimes were distinguished: dripping, bi-disperse bubbly, bubbly and foam flows.
Keywords: Bubbles; Microbubbles; Microstructure; Foams; Microfluidics; Gelatine
Micellization and synergistic interaction of binary surfactant mixtures based on sodium nonylphenol polyoxyethylene ether sulfate
by Zhong-Xiu Chen; Shao-Ping Deng; Xiao-Kui Li (pp. 389-396).
Mixed micelle formation and synergistic interactions of binary surfactant combinations of sodium nonylphenol polyoxyethylene ether sulfate (NPES) with typical surfactants such as sodium dodecyl sulfate (SDS), Triton X-100 (TX100), cetyl trimethyl ammonium bromide (CTAB), and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) at 25 °C in the presence of NaCl have been investigated. The critical micelle concentration of the binary mixtures has been quantitatively estimated by steady-state fluorescence measurements. The micellar characteristics such as composition, activity coefficients, and mutual interaction parameters have been estimated following different theoretical treatments. Investigation on the micellization and synergistic interaction of NPES with four kinds of surfactants showed that the behavior of the binary mixture deviated from the ideal state. The analysis revealed that the interaction parameter values ( β) varied with variation of solvent composition. Besides the strong electrostatic attraction between the oppositely charged surfactant NPES–CTAB mixture, the interaction between NPES and SDS also showed far more deviation from ideal behavior than that of TX100 and AOT. The reason for the synergism is also discussed and the results show that an ionic and a nonionic surfactant character existed concurrently in NPES due to the combination of a sulfate group and polyoxyethylene as a hydrophilic moiety. Zeta potential and diffusion coefficient measurements of micelles confirmed the synergistic interaction between the binary surfactants.Besides the strong electrostatic attraction between oppositely charged surfactant NPES–CTAB mixtures, the interaction between NPES and SDS also showed far more deviation from ideal behavior than those of TX100 and AOT. The results show that ionic and nonionic surfactant characteristics existed concurrently in NPES due to the combination of sulfate group and polyoxyethylene as hydrophilic moiety.
Keywords: Sodium nonylphenol polyoxyethylene ether sulfate; SDS; CTAB; Synergistic interactions; Fluorescence measurements; Zeta potential; Diffusion coefficients
A novel low-molecular-mass gelator with a redox active ferrocenyl group: Tuning gel formation by oxidation
by Jing Liu; Junlin Yan; Xuanwei Yuan; Kaiqiang Liu; Junxia Peng; Yu Fang (pp. 397-404).
A novel low-molecular-mass gelator containing a redox-active ferrocenyl group, cholesteryl glycinate ferrocenoylamide (CGF), was intentionally designed and prepared. It was demonstrated that the gelator gels 13 out of the 45 solvents tested. Scanning electron microscopy (SEM) measurements revealed that the gelator self-assembled into different supramolecular network structures in different gels. Chemical oxidation of the ferrocenyl residue resulted in phase transition of the gel from gel state to solution state. FTIR and1H NMR spectroscopy studies revealed that hydrogen bonding between the gelator molecules in the gel was one of the main driving forces for the formation of the gels.A novel low-molecular-mass organic gelator containing a ferrocenyl group was prepared, and it was found that chemical oxidation of the ferrocenyl residue resulted in dissolution of a gel of ethyl acetate containing the gelator.
Keywords: Gelator; Ferrocene; Stimuli-responsive gels; Cholesterol
Ternary cubic phases containing ionic liquid
by Zhongni Wang; Wu Zhou; Ganzuo Li (pp. 405-410).
The phase diagram of 1-butyl-3-methylimidazolium tetrafluoroborate (bmim-BF4) in aqueous solutions of oleyl polyoxyethylene (20) ether (C18:1E20) was determined at 25 °C by a combination of visual inspection and small-angle X-ray scattering (SAXS). The micellar cubicIm3m liquid crystalline phase found in the ternary system was investigated by means of SAXS and rheological techniques. The cubic samples show highly elastic gel-like properties indicated by their mechanical and discrete relaxation spectra. Moreover at a constant C18:1E20/bmim-BF4 ratio, with decreasing water content the network strength increases. The internal structure apparently becomes more stable, as indicated by an increase in the storage and loss moduli and a decrease in the lattice parameter α and interfacial area of per surfactantaS. Furthermore, investigations on the representative micellarIm3m cubic phases formed in a relatively hydrophobic ionic liquid bmim-PF6 with C18:1E20 and water ternary system (P1), a C18:1E20/water binary system (J1), and C18:1E20/water/bmim-BF4 system (B1) were made in comparison. It can be clearly seen that appreciably different mechanical spectra and relaxation spectra are shown by the cubic phases investigated. B1 exhibits a typical gel-like dynamic rheogram while P1 exhibits fluid-like viscoelastic properties to some extent, and J1 shows traits of the general Maxwell model. These differences are analyzed through SAXS data as the employment of ionic liquids and their different location in the cubic phases.Discrete relaxation spectra of the cubic liquid crystals at 25 °C for C18:1E20/water/bmim-BF4 (B1, B2, B3), C18:1E20/water/bmim-PF6 (P1), and C18:1E20/water (J1) systems.
Keywords: Cubic liquid crystal; Ionic liquid; Olyed surfactant
Structure and phase equilibria of mixtures of the complex salt hexadecyltrimethylammonium polymethacrylate, water and different oils
by Juliana Silva Bernardes; Watson Loh (pp. 411-420).
This work reports on phase diagrams for mixtures of a complex salt formed by a cationic surfactant and an oppositely charged polyelectrolyte, hexadecyltrimethylammonium polymethacrylate, in binary mixtures with water and in ternary mixtures containing water and organic solvents of different polarity (‘oils’): decanol, octanol, p-xylene and cyclohexane. The liquid crystalline structures formed were identified by small angle X-ray scattering measurements, which also provided information about changes in the size of the aggregates as a function of the system composition. These results are analysed in comparison with others previously reported [Bernardes et al., J. Phys. Chem. B 110 (2006) 10332–10340] for the analog complex formed with polyacrylate and, in general, reveal that the presence of an extra methylene group in the polymer chain does not produce significant changes in the complex phase diagrams nor in the structure of the liquid crystalline phases formed. Additionally, the obtained results confirm once more the approach used to analyze these kinds of systems formed by polymer and oppositely charged surfactant.This study reports phase diagrams and structures of mesophases formed by mixtures of a complex salt formed by a cationic surfactant and a polyanion, with water and different organic solvents.
Keywords: Phase equilibrium; Polyion–surfactant ion complex salt; Decanol; Octanol; p; -Xylene; Polymethacrylic acid; Hexadecyltrimethylammonium
Phosphatidylcholine embedded micellar systems: Enhanced permeability through rat skin
by Aviram Spernath; Abraham Aserin; Amnon C. Sintov; Nissim Garti (pp. 421-429).
Micellar and microemulsion systems are excellent potential vehicles for delivery of drugs because of their high solubilization capacity and improved transmembrane bioavailability. Mixtures of propylene glycol (PG) and nonionic surfactants with sodium diclofenac (DFC) were prepared in the presence of phosphatidylcholine (PC) as transmembrane transport enhancers. Fully dilutable systems with maximum DFC solubilization capacity (SC) at pH 7 are presented. It was demonstrated that the concentrates underwent phase transitions from reverse micelles to swollen reverse micelles and, via the bicontinuous transitional mesophase, into inverted O/W microstructures. The SC decreases as a function of dilution. DFC transdermal penetration using rat skin in vitro correlated with SC, water content, effect of phospholipid content, presence of an oil phase, and ethanol. Skin penetration from the inverted bicontinuous mesophase and the skin penetration from the O/W-like microstructure were higher than that measured from the W/O-like droplets, especially when the micellar system containing the nonionic surfactant, sugar ester L-1695, and hexaglycerol laurate. PC embedded within the micelle interface significantly increased the penetration flux across the skin compared to micellar systems without the embedded PC at their interface. Moreover, the combination of PC with HECO40 improved the permeation rate(P) and shortened the lag-time (TL).Solubilization capacity and the rat skin penetration of diclofenac solubilized in different micellar structure are presented. Enhance drug penetration was achieved by the incorporation of phosphatidylcholine into the micellar system without any phase separation.
Keywords: Microemulsions; Phosphatidylcholine; Diclofenac; Permeability; Transdermal drug delivery
Modulation of the adsorption properties at air–water interfaces of complexes of egg white ovalbumin with pectin by the dielectric constant
by Elena V. Kudryashova; Harmen H.J. de Jongh (pp. 430-439).
The possibility of modulating the mesoscopic properties of food colloidal systems by the dielectric constant is studied by determining the impact of small amounts of ethanol (10%) on the adsorption of egg white ovalbumin onto the air–water interface in the absence and presence of pectin. The adsorption kinetics was monitored using tensiometry. The addition of ethanol resulted in considerably slower adsorption of the protein onto the interface, and this effect was enhanced when the protein was in complex with the pectin. Time-resolved fluorescence measurements demonstrated that in the case of noncomplexed ovalbumin the addition of ethanol resulted in a more condensed protein surface layer where ovalbumin adopted a preferred orientation at the interface. In contrast, the effect of ethanol on the ovalbumin–pectin complex suggested a pronounced multipoint electrostatic interaction between protein and polyelectrolyte and the formation of a more rigid spatial arrangement within the complex, thereby leading to suppressed protein–protein interactions. From this work it is concluded that by the enhanced binding affinity between ovalbumin and pectin a strong effect on the adsorption properties of the protein can be accomplished. This work does therefore illustrate how solvent quality can be exploited effectively to enhance or suppress protein functional behavior in complex applications containing air–water interfaces.
Keywords: Air–water interface; Protein adsorption; Pectin; Solvent quality; Fluorescence; Surface tension
Adsorption and micellization behavior of novel gluconamide-type gemini surfactants
by Kenichi Sakai; Shin Umezawa; Mamoru Tamura; Yuichiro Takamatsu; Koji Tsuchiya; Kanjiro Torigoe; Takahiro Ohkubo; Tomokazu Yoshimura; Kunio Esumi; Hideki Sakai; Masahiko Abe (pp. 440-448).
The adsorption and micellization behavior of novel sugar-based gemini surfactants (N,N′-dialkyl-N,N′-digluconamide ethylenediamine, Glu( n)-2-Glu( n), where n is the hydrocarbon chain length of 8, 10 and 12) has been studied on the basis of static/dynamic surface tension, fluorescence, dynamic light scattering (DLS) and cryogenic transmission electron microscope (cryo-TEM) data. The static surface tension of the aqueous Glu( n)-2-Glu( n) solutions measured at the critical micelle concentration (cmc) is observed to be significantly lower than that of the corresponding monomeric surfactants. This suggests that the gemini surfactants, newly synthesized in the current study, are able to form a closely packed monolayer film at the air/aqueous solution interface. The greater ability in the molecular association is supported by the remarkably (approximately 100–200 times) lower cmc of the gemini surfactants compared with the corresponding monomeric ones. With a combination of the fluorescence and DLS data, a structural transformation of the Glu( n)-2-Glu( n) micelles is suggested to occur with an increase in the concentration. The cryo-TEM measurements clearly confirm the formation of worm-like micelles of Glu(12)-2-Glu(12) at the concentration well above the cmc.The adsorption and micellization behavior of novel sugar-based gemini surfactants has been studied on the basis of static/dynamic surface tension, fluorescence, DLS and cryo-TEM data.
Keywords: Sugar-based gemini surfactants; Adsorption; Worm-like micelles; Surface tension
Electrolyte effect on mixed micelle and interfacial properties of binary mixtures of cationic and nonionic surfactants
by Soheila Javadian; Hussein Gharibi; Zahra Bromand; Beheshteh Sohrabi (pp. 449-456).
In the present work, the adsorption behavior at the liquid–air interface and micellization characteristics of mixtures of cetyltrimethylammonium bromide (CTAB) and p-(1,1,3,3-tetramethylbutyl) polyoxyethylene (TritonX-100) in aqueous media containing different concentrations of NaBr were investigated by surface tension and potentiometry measurements. From plots of surface tension ( γ) as a function of solution composition and total surfactant concentration, we determined the critical micelle concentration (CMC), minimum surface tension at the CMC (γCMC), surface excess (Γmax), and mean molecular surface area (Amin). On the basis of regular solution theory, the compositions of the adsorbed film ( Z) and micelles (XM) were estimated, and then the interaction parameters in the micelles (βM) and in the adsorbed film phase (βσ) were calculated. For all mole fraction ratios, the results showed synergistically enhanced ability to form mixed micelles as well as surface tension reduction. Furthermore β was calculated by considering nonrandom mixing and head group size effects. It was observed that, for both the planar air/aqueous interface and micellar systems, the nonideality decreased as the amount of electrolyte in the aqueous medium was increased. This was attributed to a decrease of the surface charge density caused by increasing the concentration of bromide ions.Excess Gibbs free energy as a function of mole fraction of CTAB in the mixed micelle (X1∗) for CTAB/TritonX-100 mixtures atα=0.5 at different salt concentrations.
Keywords: CTAB; TritonX-100; Potentiometry; Surface tension; Electrolyte; Regular solution theory; Mixed micelle; Adsorption
Physicochemical influences on electrohydrodynamic transport in compressible packed beds of colloidal boehmite particles
by Bastian Schäfer; Hermann Nirschl (pp. 457-462).
Production and processing of colloidal particles require a deeper understanding of the surface charge of particles and the interaction of mass and charge transport in packed beds. The assessment of fundamental parameters is rather complex due to the additional influence of the particle charge on the structure of a packed bed. The combination of different measurement techniques (streaming potential and electroosmosis) allows for separating the effects, based on the postulation of a new method to quantify the ratio of surface conductance to liquid conductance. The purpose of this paper is to investigate the influence of pH value and compression on the electrohydrodynamic transport parameters.The combined interpretation of electroosmosis and streaming potential permits the assessment of different influences on the electrohydrodynamic transport and correct measurement of the zeta potential ζ in packed beds, which is consistent with electroacoustic measurements.
Keywords: Electrohydrodynamic transport; Electrokinetics; Electrostatics; Permeability; Colloidal particles
Deformation of a droplet in an electric field: Nonlinear transient response in perfect and leaky dielectric media
by Graeme Supeene; Charles R. Koch; Subir Bhattacharjee (pp. 463-476).
Deformation of a fluid drop, suspended in a second immiscible fluid, under the influence of an imposed electric field is a widely studied phenomenon. In this paper, the system is analyzed numerically to assess its dynamic behavior. The response of the system to a step change in the electric field is simulated for both perfect and leaky dielectric systems, exploring the influence of the fluid, interfacial, and electrical properties on the system dynamics. For the leaky dielectric case, the dynamic build up of the free charge at the interface, including the effects of convection along the interface due to electrohydrodynamic circulation, is investigated. The departure of the system from linear perturbation theory is explained using these dynamic simulations. The present simulations are compared with analytic solutions, as well as available experimental results, indicating that the predictions from the model are reliable even at considerably large deformations.Droplet deformation in an electric field for perfect and leaky dielectric systems. The deformation is prolate for perfect dielectrics, while it is oblate for leaky dielectrics. Different deformed shapes are obtained by varying the fluid properties in the leaky dielectric model.
Keywords: Droplet deformation; Electric field; Navier–Stokes equations; Finite element; Perfect dielectric; Leaky dielectric
Electrophoretic mobility does not always reflect the charge on an oil droplet
by V. Knecht; H.J. Risselada; A.E. Mark; S.J. Marrink (pp. 477-486).
Electrophoresis is widely used to determine the electrostatic potential of colloidal particles. Oil droplets in pure water show negative or positive electrophoretic mobilities depending on the pH. This is commonly attributed to the adsorption of hydroxyl or hydronium ions, resulting in a negative or positive surface charge, respectively. This explanation, however, is not in agreement with the difference in isoelectric point and point of zero charge observed in experiment. Here we present molecular dynamics simulations of oil droplets in water in the presence of an external electric field but in the absence of any ions. The simulations reproduce the negative sign and the order of magnitude of the oil droplet mobilities at the point of zero charge in experiment. The electrostatic potential in the oil with respect to the water phase, induced by anisotropic dipole orientation in the interface, is positive. Our results suggest that electrophoretic mobility does not always reflect the net charge or electrostatic potential of a suspended liquid droplet and, thus, the interpretation of electrophoresis in terms of purely continuum effects may need to be reevaluated.
Keywords: Electrophoresis; Electrokinetic phenomena; Zeta potential; Water structure; Molecular dynamics; Computer simulation
Formation of luminescent nanocomposite assemblies via electrostatic interaction
by Minglei Ji; Lan Jin; Jia Guo; Wuli Yang; Changchun Wang; Shoukuan Fu (pp. 487-495).
A novel luminescent nanocomposite assembly was prepared in aqueous solutions, via the electrostatic interaction between poly(ethylene glycol)- b-poly(N,N-dimethylaminoethyl methacrylate) (PEG- b-PDMAEMA) double hydrophilic block copolymer (DHBC) and thioglycolic acid (TGA)-stabilized CdTe quantum dots (QDs). By tuning the molar ratios of QDs to DHBC, the nanocomposite assemblies could be well controlled and the dimension of these regular spherical QDs/PEG- b-PDMAEMA assemblies ranged from 40 to 75 nm in aqueous media. As the periphery of QDs/PEG- b-PDMAEMA nanocomposite assembly was composed of PEG segments when the PDMAEMA blocks and QDs were immobilized inside the assembly, the cytotoxicity of the assembly was significantly reduced, compared with that of pure PEG- b-PDMAEMA and QDs. The nanocomposite assembly also exhibited superior stability in salt solutions and remained strongly photoluminescent even when free radicals existed. Thus, the QDs/PEG- b-PDMAEMA nanocomposite assembly is potentially useful for a number of applications in biolabeling and imaging.A novel luminescent nanocomposite assembly was prepared in aqueous solutions via the electrostatic interaction of PEG- b-PDMAEMA and QDs. The cytotoxicity of the nanocomposite assemblies was significantly reduced while the PDMAEMA blocks and QDs were immobilized inside the assembly.
Keywords: Nanocomposite assembly; Electrostatic interaction; Quantum dot
Self-assembly of a dialkylurea gelator in organic solvents in the presence of centrifugal and shearing forces
by Yun Xiong; Qingyao Liu; Hong Wang; Yajiang Yang (pp. 496-500).
A novel dialkylurea gelator, 1-methyl-2,4-bis(N′-octadecaneureido)benzene (designated as MBOB) was synthesized, which can turn some organic solvents into organogels at extremely low concentrations (<2 wt%). The1H NMR spectra of MBOB in solution (110 °C) and in the gel state (30 °C) indicate that intermolecular hydrogen bonding is the driving force for the self-assembly of MBOB. In the process of the self-assembly of MBOB, orientation of MBOB aggregates occurs under the influence of external fields, such as a centrifugal force and shearing force fields. The minimum gelation concentrations of MBOB in organic solvents under a centrifugal force field were significantly higher than those in the absence of a centrifugal force field, indicating a significant effect of the external field on the self-assembly of MBOB. Field emission scanning electron microscopy (FE-SEM) provided evidence for a significantly phase transition of the MBOB aggregates from an amorphous state in the absence of the external field to an oriented state under conditions of a centrifugal or shearing force during the gelation process. A self-assembled structure of MBOB is proposed based upon an X-ray diffraction (XRD) analysis and a molecular simulation. DSC analysis of the organogels indicates that the phase transition temperature increased from 58.5 °C in the absence of the external field to 63.3 °C under a centrifugal force field and 62.2 °C under a shearing force field. The enthalpy of the phase transition decreased from 3.1 J/g in the absence of an external field to 2.6 J/g under a centrifugal force field and 2.7 J/g under a shearing force field.A possible mechanism for a novel dialkylurea gelator assembly is proposed as above. In the absence of a force field, the fiber bundles of the gelator aggregates become spontaneously organized into entangled random networks. These fiber bundles show oriented alignments along the direction of force-induced.
Keywords: Dialkylurea gelator; Self-assembly; External field; Orientation
Surfactant-promoted formation of fractal and dendritic nanostructures of gold and silver at the organic–aqueous interface
by Ved Varun Agrawal; G.U. Kulkarni; C.N.R. Rao (pp. 501-506).
The effect of surfactants such as tetraoctylammoniumbromide (TOAB) and cetyltrimethylammoniumbromide (CTAB) on the type of nanostructures formed when gold ions present in the organic phase are reduced at the interface by hydrazine in the aqueous phase has been investigated. Extended fractal structures are formed at the liquid–liquid interface, the fractal structures themselves comprising cauliflower type units formed by gold nanorods. Accordingly, the nanostructures exhibit transverse and longitudinal plasmon adsorption bands in the 550 and 800 nm regions, respectively. Dendritic structures of silver are formed at the interface when Ag ions are reduced similarly in the presence of surfactants. The nanostructures consist of nanoparticles or nanorods with five-fold symmetry.Fractal and dendritic nanostructures of gold and silver are formed at the liquid–liquid interface in the presence of surfactants.
Keywords: Liquid–liquid; Fractal; Dendrites; Alloy; Nanostructures; Five-fold; Interface
On scale dependence in friction: Transition from intimate to monolayer-lubricated contact
by Dewei Xu; K. Ravi-Chandar; Kenneth M. Liechti (pp. 507-519).
Scale dependence in friction is studied in the present paper using the newly developed mesoscale friction tester (MFT). A transition in frictional shear strength from several hundreds of MPa to several tens of MPa was observed over a very limited range of contact radii (20–30 nm) in both ambient and dry environments. Thus, a single apparatus has been able to establish these two limits which are consistent with the values previously obtained from friction experiments using atomic force microscopy (AFM) and the surface force apparatus (SFA), respectively. Consequently, it is hypothesized here that a shear strength in the hundreds of MPa results from intimate contact (solid–solid) and a shear strength in the tens of MPa results from a monolayer-lubricated contact. Furthermore, both the probe size and the normal pressure govern the interfacial conditions in the contact zone and it is these conditions, rather than the nominal environment, which in turn determine the resulting shear strengths. A continuum analysis based on the Lifshitz theory for van der Waals interactions is used to explain the quantized shear strengths which were obtained from our experiments and previous AFM and SFA friction experiments. This quantized friction behavior [J.N. Israelachvili, P.M. McGuiggan, A.M. Homola, Science 240 (1988) 189] results from the discrete separation due to the different interfacial conditions that can arise between two sliding surfaces. The consistency between the analysis and the experimental results shows that this analysis is applicable for nonwear friction with single asperity contact.
Keywords: Friction; Scale dependence; Adhesion; Lifshitz theory; Intimate contact; Monolayer-lubricated contact
Evidence of direct crystal growth and presence of hollow microspheres in magnetite particles prepared by oxidation of Fe(OH)2
by Fernando Vereda; Benito Rodríguez-González; Juan de Vicente; Roque Hidalgo-Álvarez (pp. 520-524).
We provide new information relevant to the crystallinity and growth mechanism of magnetite particles that were fabricated following the method of Sugimoto and Matijević [J. Colloid Interface Sci. 74 (1980) 227]. These authors observed that in a small excess of Fe2+, particles grew by aggregation and recrystallization of smaller units, so that until now the resulting particles were thought to be polycrystalline. With the help of transmission electron microscopy (TEM) and selected area electron diffraction (SAED), we also detected the presence of monocrystalline particles, which are strong evidence of the occurrence of direct crystal growth. This growth mechanism seems to coexist with that of the aggregation of primary units proposed by Sugimoto and Matijević. Careful examination of electron microscopy micrographs also revealed the presence of many hollow polycrystalline microspheres.Magnetite samples grown by oxidation of Fe(OH)2 with KNO3 in excess Fe2+ contained a mixture of monocrystalline and polycrystalline particles. The presence of monocrystals suggests that direct crystal growth has a more predominant role than previously believed.
Keywords: Magnetite; Colloidal magnetite particles; Magnetite single crystals; Hollow particles; Crystal growth
Influence of n-alkyl acids on the percolative phenomena in AOT-based microemulsions
by A. Cid-Samamed; L. García-Río; D. Fernández-Gándara; J.C. Mejuto; J. Morales; M. Pérez-Lorenzo (pp. 525-529).
A study was carried out on the influence of the n-alkyl acid addition on the electric percolation of AOT/iso-octane/water microemulsions ([AOT] = 0.5 M and W= [H2O]/[AOT] = 22.2). The observed influence has been explained taking into account the organic nature of these molecules and, hence, their capacity of disturbing the structure of the AOT-film. For these reasons, relationships with their molecular structure (chain length) were analysed.The influence of fatty acids on the AOT/iso-octane/water microemulsions percolation has been explained taking into account the organic nature of these additives and their capacity of disturbing the AOT-film structure.
Keywords: Microemulsion; AOT; Electric percolation; Organic acids; Percolation threshold
Preparation of platinum-decorated porous graphite nanofibers, and their hydrogen storage behaviors
by Byung-Joo Kim; Young-Seak Lee; Soo-Jin Park (pp. 530-533).
In this work, the hydrogen storage behaviors of porous graphite nanofibers (GNFs) decorated by Pt nanoparticles were investigated. The Pt nanoparticles were introduced onto the GNF surfaces using a well-known chemical reduction method. We investigated the hydrogen storage capacity of the Pt-doped GNFs for the platinum content range of 1.3–7.5 mass%. The microstructure of the Pt/porous GNFs was characterized by X-ray diffraction and transmission electron microscopy. The hydrogen storage behaviors of the Pt/GNFs were studied using a PCT apparatus at 298 K and 10 MPa. It was found that amount of hydrogen stored increased with increasing Pt content to 3.4 mass%, and then decreased. This result indicates that the hydrogen storage capacity of porous carbons is based on both their metal content and dispersion rate.Figure shows the hydrogen storage behaviors of the Pt/PGNF samples. It was found that all of the Pt/PGNF samples showed higher hydrogen uptake than did the PGNF sample (0.25 mass%).
Keywords: Hydrogen storage; Porous graphite nanofibers; Pt nanoparticles
Bounds for local and average microwave absorption in heterogeneous systems
by R. Pelster (pp. 534-540).
A simple expression for the local energy loss rate in binary mixtures is derived that can be used to analyze measured dielectric spectra, to check their validity or to control whether the specified material composition is consistent. Together with well-known permittivity bounds it is applied to analyze recently published data on microwave absorption of emulsions containing aqueous micro- and nano-droplets. It follows that these data are inconsistent and violate energy conservation.A simple expression for the local energy loss rate in binary mixtures is derived. Together with well-known permittivity bounds it is applied to analyze recently published data of emulsions containing aqueous micro- and nano-droplets.
Keywords: Microwave heating; Interface polarization; Effective medium theory; Emulsions