Journal of Colloid And Interface Science (v.310, #2)
Removal of chromate from water by a new CTAB–silica gelatin composite
by Francesco Venditti; Andrea Ceglie; Gerardo Palazzo; Giuseppe Colafemmina; Francesco Lopez (pp. 353-361).
A novel composite able to remove hexavalent chromium Cr(VI) from aqueous solutions was obtained by adding the silica precursor tetraethoxysilane (TEOS) to the hexadecyltrimethylammonium bromide (CTAB) microemulsion-based gel. A physical characterization of the new matrix revealed high stability of the silica gelatin composite in water at high temperatures and at neutral pH. Good efficiency in removing chromate from neutral solutions was also demonstrated by the adsorption kinetics. In particular, the adsorption data of chromate obtained with the CTAB–silica gelatin composite at 25 °C and pH 7.5 are described by the Freundlich isotherm model. The specific role of CTAB in the silica gelatin composite was also evaluated by comparing the kinetics of the anionic AOT–silica gelatin composite to the CTAB one. The data collected clearly showed that the positively charged surfactant was necessary to efficiently adsorb Cr(VI) from aqueous solutions. SEM and pulsed gradient spin–echo NMR analysis of the composite demonstrated that the silicon is well assembled in the gelatin network, in which water molecules maintain a high mobility. The diffusion coefficient of water in this system was shown to remain close to the value of pure water. Finally, X-ray analyses of the elemental content in the CTAB–silica gelatin composite indicated no difference in terms of percentage of silica distributions in different areas of the matrix and suggested that chromium adsorption could take place in internal areas.The adsorption isotherm of chromate obtained with the CTAB–silica gelatin composite at 25 °C pH 7.5.
Keywords: Organogel; Silica; Microemulsion; Chromate; Adsorption; Isotherm
Adsorption of toxic organic compounds from water with hydrophobic silica aerogels
by Suzana Štandeker; Zoran Novak; Željko Knez (pp. 362-368).
Silica monolith aerogels with different degrees of hydrophobicity were prepared by incorporating methyltrimethoxysilane (MTMS) or trimethylethoxysilane (TMES) in standard sol–gel synthesis followed by supercritical drying of gels with carbon dioxide (CO2) at 40 °C and 100 bar. The hydrophobicity of the aerogels was tested by measuring the contact angle ( θ). The aerogels were also characterised by FTIR, DSC, and porosity measurements. Adsorption capacity measurements show that such modified hydrophobic silica aerogels are excellent adsorbents for different toxic organic compounds from water. In comparison to granulated active carbon (GAC) they exhibit capacities which are from 15 to 400 times higher for all tested compounds. Adsorption properties of hydrophobic silica aerogel remain stable even after 20 adsorption/desorption cycles.The improved performance in adsorptivity of hydrophobic silica aerogel adsorbents over GAC, successful regeneration and repeated use make aerogels competitive to GAC for large-scale VOCs trapping and solvent clean-up applications.
Keywords: Hydrophobic silica aerogels; Sol–gel synthesis; Supercritical carbon dioxide drying; Adsorption; Volatile organic compounds
Adsorption of organic probes on silica through Lewis interactions: A comparison of experimental results and quantum chemical calculations
by B. Granqvist; T. Sandberg; M. Hotokka (pp. 369-376).
The adsorption of organic probe molecules on a partly dehydroxylated silica (SiO2) surface has been studied in a non-aquatic and non-polar environment. These results were compared to, verified and explained by quantum chemical calculations on the same systems. Since the systems are water free and since the non-polar solvent cyclohexane is used in the experiments, the quantum chemical calculations are well comparable to the experimental results without any additional terms. The characterized surface was found to contain both Lewis acid and Lewis base sites and a good agreement between the experimentally determined and the calculated data was found.The adsorption of organic probe molecules has been studied in a non-aquatic and non-polar environment. These results were compared to, verified and explained by quantum chemical calculations on the same systems. Since the systems are water free and since the non-polar solvent cyclohexane is used in the experiments, the quantum chemical calculations are well comparable to the experimental results without any additional terms.
Keywords: Adsorption; Quantum chemical calculations; Lewis acid; Lewis base; Silica; Probe molecules
A model for the cooperative adsorption of surfactant mixtures on solid surfaces
by Rui Zhang; Chi Liu; P. Somasundaran (pp. 377-384).
Adsorption of surfactant mixtures on solids is of considerable theoretical and practical importance. In this study, cooperative adsorption of surfactant mixtures of nonyl phenol ethoxylated decyl ether (NP-10) and n-dodecyl- β-D-maltoside (DM) on silica and alumina has been investigated as a function of the distribution of individual surfactants between solution and solid surface. In the mixed adsorption process, DM is identified to be the “active” adsorbing component and NP is the “passive” co-adsorbing one in the process of adsorption on alumina, while their roles are reversed on silica. A modified model has been proposed to quantify the adsorption behavior of surfactant mixtures and to obtain information in terms of aggregation number and standard free energy for surface aggregation. This model is the first model applied to the aggregation of the surfactant mixture at the solid/solution interfaces.The objective of this study was to develop a simple mathematic model to simulate the cooperative adsorption isotherm of surfactant mixtures on solid.
Attachment of nanoparticles to the AFM tips for direct measurements of interaction between a single nanoparticle and surfaces
by Quy K. Ong; Igor Sokolov (pp. 385-390).
Here we report a universal method of attachment/functionalization of tips for atomic force microscope (AFM) with nanoparticles. The particles of interest are glued to the AFM tip with epoxy. While the gluing of micron size particles with epoxy has been known, attachment of nanoparticles was a problem. The suggested method can be used for attachment of virtually any solid nanoparticles. Approximately every other tip prepared with this method has a single nanoparticle terminated apex. We demonstrate the force measurements between a single∼50nm ceria nanoparticle and flat silica surface in aqueous media of different acidity (pH 4–9). Comparing forces measured with larger ceria particles (∼500nm), we show that the interaction with nanoparticles is qualitatively different from the interaction with larger particles.
Keywords: Atomic force microscopy; Intermolecular interactions; Nanoparticles
Adsorption of carbon dioxide of 1-site and 3-site models in pillared clays: A Gibbs ensemble Monte Carlo simulation
by Xuan Peng; Jinsong Zhao; Dapeng Cao (pp. 391-401).
Adsorption behavior of carbon dioxide confined in pillared clays is analyzed by using constant pressure Gibbs ensemble Monte Carlo (GEMC) method. In our simulation, 1-site and 3-site models are used to represent carbon dioxide. At the 1-site model, carbon dioxide is described as a Lennard–Jones (LJ) sphere, while at the 3-site model, carbon dioxide is modeled as a three-sites linear chain represented by EPM2 potential considering the quadrapolar effect. The potential model from Yi et al. for pillared clays is used to emphasize its quasi two-dimensional structure. Comparing the calculated results from the 1-site and the 3-site models atT=228.15 and 258.15 K, we observe that the adsorption amount from the two models is the same basically. However, the local density presents a significant difference, because the shoulder in the main peak near the wall from 3-site model can reflect the orientation of carbon dioxide. Accordingly, in the systematical investigation to explore the effect of porosity and pore width on the adsorption of carbon dioxide in pillared clays, the 3-site model was only used. We observe that for a narrow pore ofH=1.02nm, each isotherm shape displays type I curve, suggesting that it is not inflected by the porosity. However, for the larger pores ofH=1.70 andH=2.38nm, the increase of the porosity alters the shape of adsorption isotherms from a simple linear relation to the first order jump, indicating that the porosity is of very important factor to affect adsorption and phase behavior of fluids confined in pillared clays. The excess adsorptions of carbon dioxide at supercritical temperatures ofT=323.15 and 348.15 K are also investigated. We find that the maximum exists for each excess isotherm, and the optimal pressure corresponding to the maximum increases with the pore width. However, the porosity has no significant effect on the optimal pressure.A Gibbs ensemble Monte Carlo simulation was used to investigate adsorption of carbon dioxide of 1-site and 3-site models in pillared clays, and the effects of pore width and porosity on adsorption of carbon dioxide were explored.
Keywords: Adsorption; Carbon dioxide; Pillared clay; Gibbs ensemble Monte Carlo simulation
Protolytic behavior of hydroxylated Pyrex glass surfaces in NaCl media
by Mauro Iuliano; Liberato Ciavatta; Gaetano De Tommaso (pp. 402-410).
Adsorption of hydrogen ions from aqueous NaCl solutions at the Pyrex glass–water interface was investigated by acid–base titration (glass electrode) at 25 °C and at the ionic strengths 0.010, 0.030, 0.10, 1.0, and 3.0 mol dm−3. The pH values ranged from 2 to 7. The Pyrex samples had a specific surface area of19.2×103m2kg−1 and a porous structure (pores 2.4 nm thick, 280 nm long). The reactions were found to be extremely slow but showed good reversibility. The potentiometric data, due to the small effect of ionic strength on the equilibria, were fitted with a simple nonelectrostatic model based on strong specific interactions of medium ions with deprotonated silanol, >SiO−, and boranol, >BO−, as well as with protonated sites. The acid–base properties are described by the reactions and equilibrium constants at the infinite dilution reference state: >SiONa + H+ ⇄ >SiOHNa+,logβ110Si=3.1±0.2; >SiONa + 2H+ + Cl− ⇄ >SiOH2Cl + Na+,logβ201Si=6.75±0.15; >SiONa + H+ ⇄ >SiOH + Na+,logβ100Si=1.8±0.2, >BONa + H+ ⇄ >BOH + Na+,logβ100B=6.4±0.2; >BONa + H+ ⇄ >BOHNa+,logβ110B=6.6±0.2; >BONa + 2H+ ⇄ >BOH+2 + Na+,logβ200B=11.56±0.15.Adsorption of hydrogen ions from aqueous NaCl solutions at the Pyrex glass–water interface was investigated by acid–base titrations.The acid–base properties are described by equilibrium constants.
Keywords: Pyrex glass; Adsorption; Acid–base properties; Equilibrium constants; Silanol and boranol sites; Potentiometric titration
Adsorptive accumulation of Cd(II), Co(II), Cu(II), Pb(II), and Ni(II) from water on montmorillonite: Influence of acid activation
by Krishna G. Bhattacharyya; Susmita Sen Gupta (pp. 411-424).
The present work investigates the influence of acid activation of montmorillonite on adsorption of Cd(II), Co(II), Cu(II), Ni(II), and Pb(II) from aqueous medium and comparison of the adsorption capacities with those on parent montmorillonite. The clay–metal interactions were studied under different conditions of pH, concentration of metal ions, amount of clay, interaction time, and temperature. The interactions were dependent on pH and the uptake was controlled by the amount of clay and the initial concentration of the metal ions. The adsorption capacity of acid-activated montmorillonite increases for all the metal ions. The interactions were adsorptive in nature and relatively fast and the rate processes more akin to the second-order kinetics. The adsorption data fitted both Langmuir and Freundlich isotherms, indicating that strong forces were responsible for the interactions at energetically nonuniform sites. The Langmuir monolayer capacity of the acid-activated montmorillonite is more than that of the parent montmorillonite (Cd(II): 32.7 and 33.2 mg/g; Co(II): 28.6 and 29.7 mg/g; Cu(II): 31.8 and 32.3 mg/g; Pb(II): 33.0 and 34.0 mg/g; and Ni(II): 28.4 and 29.5 mg/g for montmorillonite and acid-activated montmorillonite, respectively). The thermodynamics of the rate processes showed the adsorption of Co(II), Pb(II), and Ni(II) to be exothermic, accompanied by decreases in entropy and Gibbs free energy, while the adsorption of Cd(II) and Cu(II) was endothermic, with an increase in entropy and an appreciable decrease in Gibbs free energy. The results have established the potential use for montmorillonite and its acid-activated form as adsorbents for Cd(II), Co(II), Cu(II), Ni(II), and Pb(II) ions from aqueous media.Montmorillonite and acid-activated montmorillonite are used as adsorbents for Cd(II), Co(II), Cu(II), Ni(II), and Pb(II) in water at different pHs, concentrations, amounts of clay, times, and temperatures.
Keywords: Montmorillonite; Acid-activated montmorillonite; Adsorption kinetics; Adsorption isotherm; Temperature; Enthalpy; Metal ions
Sorption and binding of nanocrystalline gold by Merino wool fibres—An XPS study
by Michael J. Richardson; James H. Johnston (pp. 425-430).
Uniform, monodisperse gold nanocrystals have been adsorbed and chemically bound to Merino wool fibres, providing a permanent colouration through the interaction of visible light with the plasmon resonant modes of the nanocrystals. Surface analysis by X-ray photoelectron spectroscopy confirmed that the nanocrystalline gold was bound through the nitrogen of the amino groups on the surface of the gold to the keratin of the fibres. No shift in the absorptions attributed to the plasmon resonance modes of the nanocrystals were observed.Merino wool fibres (scanning electron image at ×100 magnification) bound via an amino nitrogen to a gold nanocrystal (inset).
Keywords: Wool; Keratin; Nanoparticle; ESCA; Gold
Adsorption of phenol and benzyl alcohol onto surfactant modified silica
by Geir Martin Førland; Anne Marit Blokhus (pp. 431-435).
The adsorption of the surfactant, dodecyltrimethylammonium bromide, DTAB, and the co-adsorption of the additives phenol and benzyl alcohol, onto silica from aqueous solutions are investigated. The adsorption of DTAB is found to increase with increasing alcohol concentration in solutions where the DTAB concentration is below the cmc. Moreover, the corresponding adsorption of DTAB decreases when the DTAB concentration is above the cmc. The co-adsorption of the alcohol is found to increase with increasing alcohol concentration, and benzyl alcohol co-adsorbs more strongly than phenol. The surfactant modified silica shows a very high ability to incorporate phenol and benzyl alcohol. The results are discussed in relation to solubilization site and surfactant aggregate shape.The work treats adsorption of DDAB and benzyl alcohol or phenol onto highly porous silica. The adsorption density of the surfactant increases upon increasing alcohol content in solutions below the cmc and decreases in solutions above the cmc. The corresponding adsorption of alcohol increases throughout the investigated region.
Keywords: Adsorption; Co-adsorption; Solubilization; Critical micelle concentration
Mitochondrial creatine kinase adsorption to biomimetic membranes: A Langmuir monolayer study
by Nathalie Vernoux; Ofelia Maniti; Françoise Besson; Thierry Granjon; Olivier Marcillat; Christian Vial (pp. 436-445).
Interaction of mitochondrial creatine kinase (mtCK) with either synthetic or natural zwitterionic or acidic phospholipids was monitored by surface pressure measurements. Injection of mtCK beneath a monolayer at very low surface pressure results in a large increase in the apparent area per lipid molecule reflecting the intrinsic surface activity of the protein. This effect is particularly pronounced with anionic phospholipid-containing films. Upon compression to high lateral pressure, the protein is squeezed out of the lipid monolayer. On the contrary, mtCK injected beneath a monolayer compressed at 30 mN/m, does not insert into the monolayer but is concentrated below the surface by anionic phospholipids as evidenced by the immediate and strong increase in the apparent molecular area occurring upon decompression. Below 8 mN/m the protein adsorbs to the interface and remains intercalated until the lateral pressure increases again. The critical pressure of insertion is higher for anionic lipid-containing monolayers than for films containing only zwitterionic phospholipids. In the former case it is markedly diminished by NaCl. The adsorption of mtCK depends on the percentage of negative charges carried by the monolayer and is reduced by increasing NaCl concentrations. However, the residual interaction existing in the absence of a global negative charge on the membrane may indicate that this interaction also involves a hydrophobic component.Mitochondrial creatine kinase interacts with anionic phospholipid-containing monolayers in a ionic strength sensitive manner. An hydrophobic component is also involved in this interaction.
Keywords: Mitochondrial creatine kinase; Langmuir monolayer; Dimyristoylphosphatidylcholine; Dimyristoylphosphatidylglycerol; Cardiolipin; Phosphatidylethanolamine; Elasticity coefficient; Protein lipid interaction
Synthesis of poly(ethylene glycol) (PEG)-grafted colloidal silica particles with improved stability in aqueous solvents
by Zhenkun Zhang; Anne E. Berns; Sabine Willbold; Johan Buitenhuis (pp. 446-455).
The known grafting procedures of colloidal silica particles with poly(ethylene glycol) (PEG) lead to grafting layers that detach from the silica surface and dissolve in water within a few days. We present a new grafting procedure of PEG onto silica with a significant improvement of the stability of the grafting layers in aqueous solvents. Moreover, the procedure avoids any dry states or other circumstances leading to strong aggregation of the particles. To achieve the improved water stability, Stöber silica particles are first pre-coated with a silane coupling agent (3-aminopropyl)triethoxysilane (APS) to incorporate active amine groups. The water solubility of the pre-coating layer was minimized using a combination of APS with bis-(trimethoxysilylpropyl)amine (BTMOSPA) or bis-(triethoxysilyl)ethane (BTEOSE). These pre-coated particles were then reacted with N-succinimidyl ester of mono-methoxy poly(ethylene glycol) carboxylic acid to form PEG-grafted silica particles. The particles form stable dispersions in aqueous solutions as well as several organic solvents.Colloidal silica particles were first pre-coated with a layer of low water solubility to obtain an improved water stability and then grafted with poly(ethylene glycol).
Keywords: PEG; Grafting; Colloidal silica; Water stability; Bridged silanes; 29; Si NMR
Evaluation on dispersion behavior of the aqueous copper nano-suspensions
by Xinfang Li; Dongsheng Zhu; Xianju Wang (pp. 456-463).
This paper presents a procedure for preparing a nanofluid which is solid–liquid composite material consisting of solid nanoparticles with sizes typically of 1–100 nm suspended in liquid. By means of the procedure, Cu–H2O nanofluids with and without dispersant were prepared, whose sediment photographs and particle size distribution were given to illustrate the stability and evenness of suspension with dispersant. Aiming at the dispersion of nano-Cu is regarded as the guide of heat transfer enhancement, the dispersion behavior of Cu nanoparticles in water were studied under different pH values, different dispersant types and concentration by the method of zeta potential, absorbency and sedimentation photographs. The results show that zeta potential has good corresponding relation with absorbency, and the higher absolute value of zeta potential and the absorbency are, the better dispersion and stability in system is. The absolute value of zeta potential and the absorbency are higher at pH 9.5. Hexadecyl trimethyl ammonium bromide (CATB) and sodium dodecylbenzenesulfonate (SDBS) can significantly increase the absolute value of zeta potential of particle surfaces by electrostatic repulsions, and polyoxyethylene (10) nonyl phenyl ether (TX-10) can form a thick hydration layer on the particle surfaces by steric interference, which leads to the enhancement of the stability for Cu suspensions. In the 0.1% copper nano-suspensions, the optimizing concentrations for TX-10, CATB, and SDBS are 0.43, 0.05, and 0.07%, respectively, which have the best dispersion results.The figure presents the zeta potential values of Cu–H2O suspensions with different dispersants at different pH values. According to the zeta potential values of copper powders, pH 9.5 can be selected as an operating pH.
Keywords: Copper nano-suspensions; Dispersion and stability; Zeta potential; Absorbency
Ultrafine biocompatible chitosan nanoparticles encapsulating multi-coloured quantum dots for bioapplications
by Wee Beng Tan; Ning Huang; Yong Zhang (pp. 464-470).
Owing to their excellent optical properties, luminescent semi-conductor quantum dots (QDs) have proven themselves to be an attractive choice in biological labeling. However, there exists the concern of cytotoxicity in using these heavy metal-based nanoparticles as molecular probes. In order to improve their general biocompatibility, CdSe/ZnS QDS are encapsulated in the natural biopolymer chitosan, forming monodisperse chitosan nanoparticles in the range of 60 nm in 1 single step. This straight forward method also allows for the synthesis of chitosan nanoparticles encapsulating multi-coloured QDs. In vitro 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity tests on primary myoblast cells suggest that the cytotoxicity of the QDs is greatly reduced after chitosan encapsulation. At the same time, fluorescence confocal microscopy studies also prove that nanoparticles are small enough to be internalized into the myoblast cells. Our results show the ease of synthesizing biocompatible, nanometer-sized chitosan nanoparticles encapsulating QDs and their promise in biological applications such as ultra-sensitive bio-detection and labeling of biomolecules.A straight-forward and easy method has been developed to prepare ultrafine biocompatible chitosan nanoparticles encapsulating multi-colour QDs. Essentially, green and red-fluorescing QDs at pre-determined molar ratios are encapsulated into chitosan nanoparticles to produce bar-coding fluorescent labels.
Keywords: Nanoparticles; Quantum dot; Multi-color; Chitosan
Aggregation kinetics of latex microspheres in alcohol–water media
by G. Odriozola; A. Schmitt; J. Callejas-Fernández; R. Hidalgo-Álvarez (pp. 471-480).
We report zeta potential and aggregation kinetics data on colloidal latex particles immersed in water–alcohol media. Zeta potential values show absolute maxima for volume fractions of alcohol of 0.10 and 0.05 for ethanol and 1-propanol, respectively. For methanol, no maximum of the absolute value of the zeta potential was found. Aggregation kinetics was studied by means of a single-cluster optical sizing equipment and for alcohol volume fractions ranging from 0 to 0.1. The aggregation processes are induced by adding different potassium bromide concentrations to the samples. We expected to find a slowdown of the overall aggregation kinetics for ethanol and 1-propanol, and no significant effect for methanol, as compared with pure water data. That is, we expected the zeta potential to govern the overall aggregation rate. However, we obtained a general enhancement of the aggregation kinetics for methanol and 1-propanol and a general slowdown of the aggregation rate for ethanol. In addition, aggregation data under ethanol show a slower kinetics for large electrolyte concentration than that obtained for intermediate electrolyte concentration. We think that these anomalous behaviors are linked to layering, changes in hydrophobicity of particle surfaces due to alcohol adsorption, complex ion–water–alcohol–surface structuring, and competition between alcohol–surface adsorption and alcohol–alcohol clustering.
Keywords: Aggregation kinetics; Binary mixtures; Polymer colloids; Colloidal stability; Alcohol–water mixtures
Responsive colloidal systems: Reversible aggregation and fabrication of superhydrophobic surfaces
by Mikhail Motornov; Roman Sheparovych; Robert Lupitskyy; Emily MacWilliams; Sergiy Minko (pp. 481-488).
We report on a method of fabricating stimuli-responsive core–shell nanoparticles using block copolymers covalently bound to a silica nanoparticle surface. We used the “grafting to” approach to graft amphiphilic block copolymer brushes of poly(styrene- b-2-vinylpyridine- b-ethylene oxide) and poly(styrene- b-4-vinylpyridine) onto silica nanoparticles with two different diameters: colloidal silica 200 nm in diameter and fumed silica 15 nm in diameter. We used the pH-responsive properties of the grafted brush to regulate the interactions between the particles, and between the particles and their environment. We show that this behavior can be applied for a reversible formation of particle aggregates, and can be used to tune and stabilize the secondary aggregates of particles of the appropriate size and morphology in an aqueous environment. The suspensions of the particles form a textured hydrophilic coating on various substrates upon casting and the evaporation of water. Heating above the polymer's glass transition temperature or treatment in acidic water result in back and forth switching between superhydrophobic and hydrophilic surfaces, respectively.Reversible aggregation of hybrid nanoparticles consisting of a silica core with a grafted responsive mixed-block copolymer brush shell.
Keywords: Coatings; Responsive colloids; Mixed polymer brushes; Ultrahydrophobic surface
Effect of hydrolyzable metal cations on the coagulation between hexadecane and mineral particles
by Mingli Cao; Weibing Gan; Qi Liu (pp. 489-497).
Mutual coagulation tests were conducted between hexadecane droplets (with and without doping with 0.001 mol/L sodium oleate) and micrometer-sized quartz, kaolinite, and illite particles in the presence and absence of multivalent hydrolyzable metal cations. It was observed that while hexadecane did not coagulate with quartz particles in the entire pH range tested (from 3 to 11), the presence of multivalent metal ions significantly increased the mutual coagulation between the hexadecane and quartz. And this only happened when the pH was raised to the level where first-order metal hydroxyl species and/or metal hydroxides were formed. The implications of this mutual coagulation for bitumen liberation from Alberta oil sands are discussed.Formation of first-order metal hydroxyl species significantly increased mutual coagulation between quartz particles and hexadecane oil droplets in aqueous solutions.
Keywords: Hexadecane; Quartz; Kaolinite; Illite; Multivalent metal cations; Coagulation; Liberation; Oil sands; Bitumen; Extraction
Comparative study for the removal of methylene blue via adsorption and photocatalytic degradation
by E.A. El-Sharkawy; Afaf Y. Soliman; Kawthr M. Al-Amer (pp. 498-508).
Physically and chemically activated carbons were prepared from date pits and olive stones. Titania and WO x-TiO2/MCM-41 were prepared as photoactive catalysts. Surface characterizations were investigated from ash content, pH, base neutralization capacities and FT-IR techniques. The textural characteristics, namely specific surface area (SBET) and pore texture, were determined from low temperature adsorption of N2 at 77 K. The decolorization of aqueous solution of methylene blue was performed by means of two alternative methods. Steam-activated carbons own higher surface area compared with ZnCl2-activated carbons, and the micropore surface area represents the major contribution of the total area. Steam-activated carbons were the most efficient decolorizing adsorbents owing to its higher surface area, total pore volume and the basic nature of the surface. The calculated values ofΔG0,ΔH0 andΔS0 indicate the spontaneous behavior of adsorption. The photocatalytic degradation is more convenient method in decolorizing of methylene blue compared with the adsorption process onto activated carbons.Adsorption/desorption isotherms of N2 adsorption onto activated carbons at 77 K.
Keywords: Activated carbons; Surface area; Pore texture; Methylene blue; XRD; Photocatalytic
Effect of deaeration on the adsorption of a mixture of cetyltrimethylammonium bromide and cetyldimethylbenzylammonium chloride at the mercury/electrolyte solution interface
by Antonis Avranas; Matilda Gernátová (pp. 509-518).
The effect of deaeration on the adsorption of a mixture of cetyltrimethylammonium bromide and cetyldimethylbenzylammonium chloride at the mercury/electrolyte interface solution is studied using capacitance measurements focusing mainly at very low temperatures. Isochronous capacitance vs potential curves reconstructed from capacitance time curves show that the deaeration depends on the type of inert gas used as well as the deaeration process. The deaeration changes mainly the kinetics of the change of the capacitance with time. In cases where a condensed film is formed, the equilibrium capacitance value does not change with deaeration, indicating that the organization of the surfactants at the interface is not connected with the deaeration. The effect is attributed to the removal of dissolved gases from water.The differences in the isochronous capacitance versus potential curves at 16.0 s show the effect of deaeration, the effect of the kind of inert gas used as well as the process.
Keywords: Cetyldimethylbenzylammonium chloride; Cetyltrimethylammonium bromide; Nitrogen; Helium; Deaeration time; Sparging time; Differential capacitance; Condensed film
Electrokinetic and surface chemical characterizations of an irradiated microfiltration polysulfone membrane: Comparison of two irradiation doses
by R. de Lara; J. Benavente (pp. 519-528).
The effect of ionizing radiation on the surface and electrokinetic characteristic parameters for a porous membrane of pore size 0.2 μm is determined and correlated with the irradiation dose (10 and 80 J/kg). Changes in NaCl permeability and membrane system electrical resistance determined from diffusion and impedance spectroscopy measurements are consistent with the increase of membrane pore radii/porosity, in agreement with SEM micrographs and reported results. Low irradiation dose seems to clean the membrane surface of impurities, according to XPS results, but the increase of irradiation doses could affect surface roughness. Due to the relatively high pore radius, ion transport numbers are practically independent of radiation and dose, but irradiation slightly modifies the membrane solution interface by increasing its weakly electronegative character, which could be of interest in the ultrafiltration of proteins or macromolecules.Effect of gamma irradiation on (a) membrane diffusional permeability; (b) zeta potential. (○) Original sample; (▵) 10 J/kg dose; (◊) 80 J/kg dose.
Keywords: Ionizing radiation treatment; Irradiation dose; XPS; Diffusional permeability; Impedance spectroscopy; Zeta potential
Controllable porous polymer particles generated by electrospraying
by Y.Q. Yiquan Wu; Robert L. Clark (pp. 529-535).
In this paper, an electrospraying technique was applied to prepare polycaprolactone (PCL) polymer particles with a different microstructure. The PCL particles can be controlled to have a porous microstructure by tailoring the evaporation of solvents during the electrospraying process. The effect of various concentrations on the morphology and microstructure of PCL particles was investigated. The experiment has demonstrated the versatile capability of the electrohydrodynamic atomization process for preparing polymer PCL porous particles and fibers. The thermally induced and evaporation-induced phase separations are proposed as the main mechanisms for the porous microstructure formation. The results demonstrate that the electrospraying method is a simple, innovative and cost-effective method for preparing polymer particles with controllable microstructures.The electrospraying is an innovative and cost-effective method for preparing polymer particles with controllable porous microstructure through phase separation by tailoring the evaporation of solvents during the process.
Keywords: Electrospraying; Polymer particles; Electrospinning
Use of different types of mesoporous materials as tools for organic synthesis
by Tomasz Witula; Krister Holmberg (pp. 536-545).
Mesoporous materials have been investigated as auxiliary agents for organic synthesis comprising reactants with widely different solubility characteristics. The finely divided oxide material was immersed in an aqueous solution of a water-soluble reactant, potassium iodide, and the loaded particles were kept under stirring in the hydrophobic reactant, 4- tert-butylbenzyl bromide, or in a hydrocarbon solution of this reactant. The reaction proceeded well in alumina and silica of either bicontinuous cubic or hexagonal geometry. It was shown for silica that the particle size was an important parameter; the smaller the size the faster the reaction. Titania gave a much lower reaction rate than alumina and silica. It was found that the hexagonal mesoporous alumina could be reused either as a slurry or in a column procedure. Attempts were also made to use hydrophobic mesoporous materials, either mesoporous graphite or mesoporous oxide treated with chlorotrimethylsilane, in the reversed mode. The hydrophobic solid was then immersed in a solution of the hydrophobic reactant and subsequently dispersed in an aqueous solution of the water-soluble reactant. Two nucleophilic substitution reactions and one oxidation reaction were investigated but the yields were low in all cases.
Keywords: Mesoporous material; Liquid crystal; Microemulsion; Organic synthesis; Nucleophilic substitution
Experimental investigation on bubble coalescence under nonuniform temperature distribution in reduced gravity
by Q. Kang; H.L. Cui; L. Hu; L. Duan; W.R. Hu (pp. 546-549).
Results on bubble coalescences from the space experiment of thermocapillary bubble migration conducted on board the Chinese 22nd recoverable satellite are presented in this paper. Some coalescences of large spherical bubbles under microgravity are observed through bubbles staying at the upper side of the test cell. The data of bubble coalescence time are recorded and compared with theoretical predictions, which is based on a theory to describe the tendency of coalescence connected to chemical potential difference. It is implied that the theory is applicable for the experimental data of bubble coalescence. Moreover, the angle between the line of two bubble centers and temperature gradient falled mostly in the range 20°–40°.Results on bubble coalescences from the space experiment of thermocapillary bubble migration conducted on board the Chinese 22nd recoverable satellite are presented.
Keywords: Bubble; Coalescence; Microgravity; Temperature gradient
Surface treatment and characterization of ITO thin films using atmospheric pressure plasma for organic light emitting diodes
by Mi-Hee Jung; Ho-Suk Choi (pp. 550-558).
Ar atmospheric pressure plasma (APP) was used to treat indium-tin-oxide (ITO). The plasma conditions were varied to treat the ITO surface, e.g., plasma treatment time, RF power, flow rate, and the plasma outlet-to-sample distance. The plasma effectiveness was measured by the contact angle. The change in the surface energy calculated with the Owens–Wendt method mainly arises from the polar component. The dynamic contact angle measurements show that APP-treated surface showed considerably lower hysteresis in the water and ethylene glycol but there was no change in hysteresis in methylene iodide compared with the untreated ITO. Atomic force microscopy showed that the Ar APP-treated surface sharply decreased the surface roughness and showed a similar morphology as the untreated ITO. X-ray photoelectron spectroscopy showed that the Ar APP treatment not only effectively removed carbon contamination from the surface but also introduced oxygen. Therefore, it is believed that the APP treatment modifies the physico-chemical properties of ITO, which can in turn improve the performance of the organic light-emitting diodes.Atomic force microscopy showed that the Ar APP-treated surface sharply decreased the surface roughness and showed a similar morphology as the untreated ITO. (a) Untreated ITO, (b) O2 LPP, (c) Ar/O2 APP, (d) Ar APP.
Keywords: Atmospheric pressure plasma; Low pressure plasma; Indium-tin-oxide; Contact angle; Hysteresis; Surface free energy; Atomic force microscopy; X-ray photoelectron spectroscopy; Organic light-emitting diodes
Generation and characterization of surface layers on acoustically levitated drops
by Rudolf Tuckermann; Sigurd Bauerecker; Heiko K. Cammenga (pp. 559-569).
Surface layers of natural and technical amphiphiles, e.g., octadecanol, stearic acid and related compounds as well as perfluorinated fatty alcohols (PFA), have been investigated on the surface of acoustically levitated drops. In contrast to Langmuir troughs, traditionally used in the research of surface layers at the air–water interface, acoustic levitation offers the advantages of a minimized and contact-less technique. Although the film pressure cannot be directly adjusted on acoustically levitated drops, it runs through a wide pressure range due to the shrinking surface of an evaporating drop. During this process, different states of the generated surface layer have been identified, in particular the phase transition from the gaseous or liquid-expanded to the liquid-condensed state of surface layers of octadecanol and other related amphiphiles. Characteristic parameters, such as the relative permeation resistance and the area per molecule in a condensed surface layer, have been quantified and were found comparable to results obtained from surface layers generated on Langmuir troughs.Monomolecular surface layers of different natural and technical amphiphiles have been successfully generated and characterized on acoustically levitated water drops, introducing this technique as a promising tool to interface sciences.
Keywords: Acoustic levitation; Surface layer; Natural and technical amphiphiles; Permeation resistance
Emulsification in turbulent flow:
by Slavka Tcholakova; Nina Vankova; Nikolai D. Denkov; Thomas Danner (pp. 570-589).
Systematic set of experiments is performed to clarify the effects of several factors on the size distribution of the daughter drops, which are formed as a result of drop breakage during emulsification in turbulent flow. The effects of oil viscosity,ηD, interfacial tension, σ, and rate of energy dissipation in the turbulent flow, ε, are studied. As starting oil–water premixes we use emulsions containing monodisperse oil drops, which have been generated by membrane emulsification. By passing these premixes through a narrow-gap homogenizer, working in turbulent regime of emulsification, we monitor the changes in the drop-size distribution with the emulsification time. The experimental data are analyzed by using a new numerical procedure, which is based on the assumption (supported by the experimental data) that the probability for formation of daughter drops with diameter smaller than the maximum diameter of the stable drops,d
Keywords: Drop breakage; Emulsification in turbulent flow; Drop-size distribution; Daughter drops; Satellite drops
A novel method to quantify the amount of surfactant at the oil/water interface and to determine total interfacial area of emulsions
by Monica A. James-Smith; Kile Alford; Dinesh O. Shah (pp. 590-598).
We present a methodology to quantitatively determine the fraction of sodium dodecyl sulfate (SDS) that partitions to the oil/water interface in oil-in-water macroemulsions and calculate the total interfacial area (TIA) through the novel use of filtration through nanoporous membranes. Ultrafiltration was carried out in centrifuge tubes having nanoporous filters with a 30,000 molecular weight cutoff (MWCO), so that emulsion droplets would not pass through, and only SDS (as monomers and micelles) that is in the bulk water phase (i.e., not at the interface) could pass through. The concentration of SDS in the filtrate was determined and used to calculate the TIA for each system. The mean droplet diameter of the emulsions was measured by light scattering. We analyzed the effects of total SDS concentration and oil chain length on the amount of SDS that partitions to the interface, the TIA, and the droplet diameter. The results showed that partitioning of SDS to the oil/water interface increases with increasing total SDS concentration in emulsion systems (i.e., the more SDS we add to the bulk solution, the more SDS partitions to the oil/water interface). However, the surface-to-bulk partition coefficient (i.e., the SDS concentration at the interface divided by the SDS concentration in the aqueous phase) remains the same over the entire concentration range (8–200 mM). The results showed a chain-length compatibility effect in that the minimum amount of SDS partitioned to the interface for C12 oil. The droplet size measurements revealed a maximum size of droplets for C12 oil. Penetration of oil molecules into SDS film at the interface has been proposed to account for the maximum droplet size and minimum partitioning of SDS at the oil/water interface for C12 oil+SDS emulsion system. The TIA, as determined from our ultrafiltration method, was consistently two orders of magnitude greater than that calculated from the droplet size measured by light scattering. Possible explanations for this disparity are discussed.Filtration of oil-in-water emulsion through a nanoporous filter membrane to determine the amount of surfactant that is at the interface and thereby determine the total interfacial area of the emulsion.
Keywords: Oil-in-water emulsion; Total interfacial area; Sodium dodecyl sulfate; Ultrafiltration; Partitioning; Effect of oil chain length; Effect of SDS concentration; Droplet size; Light scattering
Deformation and motion of a charged conducting drop in a dielectric liquid under a nonuniform electric field
by J.G. Kim; D.J. Im; Y.M. Jung; I.S. Kang (pp. 599-606).
As a tool for transporting a drop inside another fluid, a charged conducting drop driven by Coulombic force is considered. Specifically, deformation and motion of a charged conducting drop under nonuniform electric fields are studied using the perturbation method. For simplicity in analysis, the applied electric field is assumed to be expressed as the sum of a uniform field and a linear field and the flow is assumed to be in the Stokes flow range. The deformed drop shape due to electrical stress is computed to the first order of the electrical Weber number ( W). Then the electric force and the hydrodynamic drag are computed to derive the formula of the translation velocity, which is valid up toO(W). Several important results have also been obtained for the effect of drop deformation on the electric and hydrodynamic forces exerted on the drop.Periodically oscillating motion of a conducting drop under electric field in a dielectric liquid between two electrodes.
Keywords: Charged conducting drop; Drop deformation; Coulombic force; Dielectric force
Conditions for similitude and the effect of finite Debye length in electroosmotic flows
by Jung Min Oh; Kwan Hyoung Kang (pp. 607-616).
Under certain conditions, the velocity field is similar to the electric field for electroosmotic flow (EOF) inside a channel. There was a disagreement between investigators on the necessity of the infinitesimal-Reynolds-number condition for the similarity when the Helmholtz–Smoluchowski relation is applied throughout the boundaries. What is puzzling is a recent numerical result that showed, contrary to the conventional belief, an evident Reynolds number dependence of the EOF. We show here that the notion that the infinitesimal-Reynolds-number condition is required originates from the misunderstanding that the EOF is the Stokes flow. We point out that the EOF becomes the potential flow when the Helmholtz–Smoluchowski relation is applied at the boundaries. We carry out a numerical simulation to investigate the effect of finiteness of the Debye length and the vorticity layer inherently existing at the channel wall. We show that the Reynolds number dependence of the previous numerical simulation resulted from the finiteness of the Debye length and subsequent convective transport of vorticity toward the bulk flow. We discuss in detail how the convection of vorticity occurs and what factors are involved in the transport process, after carrying out the simulation for different Reynolds numbers, Debye lengths, corner radii, and geometries.The breakdown of similarity and the Reynolds number dependence of electroosmotic flows result from the finiteness of Debye length and the subsequent convective transport of vorticity toward the bulk flow.
Keywords: Electroosmotic flow; Similarity; Similitude; Reynolds number dependence; Vorticity; Convection; Numerical analysis
Rheology and UV-protecting properties of complex suspensions of titanium dioxides and zinc oxides
by Akio Nasu; Yasufumi Otsubo (pp. 617-623).
Ultra-fine particles of titanium dioxide (TiO2) and zinc oxides (ZnO) are very attractive as UV-protecting ingredients in cosmetic products. The UV-scattering behavior of complex suspensions in a silicone oil is studied in relation to rheological properties. To control the dispersion stability of suspensions, three polyoxyethylene (POE)-modified silicones of branch-type, (AB) n-type, and ABA-type are used as dispersants. Irrespective of molecular structure, the dispersants can stabilize the TiO2 and ZnO particles and the flow of both single suspensions is Newtonian with low viscosity. However, the Newtonian flow profiles and high dispersion states are maintained only for complex suspensions prepared with ABA-type dispersant. Since the POE groups which are incorporated between terminal silicones groups attach to the particle surfaces, the steric stabilization is responsible for low viscosity and high dispersions. Because the UV scattering of suspensions is determined by the sizes of flocculated structures, the high transmittance in the visible ranges and low transmittance in the UVA and UVB ranges can be achieved in the presence of ABA-type dispersant.The complex suspensions of TiO2 and ZnO particles, the transmittance of which is high in the visible range and low in the UVA and UVB ranges, can be formulated by the use of ABA-type polyoxyethylene (POE)-modified silicone dispersant.
Keywords: Polyoxyethylene-modified silicones; Suspension rheology; Titanium dioxide; UV-protecting ability; Zinc oxide
Rheological characterisation of bis-urea based viscoelastic solutions in an apolar solvent
by Guylaine Ducouret; Christophe Chassenieux; Sandrine Martins; François Lequeux; Laurent Bouteiller (pp. 624-629).
The rheological properties of hydrogen bonded reversible aggregates in apolar solvent have been investigated. The zero shear viscosity, the plateau modulus and the terminal viscoelastic relaxation time exhibit power laws dependencies with the concentration that have been compared with the behaviours expected for reversible polymers. It appears that the dynamics originate from scission/recombination mechanisms. Moreover, the growth of the aggregates with concentration follows the laws observed and predicted for worm-like micelles at low concentrations allowing the length of the aggregates to be estimated 500 nm at 3 g L−1. However, at the highest concentrations investigated, deviations from the power laws suggest the presence of some intrinsic chain stopper poisons in the solutions.When dissolved in apolar solvents, bis-urea self assemble into flexible filaments leading to viscoelastic solutions. Their dynamics originate from scission/recombination mechanisms like for surfactant-based worm-like micelles.
Keywords: Rheology; Self-assembly; Hydrogen bounding; Worm-like micelles; Equilibrium polymers; Bis-urea
Construction of higher-ordered monolayer membranes derived from archaeal membrane lipid-inspired cyclic lipids with longer alkyl chains
by Makoto Nakamura; Rie Goto; Toshio Tadokoro; Motonari Shibakami (pp. 630-642).
A series of artificial cyclic lipids that mimic archaeal membrane ones has been synthesized. The structural features of these molecules include a longer cyclic framework, in which the alkyl chain length ranges from 24 to 32 in carbon number, which is longer than our first analogous molecule with 20-carbon long alkyl chains [K. Miyawaki, T. Takagi, M. Shibakami, Synlett 8 (2002) 1326]. Microscopic observation reveals that these molecules have a self-assembling ability: hydration of the lipids yields multilamellar vesicles in aqueous solution and monolayer sheets on solid supports. High-sensitivity differential scanning calorimetry (24- and 28-carbon alkyl chain lipids) indicates that (i) the alkyl chain length affects their phase behavior and (ii) the enthalpies of endothermic peaks accompanied by phase transition were considerably lower than those of their monomeric phospholipid analogs. Fluorescence polarization measurements suggest that the membranes made from the 24-carbon alkyl chain lipid have a higher polarization factor than membranes composed of DMPC and DMPC plus cholesterol. These findings imply that the cyclic lipids containing 24- and 28-carbon alkyl chain construct well-organized monolayer membranes and, in particular, that the molecular order of the 24-carbon alkyl chain lipid is higher than that of bilayer membranes in the liquid-ordered phase.A series of artificial lipids featuring a cyclic framework have been synthesized. The results of DSC and fluorescence polarization measurements imply that the cyclic lipids construct well-organized monolayer membranes.
Keywords: Cyclic lipid; Archaeal membrane lipid; Higher-ordered monolayer; Self-assembly
Synthesis and characterization of the air–water interfacial TiO2/ZrO2 binary oxide film
by Chun Kan; Xiaoheng Liu; Guorong Duan; Xin Wang; Xujie Yang; Lude Lu (pp. 643-647).
TiO2/ZrO2 binary oxide film was self-assembled using anionic surfactant (sodium dodecyl sulfonate (SDS)) as template and obtained at the air–water interface. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to characterize the obtained film. The film was composed of many lamellar nanorods with a d spacing of 3.2 nm, and the lamellas were perpendicular to the lengthwise position of the rods. The energy-dispersive spectrum (EDS) was used for determining the titanium/zirconium atomic ratio. After being calcined, the sample decomposed to a mixture of anatase titania and tetragonal zirconia, and all the lamellar structure was broken.A TiO2/ZrO2 binary oxide film, composed of many lamellar nanorods, is self-assembled at the air–water interface using an anionic surfactant as a template.
Keywords: Titania; Zirconia; Self-assembly; Anionic surfactant; Lamellar structure; Air–water interface
Dewetting self-assembly of nanoparticles into hexagonal array of nanorings
by Nobuhiko J. Suematsu; Yumi Ogawa; Yasuhiko Yamamoto; Tomohiko Yamaguchi (pp. 648-652).
Nanoparticles self-assembled into ring-shaped aggregates that were arranged in a two-dimensional (2D) hexagonal pattern. This hierarchic pattern was prepared by casting a toluene solution composed of polystyrene (PS) and Ag nanoparticles (NP). Dewetting of the thin composite layer induced the mesoscopic hexagonal array of PS–NP droplets. Within each dried droplet (dot), Ag nanoparticles self-assembled into a spot- or a ring-shaped 2D superlattice alternatively depending on the size of the dot, which was controlled by the molecular weight of PS.Dissipative dewetting followed by self-assembly of nanoparticles (NP). The dewetting of polystyrene–nanoparticle (PS–NP) solution induces an ordered array of PS–NP droplets where self-assembly produces nanorings.
Keywords: Self-assembly; Nanoparticle; Dewetting; Self-organization; Nanoring; Bifurcation
Enantioselective crystallization of histidine on chiral self-assembled films of cysteine
by David H. Dressler; Yitzhak Mastai (pp. 653-660).
In this paper, the preparation and use of chiral surfaces derived from enantiomerically pure crystals of amino acids are described. For this purpose, a self-assembly process to grow thin chiral films of (+)-l- or (−)-d-cysteine on gold surfaces was chosen. These chiral films were utilized as crystallization catalysts in the crystallization of enantiomers from solutions. To demonstrate the chiral discrimination power of the chiral surfaces in crystallization processes, the crystallization of racemic histidine onto the chiral films was investigated. Our study demonstrates the potential application of chiral films to control chirality throughout crystallization, where one enantiomer crystallizes onto the chiral surfaces with relative high enantiomeric excess. In addition, crystallization of pure histidine enantiomers onto chiral films results in strong crystal morphology modification with preferred orientation.In this paper, we describe the preparation and use of chiral surfaces derived from enantiomerically pure crystals of amino acids. We utilized those chiral films as crystallization catalyst in the crystallization of enantiomers from solutions. Our study demonstrates the potential application of chiral films to control chirality throughout crystallization, where one enantiomer crystallized on the chiral surfaces with relatively high enantiomeric excess.
Keywords: Amino acids; Chirality; Chiral surfaces; Crystallization; Self-assembly; Thin films
Force measurements of bacterial adhesion on metals using a cell probe atomic force microscope
by Xiaoxia Sheng; Yen Peng Ting; Simo Olavi Pehkonen (pp. 661-669).
The adhesion of microbial cells to metal surfaces in aqueous media is an important phenomenon in both the natural environment and engineering systems. The adhesion of two anaerobic sulfate-reducing bacteria ( Desulfovibrio desulfuricans and a local marine isolate) and an aerobe ( Pseudomonas sp.) to four polished metal surfaces (i.e., stainless steel 316, mild steel, aluminum, and copper) was examined using a force spectroscopy technique with an atomic force microscope (AFM). Using a modified bacterial tip, the attraction and repulsion forces (in the nano-Newton range) between the bacterial cell and the metal surface in aqueous media were quantified. Results show that the bacterial adhesion force to aluminum is the highest among the metals investigated, whereas the one to copper is the lowest. The bacterial adhesion forces to metals are influenced by both the electrostatic force and metal surface hydrophobicity. It is also found that the physiological properties of the bacterium, namely the bacterial surface charges and hydrophobicity, also have influence on the bacteria–metal interaction. The adhesion to the metals by Pseudomonas sp. and D. desulfuricans was greater than by the marine SRB isolate. The cell–cell interactions show that there are strong electrostatic repulsion forces between bacterial cells. Cell probe atomic force microscopy has provided some useful insight into the interactions of bacterial cells with the metal surfaces.The adhesion forces for initial biofilm formation to the metal surfaces can be quantified by using AFM force measurement with a cell probe.
Keywords: Adhesion force; Atomic force microscopy; Sulfate-reducing bacteria; Cell probe; Pseudomonas; sp.; Desulfovibrio desulfuricans
Interaction between electrical double layers of soil colloids and Fe/Al oxides in suspensions
by Tao Hou; Renkou Xu; Diwakar Tiwari; Anzhen Zhao (pp. 670-674).
Phyllosilicates with net negative surface charge and Fe/Al oxides with net positive surface charge coexist in variable-charge soils, and the interaction between these oppositely charged particles affects the stability of mixed colloids, aggregation, and even the surface chemical properties of variable-charge soils. The interaction of the diffuse layers of electrical double layers between the negatively charged soil colloidal particles and the positively charged particles of goethite or γ-Al2O3 was investigated in this article through the comparison of zeta potentials between single-soil colloidal systems and binary systems containing soil colloids and Fe/Al oxides. The results showed that the presence of goethite and γ-Al2O3 increased the zeta potential of the binary system containing soil colloids and Fe/Al oxides, which clearly suggests the overlapping of the diffuse layers in soil colloids and Fe/Al oxides. The overlapping of the diffuse layers leads to a decrease in the effective negative charge density on soil colloid and thus causes a shift of pH–zeta potential curves toward the more positive-value side. The interaction of the electrical double layers is also related to the charge characteristics on the Fe/Al oxides: the higher the positive charge density on Fe/Al oxides, the stronger the interaction of the electrical double layers between the soil colloid particles and the Fe/Al oxides.The presence of goethite and γ-Al2O3 increased the zeta potential of the binary system containing soil colloid and Fe/Al oxides, which suggests the overlapping of the diffuse layers of electrical double layers in soil colloids and Fe/Al oxides.
Keywords: Zeta potential; Electrical double layer; Interaction of diffuse layers; Variable-charge soil; Constant-charge soil; Goethite; γ; -Al; 2; O; 3
Comments on the conditions for similitude in electroosmotic flows
by Juan G. Santiago (pp. 675-677).
This note provides a few comments on the conditions required for similitude between velocity and electric field in electroosmotic flows. The velocity fields of certain electroosmotic flows with relatively thin electric double layers (EDLs) are known to be irrotational in regions outside of the EDL. Under restricted conditions, the velocity field,V¯, can be expressed in terms of the electric field,E¯, asV¯=cE¯, where c is a scalar constant. The irrotationality solution is certainly unique and exact for Stokes flow, but may not be stable (or unique) for flows with Reynolds numbers significantly greater than unity.
Keywords: Electrokinetics; Electroosmosis; Similitude; Microfluidics; Irrotational; Vorticity
Characterization of chitosan nanofiber fabric by electrospray deposition: Electrokinetic and adsorption behavior
by Hidetoshi Matsumoto; Hiroshi Yako; Mie Minagawa; Akihiko Tanioka (pp. 678-681).
Cationic biopolymer nanofiber fabrics were prepared from a chitosan/poly(ethylene oxide) blend solution by electrospray deposition. Their electrokinetic properties and DNA adsorption behavior were analyzed as a function of pH. The zeta potential was determined from streaming potential/streaming current measurements. The adsorption of DNA onto the fabrics was investigated by spectrophotoscopy. The adsorption behavior of DNA correlated well with the electrokinetic properties of the fabrics. This revealed that the electrokinetic approach was a useful option for characterization of novel nanofiber assemblies made by the electrostatic spray process. In addition, these results provided fundamental information about chitosan nanofiber fabrics for both biomedical and analytical applications.Electrokinetic properties of the chitosan nanofiber fabrics made by the electrospray deposition were characterized by streaming potential/streaming current measurements. The adsorption behavior of DNA well correlated with the electrokinetic properties of the fabrics.
Keywords: Electrospray deposition; Nanofiber fabric; Chitosan; Zeta potential; Adsorption; DNA
Catalytic behavior of tris(2,2′-bipyridine)iron(II) complex in chemiluminescence reaction of luminol in reversed micellar medium of cetyltrimethylammonium chloride
by Terufumi Fujiwara; Imdad U. Mohammadzai; Keizo Kitayama; Yoshimoto Funazumi; Takahiro Kumamaru (pp. 682-685).
Tris(2,2′-bipyridine) complex of iron(II) was found to cause an increase in the chemiluminescence (CL) emission of luminol dispersed in the reversed micellar medium of cetyltrimethylammonium chloride (CTAC) in 1:1 (v/v) dichloromethane–cyclohexane/water, when the iron(II) complex in dichloromethane was mixed directly with the reversed micellar solution containing luminol. Visible absorption measurements showed that, when dispersed in the CTAC reversed micellar medium, the iron(II) complex dissociates easily. In the reverse micelle, subsequently the free iron(II) ion produced may catalyze the CL oxidation of luminol even in the absence of hydrogen peroxide. The CL emission produced under the optimized experimental conditions was detectable at a minimum iron(II) concentration of1.0×10−9 M using a flow injection system.A unique ability of the [Fe(bpy)3]2+ complex to enhance the luminol chemiluminescence following the dissociation of the complex into the iron(II) ion in the CTAC reverse micelle is demonstrated.
Keywords: Luminol chemiluminescence; Reversed micellar medium; Cetyltrimethylammonium chloride; Tris(2,2′-bipyridine)iron(II) complex; Dissociation
Efficient peroxide decoloration of azo dye catalyzed by polyethylene glycol-linked manganese chlorin derivative
by Masaharu Kondo; Tatsuro Mitsui; Shingo Ito; Yuji Kondo; Syuichi Ishigure; Takehisa Dewa; Keiji Yamashita; Junko Nakamura; Ritsuko Oura; Mamoru Nango (pp. 686-689).
We reported here that polyethylene glycol (PEG)-linked manganese pyrochlorophyllide a (PEG-MnPChlide a) possesses remarkable catalytic activity comparable to horseradish peroxidase (HRP). The PEG-MnPChlide a catalyzed the oxidation decoloration reaction of C.I. Acid Orange 7 by hydrogen peroxide under a mild aqueous condition, pH 8.0 at 25 °C. The manganese pyrochlorophyride a methylester (MnPChlide a ME) dissolved in a Triton X-100 micellar solution also exhibited the catalytic activity, indicating the micellar environment plays an important role in the catalytic reaction. The reaction rate was accelerated by addition of imidazole. The catalytic reactions were analyzed by Michaelis–Menten kinetics, revealing that the higher reactivity of catalyst–substrate complex is responsible for the present catalytic reaction system.
Keywords: Manganese chlorin derivative; Amphipathic polymer; Oxidation catalyst; Azo dye; Enzyme-like catalytic reaction