Journal of Colloid And Interface Science (v.331, #2)
Functionalized gold nanoparticles: Synthesis, structure and colloid stability
by Jingfang Zhou; John Ralston; Rossen Sedev; David A. Beattie (pp. 251-262).
Gold nanoparticles and their arrays are some of the most studied nanomaterials, with promising applications in many fields such as electronics, optoelectronics, catalysis and biology. In order to protect bare gold nanoparticles from aggregation, to manipulate the optical, electronic and catalytic properties of the gold core, as well as to control interfacial properties, the gold nanoparticles are generally capped by an organic layer. Previous studies [C.D. Bain, G.M. Whitesides, J. Am. Chem. Soc. 110 (1988) 3665–3666] have revealed that many phenomena (e.g., wetting, friction and adhesion), are sensitive to the top few angstroms of a surface. The interfacial properties of a gold surface derivatized with a self-assembled monolayer will thus be dictated by the functionalities present on the outer side of the monolayer. The synthesis, functionalization and surface structure of monolayer-protected gold nanoparticles have been intensively studied in recent times [M.-C. Daniel, D. Astruc, Chem. Rev. 104 (2004) 293–346]. In addition, the aggregation and dispersion of colloidal nanoparticles is one of the key issues related to their potential applications. The forces that govern the colloid stability of nanoparticle dispersions, and how to control them, have yet to be fully investigated. Here special attention has been paid to control of colloid stability using external stimuli. In this feature article, the following five areas are reviewed: synthesis and applications of nanostructured particles; formation and structure of self-assembled monolayer protected gold nanoparticles; colloid stability—DLVO and non-DLVO forces; photochemistry, photochromism and pyrimidine; and manipulation of colloid stability with external stimuli.
Keywords: Gold nanoparticles; Functionalization; External stimuli; Nanostructure; Colloid stability
Electrolyte ion effects on Cd2+ binding at Al2O3 surface: Specific synergism versus bulk effects
by Chariklia Kosma; Georgia Balomenou; George Salahas; Yiannis Deligiannakis (pp. 263-274).
Cd2+ binding on γ-Al2O3 was studied in the presence of the common electrolyte ions Mg2+, SO2−4, and NO−3 at high and low concentrations. Direct measurements were performed for Cd2+ as well as for electrolyte ion adsorption as a function of pH. The experimental data reveal that Cd2+ binding on γ-Al2O3 is modulated by the electrolyte ions in a complex manner. At high electrolyte concentration, Cd2+ uptake by γ-Al2O3 is inhibited. Theoretical analysis by a surface complexation model shows that this effect can be attributed partially to bulk, ionic strength, and effect of the electrolyte, but the most significant inhibition is due to direct competition between Mg2+ and Cd2+ ions for theSO− surface sites of γ-Al2O3. At low concentration of electrolyte ions, Cd2+ uptake by γ-Al2O3 can be enhanced due to synergistic co-adsorption of Cd2+ and electrolyte anions, particularly SO2−4 and to a lesser extent NO−3. The theoretical analysis shows that this co-adsorption is due to formation of ternary surface species (SOH2SO4Cd) and (SOH2NO3Cd) which enhance Cd-uptake at pH values well below the point of zero charge of the γ-Al2O3.
Keywords: Electrolyte; Cd; 2+; Ternary species; Synergistic; Ionic strength; FITEQL; γ; -Al; 2; O; 3
Effects of calcium ions on surface characteristics and adsorptive properties of hydrous manganese dioxide
by Ruiping Liu; Huijuan Liu; Zhimin Qiang; Jiuhui Qu; Guibai Li; Dongsheng Wang (pp. 275-280).
The effects of calcium ions (Ca2+) on the surface characteristics and adsorptive properties of hydrous manganese dioxide ( δMnO2), taking arsenic and humic acid as model pollutants, were systematically investigated. The FTIR spectra and SEM/EDX analyses indicate coordination between Ca2+ and the surface hydroxyls (Mn–OH) of δMnO2, which leads to an increase of the surface ζ potential. Ca2+ can facilitate δMnO2 aggregation, as indicated by the particle size distribution (PSD) and on-line flocculating index (FI). The variation of δMnO2 surface characteristics that is induced by Ca2+ enhances the adsorption of humic acid (HA) and arsenic onto δMnO2. The adsorption of HA is enhanced more significantly by Ca2+ than that of arsenic, which is positively related to the coordination strength between Ca2+ and individual pollutants. The SEM/EDX analysis shows the formation of Ca–HA complexes, which have a higher affinity for δMnO2 than HA. The bridging effect of Ca2+ plays a major role in enhancing HA adsorption onto δMnO2. Due to different interactions between Ca2+ and pollutants, the adsorption mechanism is pollutant-dependent in the presence of Ca2+.Ca2+ impacted the stability and the dynamic aggregation of δMnO2. Ca2+ at different concentrations changed the particle size distribution and significantly increased the particle diameter of δMnO2.
Keywords: Calcium ions; Surface characteristics; Adsorption; δ; MnO; 2; Humic acid; Arsenic
Contribution of1H NMR to the investigation of the adsorption of cationic Gemini surfactants with oligooxyethylene spacer group onto silica
by Anissa Bendjeriou-Sedjerari; Gaelle Derrien; Clarence Charnay; Jerzy Zajac; Louis Charles De Menorval; Marc Lindheimer (pp. 281-287).
The present study aims to investigate the behavior of a series of cationic Gemini surfactants with a hydrophilic spacer at liquid–gas and solid–liquid interfaces, with particular emphasis on the effect of spacer length. Gemini surfactants containing two quaternary ammonium groups bound by an ethylene oxide spacer chain, referred to as 12-EO x-12 withx=1,3,7 and 12 were synthesized. Surface tension measurements were used to show that the hydrophilic spacer with oxyethylene moieties was not fully extended at the air–water interface. With increasing the spacer group size, it became sufficiently flexible to adopt a particular conformation with a loop at the water side of the interface. A combined study by adsorption isotherm measurements and1H NMR spectroscopy allowed a detailed description of the adsorption mechanism of these investigated 12-EO x-12 surfactants, with NMR providing more precise information on the conformation of hydrophilic spacer at the solid–liquid interface. Binding to the silica surface involved one cationic headgroup for the surfactants with a short spacer and the two headgroups for the ones with a long spacer. The number of charged surface sites was estimated by considering the dimeric surfactant as a “molecular ruler.” The small density of adsorption sites gave rise to the formation of pinned surface micelles.Investigation of the interfacial properties of 12-EO x-12 gemini surfactants: spacer length effect on the molecule conformation at the liquid–gas and solid–liquid interfaces.
Keywords: Gemini surfactant; Micellization; Interfacial aggregation; Surface tension; 1; H NMR spectroscopy
Synergistic adsorption of mixtures of cationic gemini and nonionic sugar-based surfactant on silica
by Qiong Zhou; P. Somasundaran (pp. 288-294).
Adsorption behavior of cationicC12-C4-C12 gemini surfactant on silica has been investigated, along with that of nonionic surfactant n-dodecyl- β-d-maltoside (DM). While DM alone shows meager adsorption on silica, because of the lack of any electrostatic adsorption, cationic gemini adsorbs significantly on the oppositely charged silica surface. Due to the electrostatic nature of cationic gemini adsorption on silica, solution pH affects adsorption ofC12-C4-C12 gemini dramatically. Meanwhile,C12-C4-C12 gemini hemimicelle size at silica/water interface does not seem to change with solution pH. For the mixtures of DM and cationicC12-C4-C12 gemini, there is a sharp increase of DM adsorption at silica/water interface, up to 100 times more than DM alone. After mixing with DM, saturation adsorption of cationicC12-C4-C12 gemini decreases, due to competition for adsorption sites from DM. At the same time, in its mixture with DM, there is an increased adsorption ofC12-C4-C12 gemini in the rising part of the adsorption isotherm. Hydrophobic chain–chain interactions, especially with two hydrophobic chains in oneC12-C4-C12 gemini molecule, and adsorbedC12-C4-C12 gemini molecule acting as an anchor or nucleation sites for forming mixed aggregates with DM on silica surface, are attributed to the marked adsorption synergy between DM and cationicC12-C4-C12 gemini. The adsorption of surfactants and their mixtures has a marked effect on silica surface charge and silica's wettability.Enhanced nonionic n-dodecyl- β-d-maltoside (DM) adsorption by synergistic adsorption with cationic gemini surfactant from their mixtures on silica surfaces.
Keywords: Cationic gemini; Sugar-based surfactant; Interfaces; Hemimicelle; Adsorption; Surfactant interaction
Sorption phenomena of modification of clinoptilolite tuffs by surfactant cations
by M. Rožić; Đ. Ivanec Šipušić; L. Sekovanić; S. Miljanić; L. Ćurković; J. Hrenović (pp. 295-301).
The sorption of cationic surfactant hexadecyltrimethylammonium (HDTMA) onto the solid/liquid interfaces of different clinoptilolite rich tuffs (CT) is examined. Examined were CT from Serbia with 75% clinoptilolite, CT from Turkey with 70% clinoptilolite, and CT from Croatia with 60% clinoptilolite. The sorption of HDTMA cations increased in the following order: CT from Serbia>CT from Turkey>CT from Croatia. The maximum amounts of sorbed HDTMA cations, normalized with regard to external cation exchange capacities of tuffs, were 1.79, 1.70, and 1.14 for Serbian, Turkish, and Croatian CT. FTIR analysis of samples with the maximum amount of sorbed HDTMA cations showed that HDTMA chains on Serbian CT adopt mainly a stretched all- trans conformation, while at the surfaces of CT from Turkey and Croatia the amount of gauche conformations increased. The zeta potentials of CT samples with the maximum amount of sorbed HDTMA cations and the sorption of benzoate anions on these samples increased in the following order: CT from Turkey>CT from Serbia>CT from Croatia. It can be assumed that on the surface of CT from Turkey iron (hydr)oxide clusters or nanoparticles with positive surface sites are present, due to which the isoelectric point is sifted toward lower and the zeta potential toward higher values. Therefore, the sorption of benzoate anions on modified CT from Turkey is also higher.FTIR spectra of HDTMA (a) and HDTMA sorbed onto clinoptilolite tuffs from Serbia (with approximately 75% clinoptilolite) (b), Turkey (with approximately 70% clinoptilolite) (c), and Croatia (with approximately 60% clinoptilolite) (d). HDTMA chains on Serbian CT adopt mainly stretched all- trans conformation, while at the surfaces of CT from Turkey and Croatia the number of gauche conformations increases.
Keywords: Benzoate anions; Clinoptilolite tuff; Hexadecyltrimethylammonium bromide; Sorption; Zeolite
A thermodynamic analysis of gas adsorption on microporous materials: Evaluation of energy heterogeneity
by Joan Llorens; Marc Pera-Titus (pp. 302-311).
This paper presents a thermodynamic isotherm derived from solution thermodynamics principles to describe gas adsorption on microporous materials. This isotherm relies on a potential relationship between the integral free energy of adsorption relative to saturation,Ψ/RT, expressed by the Kiselev equation, and the variableZ=1/−Ln(Π), being Π the relative pressure. A mathematical analysis reveals that the adsorption energy heterogeneity in the micropores is collected in a characteristic parameter of the isotherm, m, that can be related to the α parameter of the Dubinin–Astakhov isotherm in a simple way(m=α+1). The isotherm also predicts a plateau inΨ/RT at extremely low pressures (Π<10−7). Neimark's thermodynamic equation accounting for gas adsorption on mesoporous solids is found to be a particular case of the isotherm presented in this study. The Langmuir isotherm only shows consistency with the thermodynamic isotherm for a reduced combination of values of the relevant parameters, not usually found in common adsorbents. The suitability of the thermodynamic isotherm is experimentally assessed by testing a collection of microporous materials, including activated carbons, carbon nanotubes, and zeolites.
Keywords: Microporous material; Gas adsorption; Energy heterogeneity; Fractal; Dubinin–Astakhov; Langmuir
Hysteresis in the individual and competitive sorption of cadmium, copper, and lead by various soil horizons
by F.A. Vega; E.F. Covelo; M.L. Andrade (pp. 312-317).
Investigations of the sorption of heavy metals by soils often involve a fast ion-exchange process followed by a more sorbate-specific slow process. Desorption and sorption isotherms often fail to coincide, thus showing real or artifactual hysteresis, and failure to conform to conventional models generally prevents meaningful comparison of the hysteretic behavior of different sorbates in different soils. In the work described here, the irreversibility of the sorption of Cd, Cu, and Pb from single-metal and multimetal solutions by samples of 20 soil horizons was evaluated in terms of a hysteresis index, defined as the ratio between the values obtained in desorption and sorption experiments for an affinity measure defined in previous work,Kr. Sorption of these metals from both types of solution was more irreversible in the more basic soils, and its other chief determinants were CICe, Mn oxides content, and, except for Cd, organic matter content. The least sorbed metal was invariably Cd.Hysteresis in the individual and competitive sorption of cadmium by twenty soil horizons.
Keywords: Soil; Sorption; Hysteresis; Cd; Cu; Pb; Single- and multimetal solutions
Electrostatic deposition of polycations and polyanions onto cysteine monolayers
by Wesley Sanders; Mark R. Anderson (pp. 318-321).
Electrochemical impedance spectroscopy and the quartz crystal microbalance are used to monitor the deposition of polyelectrolytes onto an interface modified with a monolayer of cysteine. When using an anionic redox probe, Fe(CN)−46, the impedance of the cysteine modified electrode is a function of the solution pH; the charge-transfer resistance being higher at basic pH, and smaller under acidic conditions relative to the value found when the solution is buffered near the pI for cysteine. This behavior is consistent with the electrostatic interaction between the anionic redox probe and the net charge of the interface. After exposure of the cysteine-modified interface to 0.10 mol L−1 HCl solutions containing polystyrene sulfonate, the impedance of the modified interface increases. This behavior is consistent with the interface having a net negative charge, and suggests that the polyanion is confined to the interface. Quartz crystal microbalance measurements also show that700±20ng of the PSS is deposited under the acidic conditions. After exposure to 0.10 mol L−1 NaOH solutions containing poly(diallyldimethyl)ammonium chloride, the impedance of the modified interface decreases, consistent with the electrostatic assembly of the polycation to the cysteine monolayer under these conditions. Quartz crystal microbalance measurements indicate that770±40ng of the poly(diallyldimethylammonium chloride) are deposited under the basic conditions.The net charge of a cysteine monolayer is controlled by altering the solution pH. This is diagnosed experimentally by impedance spectroscopy, and allows control of the interfacial charge density for subsequent electrostatic assembly of either polycations or polyanions.
Keywords: Electrostatic self-assembly; Electrochemical impedance spectroscopy; Cysteine; Polyelectrolyte
Assessing the feasibility of hydrate deposition on pipeline walls—Adhesion force measurements of clathrate hydrate particles on carbon steel
by Joseph W. Nicholas; Laura E. Dieker; E. Dendy Sloan; Carolyn A. Koh (pp. 322-328).
Adhesive forces between cyclopentane (CyC5) hydrates and carbon steel (CS) were measured. These forces were found to be substantially lower than CyC5 hydrate–CyC5 hydrate particle measurements and were also lower than ice–CS measurements. The measured adhesive forces were used in a force balance to predict particle removal from the pipeline wall, assuming no free water was present. The force balance predicted entrained hydrate particles of 3 microns and larger diameter would be removed at typical operating flow rates in offshore oil and gas pipelines. These predictions also suggest that hydrate deposition will not occur in stabilized (cold) flow practices.Adhesion force measurements of a hydrate particle and steel surface (a–d).
Keywords: Hydrate deposition; Cyclopentane hydrate; Steel; Adhesive force; Hydrate removal
Design of liquid/solid adsorption isotherms by energy distribution functions
by Grit Kalies; Peter Bräuer; Michael v. Szombathely (pp. 329-334).
Synthetic energy distributions and corresponding adsorption isotherms of binary liquid mixtures are presented. The relevance of information on a solid's energetic heterogeneity from liquid-phase adsorption isotherms is studied.Adsorption excess isotherms of binary liquid mixtures have been calculated from synthetic adsorption energy distribution functions characterizing energetic heterogeneity at the liquid/solid interface. In order to see consequences for the adsorption isotherms, the distribution functions were varied systematically. In this way, the sensitivity or the lack of sensitivity of liquid-phase adsorption isotherms over the whole concentration range for changes in energy distribution functions became evident. The question of to what extent it makes sense to use liquid adsorption measurements to obtain relevant information on a solid's energetic heterogeneity is answered.
Keywords: Adsorption excess isotherm; Binary liquid mixture; Adsorption energy distribution function; Adsorption integral equation
Gelling nature of aluminum soaps in oils
by Xr. Xiaorong Wang; Mindaugas Rackaitis (pp. 335-342).
Aluminum soaps are notable for their ability to form soap-hydrocarbon gels of high viscosity. For more than half a century, it has been believed that the gelling mechanism is due to a formation of polymeric chains of aluminum molecules with the aluminum atoms linking along the axis and with the fatty acid chain extended sideways. Here we report results from an investigation using high-resolution electron microscopy and rheology measurements that clearly resolve the ambiguity. Our results reveal that the gelling mechanism stems from the formation of spherical nano-sized micelles from aluminum soap molecules, and those colloidal micelle particles then aggregate into networks of highly fractal and jammed structures. The earlier proposed polymer chain-like structure is definitely incorrect. The discovery of aluminum soap particles could expand application of these materials to new technologies.This work demonstrates that aluminum soaps form spherical micelles in oils and that the aggregation of these micelles forms a network that gives rise to the gel formation—thereby refuting a long-held belief that the gel formation was the result of linear polymeric chains of aluminum association.
Keywords: Aluminum soap; Soap-hydrocarbon gels; Rheology; Electron microscopy; Fractal network; Colloidal micelle particle; Jamming
Temperature-responsive polymer brush constructed on a colloidal gold monolayer
by Hiromi Kitano; Hirokazu Kago; Kazuhiro Matsuura (pp. 343-350).
Polymers of 2-(2-methoxyethoxy)ethyl methacrylate (MDM) were prepared by atom transfer radical polymerization using 2-(2′-bromoisobutyroyloxy)ethyl disulfide as initiator. An aqueous solution of the disulfide-carrying polymer (DT-PMDM) turned to be opaque above certain temperature (22 °C for DT-PMDM (Mn=1.69×104)), which was corresponding to the lower critical solution temperature (LCST) of the polymer. The disulfide-carrying polymer could be accumulated on the surface of gold colloid as a polymer brush as confirmed by the increase in absorbance at 550 nm ascribable to the localized surface plasmon resonance (LSPR). Furthermore, the polymer brush could also be constructed on a monolayer of colloidal gold that had been deposited on a glass plate beforehand. The PMDM brush on both the free and surface-confined gold colloids showed definite temperature responsiveness in the absorbance at 550 nm. Moreover, non-specific adsorption of various proteins to the surface of polymer brush on the glass plate was examined by the absorption increase at 550 nm. The PMDM brush, which had been prepared with the DT-PMDM pretreated with NaBH4, did not adsorb lysozyme significantly below the LCST of the polymer chain, whereas substantially adsorbed the protein above the LCST. These results suggest usability of the polymer brushes with pendent ω-methoxy oligo(ethylene glycol) groups to coat various materials for biomedical applications.Temperature-responsive polymer brush constructed on a colloidal gold monolayer.
Keywords: Atom transfer radical polymerization; Localized surface plasmon resonance; Lower critical solution temperature; Polymer brush; Protein adsorption; Temperature-responsiveness
Encapsulation of submicrometer-sized silica particles by a thin shell of poly(methyl methacrylate)
by I. Freris; D. Cristofori; P. Riello; A. Benedetti (pp. 351-355).
Polymer encapsulation of submicrometer-sized silica particles by synthesis of the polymer shell, poly(methyl methacrylate) under static conditions in a reaction medium free of surfactants and stabilizing agents is described. The Stöber method, a base-catalyzed hydrolysis and condensation of tetraethyl orthosilicate is used for the synthesis of the monodisperse colloidal dispersion of silica particles. The silica particles are subsequently modified in situ with the surface grafting of the silane coupling agent, 3-(trimethoxysilyl)propyl methacrylate. Encapsulation is achieved using tetraethyl orthosilicate as a reaction medium, in which a thermally initiated radical polymerization of methyl methacrylate is promoted in the presence of the modified particles by a seeding method which leads to a thin coating of poly(methyl methacrylate), and hence silica core–shell particles. The complete encapsulation of individual silica spheres by poly(methyl methacrylate) is visually evidenced by TEM microscopy which reveals the presence of a polymer shell coating up to 10 nm. Evidence for the presence of a poly(methyl methacrylate) shell is further corroborated by DSC/TGA, DRIFT-IR and NMR measurements.Thin shell coatings of poly(methyl methacrylate) were formed on the surface of functionalized silica particles by polymerization of methyl methacrylate in a medium of tetraethyl orthosilicate under static conditions.
Keywords: Encapsulation; Silica; Poly(methyl methacrylate); Polymerization; Coupling agent; Surface functionalization; Organic–inorganic hybrid
Characterization and micellization of rhamnolipidic fractions and crude extracts produced by Pseudomonas aeruginosa mutant MIG-N146
by Yan-Ping Guo; Yong-You Hu; Roy R. Gu; Hui Lin (pp. 356-363).
Two representative rhamnolipidic fractions, RL-F1 and RL-F2, produced by the P. aeruginosa mutant strain MIG-N146, were separated and chemically characterized by TLC, HPLC-MS, and FTIR. The RL-F1 fraction is predominantly mono-rhamnolipid homologues with a high content of one or two fatty acid moieties. The RL-F2 fraction is mainly composed of di-rhamnosyl moieties with two hydrophobic tails. Micellization behavior was investigated to assess the physicochemical properties of the surfactants, RL-F1, RL-F2, and crude rhamnolipidic extracts. The variations in morphology of micelle formation and growth were examined by dynamic light scattering measurements as a function of surfactant concentration. Critical micelle concentration (CMC), average minimal surface tension (γCMC), saturated surface excess (Γm), mean surface area per molecule ( S), and adsorption efficiency ( pC20) were determined from the surface tension profiles and compared for the three surfactant systems. It was found that micelle growth was significantly enhanced by increasing rhamnolipid bulk concentration, which was most probably accompanied with an aggregate shape transition. Well-separated multi- or bi-modal distributions of particle size were observed in RL-F2 and the crude extracts solutions. The results of this study demonstrate that molecular architecture of different surfactant compositions profoundly influences the performance of rhamnolipidic surfactants.Changes in particle size for rhamnolipidic fractions and crude extracts as a function of concentration.
Keywords: Rhamnolipids; HPLC-MS; Homologues; Surface property; Micellization behavior
Modeling the dynamic folding and surface-activity of a helical peptide adsorbing to a pendant bubble interface
by Vikas P. Jain; Charles Maldarelli; Raymond S. Tu (pp. 364-370).
We have designed a peptide with switchable surface activity, where the folded ( α-helical) form of the peptide is amphiphilic and the unfolded form is not. To understand the factors influencing the dynamics of the switchability, a model is developed for the transport of the surface active form of the peptide from the solution onto air–water interface. As is the case with the low molecular weight head–tail surfactants, the transport involves the bulk diffusion of the folded form to the surface and the kinetic adsorption onto the interface. Unlike the head–tail surfactants, the diffusion can be augmented by the kinetics of the folding of the peptide from the unfolded form. The model is formulated within the context of the transport of the peptide from a uniform bulk solution onto an initially clean air–water interface in a pendant bubble system, where the transport rate can be measured by recording the reduction in surface tension using the shape analysis of the bubble. Experiments are undertaken and compared to the predictions of the model simulations of the tension reduction for a range of values of the kinetic adsorption constant and the folding kinetic constant. The results indicate that the kinetic adsorption rate of the folded peptide onto air–water interface dominates the dynamic process, which contrasts many head–tail surfactants where diffusion typically dominates over kinetics adsorption. Moreover, our ‘best-fits’ suggest that there is a phase transition at high surface concentrations that slows the long-time adsorption of the peptides to the interface. Finally, the numerical solution is compared with an asymptotic solution, showing agreement with our findings that the fundamental dynamics of the tunable surface-active peptide are indeed controlled by the adsorption step.We develop a transport model to characterize the sublayer concentrations of a tunable amphiphilic peptide at the air–water interface of a pendant bubble.
Keywords: Peptide; Tunable surface activity; Helical; Pendant bubble; Folding and unfolding; Ward and Tordai; Asymptotic
Adhesion between highly rough alumina surfaces: An atomic force microscope study
by Marie-Charlotte Audry; Stella Ramos; Elisabeth Charlaix (pp. 371-378).
The removal of contaminant particles in microelectronics processes now extends not only to the compounds themselves but also to the reactor pieces where they are fabricated. This raises new issues as both the particles and the reactor walls are highly rough and a maximum number of particles per unit area is tolerated. In this work we study the adhesion force of a sapphire particle onto alumina substrates of roughness ranging from 10 nm to 3 μm peak-to-peak on a5μm×5μm area, in water. A contribution of this work is the prediction of the statistic of the adhesion force by a fast running numerical computation, without any adjustable parameters. The perspective is to be able to predict the best conditions for removing contaminant particles.
Keywords: Particle adhesion; Surface roughness; Ultra-cleaning
Study on modification of colloidal silica surface with magnesium ions
by Asghar Karami (pp. 379-383).
The prepared colloidal silica via ion exchange was modified by adding Mg+2 ions in the surface growth process of colloidal silica. The particle size of the modified colloidal silica was decreased by increasing the seed concentration, whereas that of colloidal silica was slightly increased as the seeds concentration exceed 15 wt%. But the trend of changes in surface area was completely reversed. Magnesium ions on surface of the modified colloidal silica were identified by the measurement of energy-dispersive X-ray spectrometry (EDS). After modifying with Mg+2 ions, the iso-electric point (IEP) of colloidal silica inpH∼2 without modification, disappears over the whole pH range.Modification of the colloidal silica in different conditions, low and high concentrations of seed and Mg+2, resulted in compounds with the different particle size distribution, stability and various morphologies.
Keywords: Magnesium ions; Colloidal silica; Sodium silicate; Surface area
Efficient preparation of silver nanoplates assisted by non-polar solvents
by Lijian Huang; Yueming Zhai; Shaojun Dong; Jin Wang (pp. 384-388).
In the paper, we report an efficient method to prepare high yield (up to 97%) of silver nanoplates. Synthesis of silver nanoplates was carried out in a binary solvent system ofN,N-dimethylformamide (DMF) and toluene, in which DMF served as the reductant and polyvinylpyrrolidone (PVP) as the capping agent. By increasing the ratio of toluene to DMF to 7:6, silver nanoplates can be successfully synthesized; otherwise other shaped nanoparticles would be the major products. The nanoplate sample was characterized by TEM, HRTEM, SAED, XRD, AFM and UV–visible spectroscopy, proving the high nanoplate purity of this sample. The influence of toluene content, other solvents, AgNO3 concentration, preparation temperature and chloride ions was also examined, which suggests that the function of non-polar solvents in this system is to enhance the PVP coverage on silver surface and, furthermore, to facilitate the preferential adsorption of PVP on two (111) facets of silver nanoplates.TEM image and XRD pattern of a Ag nanoplate sample prepared by adding toluene as the co-solvent.
Keywords: Silver nanoplates; Non-polar solvents; Toluene; DMF; Polyvinylpyrrolidone
A facile method for the fabrication of vinyl functionalized hollow silica spheres
by Hongting Pu; Xiong Zhang; Junjie Yuan; Zhenglong Yang (pp. 389-393).
In this paper, we adopt a facile method to prepare vinyl functionalized hollow silica spheres. Vinyl functionalized silica shells were coated on positively charged polystyrene particles by hydrolysis and condensation of vinyltriethoxysilane (VTES), the polystyrene cores were dissolved subsequently in the same medium to form monodispersed vinyl functionalized hollow silica spheres. Neither additional dissolving nor a calcination process is necessary to remove the polystyrene cores. Transmission electron microscopy (TEM), FT-IR analysis, TGA and porosity measurements were used to characterize the monodispersed vinyl functionalized hollow silica spheres.Vinyl functionalized hollow silica spheres were synthesized through hydrolysis and condensation of vinyltriethoxysilane on positively charged polystyrene templates. The shell of the obtained hollow spheres possessed 12.7 mmol/g vinyl groups theoretically. Figure: TEM image of vinyl functionalized hollow silica spheres.
Keywords: Vinyl functionalized hollow silica sphere; Porous
Optical and electron microscopy studies of Schiller layer formation and structure
by Dorothy Farrell; Cindi L. Dennis; JitKang Lim; Sara A. Majetich (pp. 394-400).
Iridescent Schiller layers were prepared by centrifugation of β-FeOOH sols with an initial particle concentration of 1014 particles/mL, reducing the Schiller layer formation time from over 2 months to 3 weeks. The formation and structure of the Schiller layers were investigated using optical and transmission electron microscopy. Microscopy studies revealed the self-assembly to proceed by the formation of two-dimensional particle arrays followed by the stacking of these arrays to form the final iridescent state. Varying the pH showed that Schiller layer formation occurs only in the pH range 1.4–2.0, indicating that electrostatic interactions play a pivotal role in the self-assembly. Decreasing the particle concentration of the sols was found to inhibit the assembly. DLVO theory and order–disorder phase transition models were found to be insufficient to accurately model the experimental behavior. Several approaches were investigated in an attempt to make ferrimagnetic arrays from the Schiller layers. The most promising was via electron beam irradiation, which transforms the β-FeOOH into γ-Fe2O3 without altering the shape of the nanorods.TEM micrograph showing self-assembled array of nanorods.
Keywords: Schiller layers; Colloids; Self-assembly; β; -FeOOH; Nanorods
Effect of anchoring group on the photosensitization of colloidal TiO2 nanoparticles with porphyrins
by A. Kathiravan; R. Renganathan (pp. 401-407).
The interaction of porphyrins (TCPP, TSPP, TMeOPP and TPP) with colloidal TiO2 nanoparticles was studied by infra-red, UV–visible absorption, steady state and time resolved fluorescence spectroscopy. The porphyrins (TCPP, TSPP and TMeOPP) adsorbed on the surface of colloidal TiO2 nanoparticles through electrostatic interaction. According to absorption and fluorescence changes the apparent association constants (Kapp) were calculated. However, TPP did not interact with surface of colloidal TiO2 nanoparticles due to the absence of anchoring group. The fluorescence quenching is attributable mainly to electron transfer from the excited state porphyrins to the conduction band of colloidal TiO2. The rate of electron transfer process (ket) was calculated using lifetime measurement. The electron transfer mechanism has been proved by the calculation of free energy change (ΔGet) by applying Rehm–Weller equation. Using all the spectroscopic measurements we confirmed that the presence of anchoring group plays major role in the adsorption as well as the electron transfer processes.The molecular interaction of porphyrin adsorbed on the surface of colloidal TiO2. TCPP adsorbed on the surface of TiO2 through its anchoring group, but TPP shows no interaction with TiO2, due to the absence of anchoring group.
Keywords: Porphyrins; Fluorescence quenching; Colloidal TiO; 2
Understanding molecular structures of silanes at buried polymer interfaces using sum frequency generation vibrational spectroscopy and relating interfacial structures to polymer adhesion
by Anne V. Vázquez; Nick E. Shephard; Cheryl L. Steinecker; Dongchan Ahn; Sarah Spanninga; Zhan Chen (pp. 408-416).
The use of silane adhesion promoters to improve adhesion of elastomeric materials to polymers has become increasingly common in many industrial applications. However, little is understood about the molecular-level mechanisms of how adhesion promoters enhance adhesion. Here, sum frequency generation (SFG) vibrational spectroscopy was used to probe the buried interface between poly(ethylene terephthalate) (PET) and (3-glycidoxypropyl)trimethoxysilane ( γ-GPS), and the interface between PET and a mixture of γ-GPS and a methylvinylsiloxanol (MVS), a known adhesion-promoting mixture. Furthermore, the interfaces between PET and uncured silicone with incorporated silane or silane mixture and the interfaces between PET and cured silicone with incorporated silane or silane mixture were studied. The γ-GPS methoxy groups were found to order at the polymer interface and the presence of MVS increased the interfacial segregation and/or order of γ-GPS. For comparison, two other silanes, N-octadecyltrimethoxysilane (OTMS) and (tridecafluoro-1,1,2,2-tetrahydroctyl)trimethoxysilane (TDFTMS), as well as their mixtures with MVS were also studied at the various interfaces, and were found to exhibit different interfacial behaviors than γ-GPS and the known silane adhesion-promoting mixture of γ-GPS and MVS. Further, X-ray photoelectron spectroscopy (XPS) was used to investigate the exposed PET surfaces resulting from peeling the PET/cured silicone elastomer with TDFTMS and with the TDFTMS/MVS mixture interfaces, and it was shown that the fluorinated silane does segregate to the polymer interface. When correlated to adhesion testing results, it is inferred that segregation and ordering of the silane methoxy groups at the polymer/silane and polymer/silicone elastomer interfaces is crucial for adhesion promotion in this system.SFG spectra have been successfully collected from the buried PET/cured PDMS (with silane or silane mixture) interface. Only γ-GPS molecules are ordered at this buried interface. No SFG signal was detected from two other types of silane molecules.
Keywords: Sum frequency generation; Silane coupling agents; Interfacial structure; Polymer adhesion; PDMS; PET
Preparation of a microporous layered organic–inorganic hybrid nanocomposite using p-aminotrimethoxysilane and a crystalline layered silicate, ilerite
by Ryo Ishii; Takuji Ikeda; Fujio Mizukami (pp. 417-424).
The silylation of ilerite with p-aminophenyltrimethoxysilane (denoted as APhS) was conducted in order to attempt preparation of a layered organic–inorganic hybrid nanocomposite having interlayer microporosity, in which the APhS molecule bridges between the silicate layers using two heterofunctional groups containing an amino group and a methoxy one. The APhS molecules were successfully condensed and immobilized in the interlayer of the protonated ilerite. Chemical analysis and29Si solid-state NMR results indicated that the interlayer space was occupied by preferential condensation between the APhS molecules. Subsequent HCl treatment could remove the excess amounts of the oligomeric species of the APhS molecules. The removal brought about vacant spaces in the interlayer supported by the bridging of the residual APhS molecules. Furthermore, the immobilized APhS molecules had a significant influence on the surface properties of the resultant nanocomposite, which showed high toluene adsorptivity. Consequently, we found a means to construct a microporous, layered nanocomposite by the bridging of the organic spaces with two heterofunctional groups.The silylation of ilerite with p-aminophenyltrimethoxysilane has successfully yielded interlayer microporosity by bridging with phenylene units between the silicate layers, using two heterofunctional groups, an amino group and a methoxysilyl one.
Keywords: Nanocomposite; Microporosity; Intercalation; Silylation; Ilerite; Octosilicate; p; -Aminophenyltrimethoxysilane
EDTA modified LDHs as Cu2+ scavengers: Removal kinetics and sorbent stability
by Ricardo Rojas; M. Rosario Perez; Eustaquio M. Erro; Patricia I. Ortiz; Maria Angeles Ulibarri; Carla E. Giacomelli (pp. 425-431).
EDTA modified layered double hydroxides (LDHs) were investigated as potential sorbents to remediate heavy metals pollution. The polidentate ligand was introduced by an exchange method in a Zn–Al-LDH, which takes place with partial erosion of the layers, causing the intercalation of [Zn(EDTA)]2− complex instead of the ligand. [Cu(H2O)6]2+ cation was selected as a model cation to study the uptake mechanism, exploring the elimination kinetics from the first minutes up to the steady state. A flow injection analysis system coupled to an amperometric detector (FIA-AM) was applied to perform fast and reliable [Cu(H2O)6]2+ determinations in monodisperse solid–aqueous solution systems. Furthermore, the sorbent stability was determined as a function of the pH and the nitrate concentration. The [Cu(H2O)6]2+ elimination is produced by an exchange reaction with [Zn(EDTA)]2− anions placed either in the solid interlayer or in the aqueous solution, this last being released from the sorbent. Additional [Cu(H2O)6]2+ removal is produced by Cu(OH)2 precipitation at high copper concentrations due to the LDHs high pH buffering capacity. The sorbent removes [Cu(H2O)6]2+ with high affinity in a wide concentration range. The elimination process reaches equilibrium in less than 30 min and leaves metal cation concentrations lower than 0.05 ppm in the supernatants.Schematic representation of the LDH modification process (a) and the scavenging mechanisms (b).
Keywords: Layered double hydroxides; Kinetics; Uptake; Heavy metals remediation
Synthesis of ZSM-5 with intracrystal or intercrystal mesopores by polyvinyl butyral templating method
by Haibo Zhu; Zhicheng Liu; Dejin Kong; Yangdong Wang; Xiaohong Yuan; Zaiku Xie (pp. 432-438).
Three facile routes were utilized to synthesize ZSM-5 materials with intracrystal or intercrystal mesopores, where the polyvinyl butyral gel served as mesopore directing template. The three routes were divided into two synthesis strategies: the hydrothermal treatment of silica/PVB composite and re-crystallization of preformed zeolite precursor with the assistance of PVB gel. The fabrication of silica/PVB composite was accomplished by two routes including sol–gel process and impregnation method. The resulting composite was undergone hydrothermal treatment. During the crystallization PVB was occluded in the ZSM-5 crystal, creating intracrystal mesopores in the zeolite. The last route for the synthesis of mesoporous ZSM-5 was realized by re-crystallization of preformed ZSM-5 zeolite in the presence of PVB. This route involved the pre-crystallization of the amorphous aluminosilicate to produce the pre-formed ZSM-5 precursor. Upon further crystallization of the mixture of PVB gel and pre-formed ZSM-5, the ZSM-5 precursor was transformed into ZSM-5 aggregate of nanocrystals, while the PVB gel was occluded in the ZSM-5 particles. Removal of the template generated the typical microporosity associated with ZSM-5 structure along with intercrystal mesoporosity produced from the PVB. The mesoporous ZSM-5 exhibited enhanced catalytic activity in the toluene disproportionation and transalkylation with C9 and C10 aromatics.The ZSM-5 zeolites with intracrystal or intercrystal mesopores were synthesized by using the polyvinyl butyral gel as the mesopore directing template, and the mesoporous ZSM-5 exhibited improved catalytic activity.
Keywords: Zeolite; ZSM-5; Mesoporous zeolite; Polyvinyl butyral; Templating synthesis; Hydrothermal synthesis
Synthesis and characterization of arsenate-intercalated layered double hydroxides (LDHs): Prospects for arsenic mineralization
by S.V. Prasanna; P. Vishnu Kamath (pp. 439-445).
The arsenate-intercalated layered double hydroxide (LDH) of Mg and Al is synthesized by coprecipitation. The higher thermodynamic stability and the consequent lower solubility of the unitary arsenates preclude the formation of arsenate-intercalated LDHs of other metals directly from solution. However other M/Al-AsO4 (M=Co, Ni, Zn) LDHs could be prepared by anion exchange, showing that arsenate intercalation proceeds topotactically. The intercalation of various species of As(V) into the interlayer of LDHs and the subsequent arsenate carrying capacity are dependent upon the pH of the solution. Upon thermal decomposition, the intercalated arsenate ion undergoes reductive deintercalation to give a mixture of As(III) and As(V) oxides. The product oxides revert back to the LDH upon soaking in water on account of the compositional and morphological metastability of the former. This is in contrast with the phosphate-intercalated LDHs, in which the reversibility is suppressed, consequent to the formation of stable metal phosphates.pH plays a significant role in arsenate uptake by LDHs. Arsenic speciation results in the formation of compounds with different basal spacings.
Keywords: Arsenic; Layered double hydroxides; Reversible thermal behavior; Arsenate exchange
Fabrication of robust honeycomb polymer films: A facile photochemical cross-linking process
by Lei Li; Caikang Chen; Aijuan Zhang; Xinyu Liu; Kun Cui; Jin Huang; Zhi Ma; Zhaohui Han (pp. 446-452).
Highly ordered honeycomb films are prepared by breath-figure method using an amphiphilic diblock copolymer of polystyrene- block-polyacrylic acid (PS- b-PAA). By simply cross-linking PS matrix via deep ultraviolet (UV) irradiation, both the solvent and thermal stability of the porous films was significantly improved while retaining the three-dimensional (3D) structures. The film surface wettability was changed from hydrophobicity to hydrophilicity by the formed polar groups during the photochemical process. After 6 h UV cross-linking, the honeycomb structures could be preserved up to 320 °C, an increase of more than 200 K as compared to the non-cross-linked films.Cross-section SEM image of PS- b-PAA film after UV exposure and thermal treatment up to 320 °C.
Keywords: Porous film; Block copolymer
Impregnating titanium phosphate nanoparticles onto a porous cation exchanger for enhanced lead removal from waters
by Kun Jia; Bingcai Pan; Lu Lv; Qingrui Zhang; Xiaoshu Wang; Bingjun Pan; Weiming Zhang (pp. 453-457).
Titanium phosphate (TiP) exhibits preferable sorption toward lead ion in the presence of competing calcium ions at high levels, however, it is present as fine or ultrafine particles and cannot be directly employed in fixed-bed or any flow-through systems due to the excessive pressure drop and poor mechanical strength. In the present study a new hybrid sorbent TiP-001 was fabricated by impregnating titanium phosphate (TiP) nanoparticles onto a strongly acidic cation exchanger D-001 for enhanced lead removal from waters. D-001 was selected as a host material mainly because of the Donnan membrane effect resulting from the immobilized sulfonic acid groups bound on the exchanger matrix, which would enhance permeation of the target metal cation prior to effective sequestration. TiP-001 was characterized by transmission electron micrograph (TEM), X-ray diffraction (XRD), and pH-titration. Batch and column sorption onto TiP-001 was assayed to evaluate its performance as compared to the host exchanger D-001. Lead sorption onto TiP-001 is a pH-dependent process due to the ion-exchange nature, and its sorption kinetics follows the pseudo-second-order model well. Compared to D-001, TiP-001 displays highly selective lead sorption in the presence of competing calcium cations at concentration of several orders higher than the target metal. Fixed-bed sorption of a synthetic feeding solution indicates that lead retention by TiP-001 results in a conspicuous decrease of this toxic metal from 0.50 to below 0.010 mg/L (drinking water standard recommended by WHO). Moreover, its feasible regeneration by dilute HCl solution also favors TiP-001 to be a feasible sorbent for enhanced lead removal from water.A new hybrid sorbent TiP-001 was fabricated by impregnating titanium phosphate (TiP) nanoparticles onto a porous cation exchanger D-001 for enhanced lead removal from waters.
Keywords: Titanium phosphate; Hybrid sorbent; Cation exchanger; Lead removal; Nanocomposite
Instability analysis of torsional MEMS/NEMS actuators under capillary force
by Jian-Gang Guo; Li-Jun Zhou; Ya-Pu Zhao (pp. 458-462).
The static and dynamic instabilities of a torsional MEMS/NEMS actuator caused by capillary effects are studied, respectively. An instability number, η, is defined, and the critical gap distance,gcr, between the mainplate and the substrate is derived. According to the values of η and g, the instability criteria of the actuator are presented. The dimensionless motion equation of the MEMS/NEMS torsional actuator is derived when it makes nonlinear oscillation under capillary force. The qualitative analysis of the nonlinear equation is made, and the phase portraits are presented on the phase plane. In addition, the bifurcation phenomena in the system are also analyzed.The phase orbits connecting three equilibrium points on the phase plane, which include the periodic, heteroclinic and homoclinic orbits.
Keywords: Torsional NEMS actuator; Capillary force; Instability; Bifurcation
The lyotropic phase behaviour of ester quaternary surfactants
by Gemma C. Shearman; Stephane Ugazio; Laurent Soubiran; John Hubbard; Oscar Ces; John M. Seddon; Richard H. Templer (pp. 463-469).
The lyotropic phase behaviour of two analogues of dioctadecyl dimethylammonium chloride was investigated. Both the inclusion of ester groups and subsequent minor structural rearrangement of the interfacial region of the surfactant were found to increase the chain melting temperature, although the overall phase behaviour remained similar for both compounds. Both of the two analogues were found to underswell, due to the formation of multi-lamellar vesicles. We also found that the inclusion of these ester linkages substantially reduced the metastability of the ‘gel phase’ in which the surfactants usually reside, accelerating the rate of collapse to a coagel state. This occurred via a nucleation-growth mechanism, where the growth was found to be one-dimensional, i.e. needle-like.
Keywords: Double-chained ester quaternary ammonium surfactants; Phase behaviour; Kinetics; Counterion condensation
Comparative studies of interactions of hemoglobin with single-chain and with gemini surfactants
by Yongsheng Wang; Rong Guo; Juqun Xi (pp. 470-475).
The interactions of hemoglobin with glutamic acid-based gemini surfactants and with n-dodecylammonium α-glutamate (GDA) were studied. The interactions between the protein and the surfactants with different structures and the mechanism of these interactions were illuminated.The interactions of hemoglobin with glutamic acid-based gemini surfactants (L2G2C n) and with n-dodecylammonium α-glutamate (GDA) have been studied with isothermal titration microcalorimetry, fluorescence spectroscopy, UV–vis spectroscopy, and circular dichroism. The results indicate that GDA monomer can make the hemoglobin denatured, and that when the concentration of GDA is higher than cmc, heme monomer is released from the hydrophobic cavity of hemoglobin. On the other hand, L2G2C n surfactants can also interact with hemoglobin. Compared with GDA, L2G2C n have a much smaller binding ability with hemoglobin, and the circular dichroism spectra results show that the secondary structure of hemoglobin is possibly stabilized by a small amount of L2G2C n, which may generate hydrophobic linkages between the nonpolar residues of hemoglobin. However, with further addition of L2G2C n, the secondary structure of hemoglobin is unfolded, and the percentage of α helix in hemoglobin molecule is decreased. In addition, the L2G2C n surfactant with a longer spacer can reduce the denaturing degree of hemoglobin.
Keywords: Hemoglobin; n; -Dodecylammonium; α; -glutamate; Gemini; Isothermal titration microcalorimetry
Synthesis and thermotropic liquid crystalline properties of heterogemini surfactants containing a quaternary ammonium and a hydroxyl group
by Tianhua Zhou; Jianxi Zhao (pp. 476-483).
A homologous series of novel heterogemini surfactants, (N,N-dimethyl- N-[3-(alkyloxy)-2-hydroxypropyl]-alkylammonium bromide (referred to as C mOhpNC n; m,n=10, 8; 12, 8; 14, 8; 16, 8; 14, 10; 12, 12 and 10, 14) were synthesized. Their thermotropic phase behavior was investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), infrared spectroscopy (IR) and X-ray diffraction (XRD). All the compounds showed high thermal stability and formed enantiotropic thermotropic smectic A liquid crystals. The mesophase region was sensitive to the overall length (m+n) of the two hydrophobic tails and was widened with increasing (m+n). When fixing the overall length of the two hydrophobic tails (m+n=24), the liquid crystal region was affected little by the dissymmetry of the two hydrophobic chains. The combination of IR and XRD results suggested the cis-configuration of the alkyl chain and the alkoxy chain with respect to the extended N–CH2–CH(OH) skeleton in both crystal lattice and liquid crystal mesophase. The folding of the alkoxy chain at the carbon atom connecting the hydroxyl group led to the hydrogen bonding between the hydroxyl and the Br− counterion, which is beneficial to stabilizing the liquid crystal phase.The newly synthesized heterogemini surfactants (N,N-dimethyl- N-[3-(alkyloxy)-2-hydroxypropyl]-alkylammonium bromides (referred to as C mOhpNC n; m,n=10, 8; 12, 8; 14, 8; 16, 8; 14, 10; 12, 12 and 10, 14), formed stable thermotropic liquid crystal over a wide temperature region.
Keywords: Heterogemini surfactant; Synthesis; Thermotropic liquid crystal; Hydrogen bonding
Stomatosomes, blastula vesicles and bilayer disks: Morphological richness of structures formed in dilute aqueous mixtures of a cationic and an anionic surfactant
by Rie Kakehashi; Göran Karlsson; Mats Almgren (pp. 484-493).
Cryogenic transmission electron microscopy (cryoTEM) was used to study the structures formed in mixtures of sodium dodecylsulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) in dilute aqueous solutions with 0–300 mM NaBr. The DTAB mole fraction, X, was in the range 0.2–0.4, limited at 25 °C by precipitation of solid DTA–DS atX=0.38 without salt toX=0.25 at 300 mM NaBr. At a total surfactant concentration of 100 mM the samples separated into two liquid phases (the bottom phase birefringent) within a narrow (±0.01 mole fraction units) composition range. At the mid-point X varied from 0.32 without salt to 0.22 at 300 mM NaBr. Elemental analysis of C, S, O, and N in the separated phases of a sample with 100 mM NaBr andX=0.26 showed the top phase to contain almost only SDS at a low concentration, 14 mM, and the bottom phase 175 mM total surfactant, withX=0.27. Elemental analysis on samples without added salt gave erratic results, indicating problems in the physical separation of the phases. The cryoTEM survey of the separated phases revealed similar problems. Without salt both phases showed similar structures, whereas the top phase in the sample with added salt was void of structures larger than small micelles. The cryoTEM survey revealed a variety of structures being simultaneously present in most samples. A general trend with increasing X was an evolution from globular micelles, over disks, bands, branched bands transforming into sparse webs, perforated bilayer structures, and finally smooth bilayers. Increasing salt and total surfactant concentrations resulted in the emergence of structures with smaller mean curvature at lower X. Perforated bilayers were found in samples with 100 mM or less of added salt, and usually persisted to DTAB contents where precipitates appeared. The porous bilayers seemed to derive from sparse webs of band-like structures, and the hole size decreased with increasing X and salt concentration. Two types of recurrent structures were noticed: blastula aggregates, seemingly an intermediate structure transforming crumpled bilayers into vesicles of similar size (diameter 400–500 Å), observed over a broad range of conditions, and at 100 mM total surfactant concentration and 50 mM added salt or more a type of regular disks with a diameter of180±30Å.0.24⩽[DTAB]/([SDS]+[DTAB])⩽0.34: From disks to perforated vesicles.
Keywords: Catanionic surfactants; Perforated vesicle; Disks; Micelles; CryoTEM; Bilayer
Surface and volume properties of dodecylethyldimethylammonium bromide and benzyldimethyldodecylammonium bromide
by Joanna Harkot; Bronisław Jańczuk (pp. 494-499).
Surface tension measurements were carried out for aqueous solutions of two cationic surfactants: dodecylethyldimethylammonium bromide (C12(EDMAB)) and benzyldimethyldodecylammonium bromide (BDDAB). Isotherms and thermodynamic adsorption parameters were determined from the surface tension data. Firstly, the surface excess concentration in the adsorbed monolayer and the total concentration of the surfactants were determined, then the standard free energy of adsorption was calculated by different methods. In the calculations, different orientations of the surfactants at the adsorbed monolayer were also taken into account. From the experimental and calculated data it results that the difference in the structure of the two cationic surfactants by changing the methyl group for aryl one in their heads causes an increase of the efficiency and a decrease of the effectiveness of adsorption at water–air interface, and that the standard free energy of adsorption can be predicted from the surface tension of the surfactants assuming the aryl group to be equivalent to 3.5 methylene groups. The experimentally obtained difference between the standard free energy of adsorption of the C12(EDMAB) and BDDAB was in good agreement with that theoretically accounted, corresponding to the standard free energy of adsorption of the aryl group. However, the best correlation between the values was obtained when a parallel orientation of the surfactant molecules at the adsorbed monolayer was taken into account.Introduction of the aryl group into the head of the surfactant (BDDAB) instead of the methyl one (C12(EDMAB)) causes the increase of the efficiency and decrease of the effectiveness of the BDDAB adsorption at water–air interface.
Keywords: Surfactants; Surface tension; Adsorption; Dodecylethyldimethylammonium bromide (C; 12; (EDMAB)); Benzyldimethyldodecylammonium bromide (BDDAB)
Magnetoviscosity of dilute suspensions of magnetic ellipsoids obtained through rotational Brownian dynamics simulations
by J.H. Sánchez; C. Rinaldi (pp. 500-506).
The magnetic field dependent viscosity (magnetoviscosity) of dilute suspensions of magnetic tri-axial ellipsoidal particles suspended in a Newtonian fluid and under applied shear and magnetic fields was studied numerically. Brownian dynamics simulations were performed to compute the intrinsic magnetoviscosity of the suspension. Results are presented for the response of dilute suspensions of ellipsoidal particles to constant magnetic and shear flow fields. Suspensions of ellipsoidal particles show a significant effect of aspect ratio on the intrinsic magnetoviscosity of the suspension, and this effect is more pronounced as the aspect ratio becomes more extreme. The use of an effective rotational diffusion coefficientDr,eff collapses the normalized intrinsic magnetoviscosity of all suspensions to a master curve as a function of Péclet number with the Langevin parameterα=(μ0μH)/(kBT) as parameter, up to a critical value of α for which the results for suspensions of spherical particles deviate from those of suspensions of ellipsoids. This discrepancy is attributed to the action of the shear-torque on the ellipsoidal particles, which tends to orient these particles in the direction of maximum deformation of the simple shear flow, and which does not act on spherical particles.The magnetoviscosity of dilute suspensions of magnetic tri-axial ellipsoidal particles suspended in a Newtonian fluid and under applied shear and magnetic fields was studied through rotational Brownian dynamics simulations.
Keywords: Magnetoviscosity; Rotational Brownian dynamics; Ellipsoid; Shear-torque
Behavior of fluorescent molecules bound to the interior of silica nanocapsules in various solvents
by Hirokazu Miyoshi; Yuki Matsuo; Yiyao Liu; Takao Sakata; Hirotaro Mori (pp. 507-513).
Porous silica nanocapsules with 20% 3-aminopropyltrimethoxysilane (APS)-bound 6-carboxy-fluorescein (APS-fluorescein) and 80% APS molecules adsorbed on the surface of a 50-nm-diameter Au core were prepared by a modified core–shell method. Silica mesoporous nanocapsules were obtained after the Au cores were dissolved in sodium cyanide. The size of the pores in the silica shells corresponded to the area of the fluorescein (approximately 1.02 nm2) in each APS-fluorescein molecule, which was bound to the silica shell by coupling between the silanol groups of APS in the APS-fluorescein molecule and the silica shell. The amino group of APS bound to the silica inside the shell is also reactive. Dy485XL N-hydroxysuccinimide ester (NHS) molecules were then added to the mesoporous silica nanocapsules in the solution and bonded to the amino group of the interior. Thus, mesoporous (fluorescein and Dy485XL)-bound silica nanocapsules were obtained. The fluorescence of Dy485XL was only observed in the mesoporous (fluorescein and Dy485XL)-bound silica nanocapsules in aqueous solution after ultrafiltration. However, the fluorescence of fluorescein reappeared after the addition of acetonitrile. Furthermore, upon adding various solvents to the mesoporous (fluorescein and Dy485XL)-bound silica nanocapsules, their fluorescence varied with that of fluorescein or Dy485XL. In the case of a mixture of 6-carboxy-fluorescein- N-hydroxysuccinimide (FLUOS) and Dy485XL-NHS free molecules in aqueous solution, the fluorescence of FLUOS was observed. Such different fluorescence phenomena demonstrated that Dy485XL-NHS molecules can easily penetrate into the nanocapsule interior via the pores and that the interior of the silica nanocapsules can bind to Dy485XL molecules. These fluorescence behaviors are discussed in terms of fluorescence resonance energy transfer (FRET) and solvatochromism.Preparation of fluorescent molecules (FLUOS and Dy485XL) bound to the interior of silica nanocapsules and behavior of their fluorescence in various solvents was investigated.
Keywords: Silica nanocapsule; Interior; Mesoporous; Surface modification; Solvatochromism; FRET; Silica shell
Macroscopic properties and microstructure of HSA based organogels: Sensitivity to polar additives
by Markus Burkhardt; Stefka Kinzel; Michael Gradzielski (pp. 514-521).
Organogels can be formed by a large variety of different low molecular weight gelators. In our investigations we employed 12-hydroxy stearic acid (HSA) and studied its ability to gel various organic solvents, such as dodecane, paraffin oil, triglycerides, octyl palmitate, and silicone oil. Gelation typically occurs above a concentration of 0.1–0.8 wt% and the gelation concentration is related to the polarity of the oil. In a second part we investigated the influence of polar additives which can affect the gelation process due to their polar character. By doing so we varied largely the polarity conditions under which the gelation of the HSA occurs. The macroscopic gel properties were characterised by means of oscillatory rheology experiments, differential scanning calorimetry (DSC), and optical microscopy. The microstructure of the samples was studied by means of small-angle neutron scattering (SANS). The gelation of HSA mainly depends on the availability of free acidic and hydroxy groups for the formation of H-bonds. Accordingly the elastic properties and finally the gelation process become suppressed by the addition of polar additives such as alcohols. This effect depends just on the molar ratio of added alcohol and HSA, being independent of the length of the added alcohol. Evidently the added alcohol is competing for the H-bonding with the HSA and thereby effectively destroying the H-bonding necessary for the formation of the network-forming fibres. This finding is of importance for potential applications of such molecules as rheological modifiers in oil-based systems.
Keywords: Organogels; Hydroxy stearic acid (HSA); Rheology; SANS; Polar additives
Phase behavior of semifluorinated catanionic mixtures: Head group dependence and spontaneous formation of vesicles
by Elena Blanco; Ulf Olsson; Juan M. Ruso; Pablo C. Schulz; Gerardo Prieto; Félix Sarmiento (pp. 522-531).
Hexadecyltrimethylammonium bromide (C16TAB)–sodium perfluorooctanoate (C8FONa) and hexadecylpyridynium bromide (C16PyB)–C8FONa catanionic semifluorinated mixtures have been studied by conductivity, dynamic light scattering (DLS), cryo-transmission electron microscopy (cryo-TEM) and polarizing microscopy. The regular solution theory, applicable for a limited fluorinated molar ratio, does not predict long-range electrostatic interactions. The results are consistent with the fact that in the hydrogenated-rich region the interaction is attractive in both catanionic mixtures. The systems containing pyridinium headgroups were of the stronger interaction. A transition from micelles was found in both mixtures as a function of fluorinated molar ratio. Special attention was devoted to the effect of the head group in the system properties. The information related with the mean vesicle radius measured by DLS was compared with the vesicle size distribution as well as the elastic properties of the bilayer measured with cryo-TEM.
Keywords: Catanionic mixtures; Perfluorinated surfactants; Spontaneous vesicles; Cryo-TEM; Conductivity; Dynamic light scattering; Polarizing microscopy
Polyelectrolyte-linked film assemblies of nanoparticles and nanoshells: Growth, stability, and optical properties
by Anne A. Galyean; Robert W. Day; Justin Malinowski; Kevin W. Kittredge; Michael C. Leopold (pp. 532-542).
Multi-layer films of nanoparticles and nanoshells featuring various polymeric linkage molecules have been assembled and their optical properties characterized. The growth dynamics, including molecular weight effects, and stability of the various nanoparticle film constructions, using both single polymer as well as combinations of alternating charge polyelectrolytes as linking mechanisms, are presented. The polymeric linkers studied include poly-L-lysine, poly-L-arginine, poly(allylamine hydrochloride), and polyamidoamine dendrimers. Significantly air stable films were achieved with the use of multi-layered polymeric bridges between the nanoparticles and nanoshells. Optical sensitivity normally observed with these nanomaterials in solution was observed for their corresponding film geometries, with the nanoshell films exhibiting a markedly higher ability to report their local dielectric environment.Multi-layers of polyelectrolyte linking molecules provide necessary interparticle spacing for air-stable assemblies of both aqueous nanoparticles and nanoshells that are optically sensitive to changes in the local environments.
Keywords: Nanoparticles; Nanoshells; Film assemblies; Polymeric linkers; Surface plasmon band
Comparison of exclusion volume corrections to the Poisson–Boltzmann equation for inhomogeneous electrolytes
by L.B. Bhuiyan; C.W. Outhwaite (pp. 543-547).
Comparisons are made of exclusion volume corrections to the Poisson–Boltzmann equation for the electric double layer next to a charged electrode. The exclusion volume terms treated are based mainly on (i) Langmuir type theories and (ii) the Bogoliubov–Born–Green–Yvon integral equations. The Langmuir type theories are modified to incorporate a distance of closest approach to the charged surface for comparison purposes. The theories are applied to the spherical electric double layer around a large macroion and the planar electric double layer. At high surface charge steric effects dominate when the Langmuir theories predict saturation in the counterion profile at and near contact, while the Bogoliubov–Born–Green–Yvon based theories predict layering in the same profile.Electrode–ion singlet distribution functions in a planar electric double layer for a 1:1, 0.1 M restricted primitive model electrolyte at 0.16 C/m2 surface charge density.
Keywords: Electric double layer; Exclusion volume; Poisson–Boltzmann
Acceleration effect of sulfate ion on the dissolution of amorphous silica
by Shuqin Bai; Shinji Urabe; Yoshihiro Okaue; Takushi Yokoyama (pp. 551-554).
The dissolution rate of amorphous silica is enhanced by sulfate ions. The zeta potential for silica particles in Na2SO4 solution was lower than that in NaCl solution with the same ionic strength. These facts indicate that the specific adsorption of sulfate ions occurred by overcoming repulsion between negative charges of the SO2−4 ion and SiO− on the surface of silica. The dissolution rate of amorphous silica may be accelerated by the specific adsorption of SO2−4 ions because of a decrease in the strength of theSiOSi bond in amorphous silica due to donation of electron density from the adsorbed SO2−4 ions.The dissolution of amorphous silica is accelerated by specific adsorption of sulfate ion on the surface of silica. (▴) Pure water. (●) 0.3 M sodium chloride. (■) 0.1 M sodium sulfate.
Keywords: Silica; Dissolution constant; Zeta potential; Specific adsorption; Effect of sulfate ion
Crown-forming instability phenomena in the drop splash problem
by Rouslan Krechetnikov; George M. Homsy (pp. 555-559).
The objective of this work is to study the fundamental instability behind the crown formation in the problem of drop splashing on a pre-existing liquid film. Based on experimental and theoretical insights, we demonstrate that the most plausible instability mechanism is of the Richtmyer–Meshkov type associated with a nearly impulsive acceleration of the interface. We also discover frustration phenomena in the wave number selection of the crown spike structure and study the corresponding bifurcation picture.Drop splash on a liquid film: Three modes of a crown formation.
Keywords: Drop splash; Crown formation; Rim instability; Frustration phenomena
Biscationic bicephalic (double-headed) amphiphiles with an aromatic spacer and a single hydrophobic tail
by Karolina Z. Roszak; Stephanie L. Torcivia; Kristina M. Hamill; Addie R. Hill; Kristen R. Radloff; David M. Crizer; Angela M. Middleton; Kevin L. Caran (pp. 560-564).
We report the synthesis and aggregation studies of a homologous family of biscationic “bicephalic” amphiphiles. Each of has a linear alkoxy chain and two trimethylammonium bromide headgroups connected to a benzene ring. Krafft temperatures (TK) in water were determined by differential scanning calorimetry (DSC) and conductivity. Critical micelle concentration (cmc) and ionization degree ( α) values were determined by monitoring the conductivity of aqueous solutions as a function of concentration, and confirmed by monitoring the1H NMR chemical shift of the terminal methyl group as a function of concentration. Values for log(cmc) decrease linearly with increasing chain length, with a smaller dependence on chain length than for single-headed amphiphiles, consistent with literature reports on other bicephalic amphiphiles. Comparison to two related amphiphiles, each with a single headgroup reveals that the addition of a second head group results in an increase in cmc and a decrease ofTK. These effects are attributed to greater water solubility due to the incorporation of a second, hydrophilic headgroup. The effect on α is also discussed.A family of novel amphiphiles with two head groups and a single linear hydrophobe (10–18 carbons) has been prepared and studied. Krafft temperature and critical micelle concentrations are reported.
Keywords: Double-headed amphiphile; Micelle; Critical micelle concentration (cmc); Krafft temperature; Ionization degree; Conductivity; Nuclear magnetic resonance (NMR) spectroscopy; Differential scanning calorimetry (DSC)