Journal of Colloid And Interface Science (v.302, #1)
Editorial Board (CO1).
New methodology to determine the rate-limiting adsorption kinetics mechanism from experimental dynamic surface tension data by Srinivas Nageswaran Moorkanikkara; Daniel Blankschtein (1-19).
We present a new methodology to determine the rate-limiting adsorption kinetics mechanism (diffusion-controlled vs mixed diffusion-barrier controlled), including deducing the kinetics parameters (the diffusion coefficient, D, and the energy-barrier parameter, β), from the experimental short-time dynamic surface tension (DST) data. The new methodology has the following advantages over the existing procedure used to analyze the experimental DST data: (a) it does not require using a model for the equilibrium adsorption isotherm, and (b) it only requires using the experimental short-time DST data measured at two initial surfactant bulk solution concentrations. We apply the new methodology to analyze the experimental short-time DST data of the following alkyl poly(ethylene oxide), C i E j , nonionic surfactants: C12E4, C12E6, C12E8, and C10E8 measured using the pendant-bubble apparatus. We find that for C12E4 and C12E6, the effect of the energy barrier on the overall rate of surfactant adsorption can be neglected for surfactant bulk solution concentrations below their respective critical micelle concentrations (CMCs), and therefore, that the rate-limiting adsorption kinetics mechanism for C12E4 and C12E6 is diffusion-controlled at any of their premicellar surfactant bulk solution concentrations. On the other hand, for C12E8 and C10E8, we find that their respective CMC values are large enough to observe a significant effect of the energy barrier on the overall rate of surfactant adsorption. In other words, for C12E8 and C10E8, the rate-limiting adsorption kinetics mechanism shifts from diffusion-controlled to mixed diffusion-barrier controlled as their premicellar surfactant bulk solution concentrations increase. We test the new methodology by predicting the short-time DST profiles at other initial surfactant bulk solution concentrations, and then comparing the predicted DST profiles with those measured experimentally. Very good agreement is obtained for the four C i E j nonionic surfactants considered. We also compare the results of implementing the new methodology with those of implementing the existing procedure, and conclude that using a model for the equilibrium adsorption isotherm can lead not only to different values of D and β, but it can also lead to a completely different determination of the rate-limiting adsorption kinetics mechanism. Since the new methodology proposed here does not require using a model for the equilibrium adsorption isotherm, we conclude that it should provide a more reliable determination of the rate-limiting adsorption kinetics mechanism, including the deduced kinetics parameters, D and β.A new methodology to obtain adsorption kinetics information solely from experimental dynamic surface tension data without using any equilibrium adsorption isotherm model.
Keywords: Nonionic surfactants; Adsorption kinetics; Diffusion-controlled; Mixed-controlled; Dynamic surface tension; Alkyl poly(ethylene oxide) nonionic surfactants;
Adsorption of mixtures of nonionic sugar-based surfactants with other surfactants at solid/liquid interfaces by Lei Zhang; P. Somasundaran (20-24).
Sugar-based surfactants can be synthesized from renewable materials and are environmentally benign. They have some unique solution and interfacial properties and have potential applications in a wide variety of processes, and there is a need for corresponding information on their behavior at various interfaces. In this study, co-adsorption of nonionic sugar-based n-dodecyl-β-d-maltoside (DM) and anionic sodium dodecyl sulfate (SDS) on alumina was studied as a function of mixing ratios and solution pHs. It is found that at solid–liquid interface, depending on the solid type and the solution conditions, there are various interactions that dictate synergy or antagonism. At pH 6 where alumina is positively charged, marked synergistic effects between DM and SDS were observed, while at pH 11 where alumina is negatively charged, SDS shows antagonistic adsorption effects with DM. The ratios of surfactant components on solids change as a function of surfactant structure and concentrations as well, indicating various interactions at solid/liquid interface under different conditions that can be utilized for many industrial processes.
Keywords: Adsorption; Surfactant mixtures; Sugar-based surfactants; n-Dodecyl-β-d-maltoside; Solid/liquid interface;
Adsorption of mixtures of nonionic sugar-based surfactants with other surfactants at solid/liquid interfaces by Lei Zhang; Rui Zhang; P. Somasundaran (25-31).
Synergy and antagonism between sugar-based surfactants, a group of environmentally benign surfactants, and cationic surfactants and nonionic ethoxylated surfactants have been investigated in this study with solids which adsorbs only one or other when presented alone. Sugar-based n-dodecyl-β-d-maltoside (DM) does not adsorb on silica by itself. However, in mixtures with cationic dodecyltrimethylammonium bromide (DTAB) and nonionic nonylphenol ethoxylated decyl ether (NP-10), DM adsorbs on silica through hydrophobic interactions. In contrast, although DM does adsorb on alumina, the presence of NP-10 reduces the adsorption of DM as well as that of the total surfactant adsorption. Such synergistic/antagonistic effects of sugar-based n-dodecyl-β-d-maltoside (DM) in mixtures with other surfactants at solid/liquid interfaces were systematically investigated and some general rules on synergy/antagonism in mixed surfactant systems are identified. These results have implications for designing surfactant combinations for controlled adsorption or prevention of adsorption.
Keywords: Adsorption; Surfactant mixtures; Sugar-based surfactants; n-Dodecyl-β-d-maltoside; Solid/liquid interfaces;
Interfacial and foaming properties of sulfydryl-modified bovine β-lactoglobulin by Thomas Croguennec; Anne Renault; Saïd Bouhallab; Stéphane Pezennec (32-39).
The effects of a control blocking of free cystein by N-ethylmaleimide on the interfacial behavior (kinetics of adsorption at the air/water interface, rheology of the interfacial layer) as well as on the foaming properties (density, stability) of β-lactoglobulin were investigated. Compared to native β-lactoglobulin (unmodified β-lactoglobulin), sulfydryl-modified β-lactoglobulin exhibited higher surface hydrophobicity, adsorbed faster at the air/water interface, had the capability to develop rapidly an interfacial layer with high shear elastic constant but exhibited a considerably lower shear elastic constant plateau value. Moreover, sulfydryl-modified β-lactoglobulin exhibited better foaming properties especially regarding the short-term foam stability suggesting that the initial rheology of the interfacial film is at least as much important for the general mechanism of foam stabilization as the potential viscoelasticity the interfacial film could reach on aging.The kinetic of protein adsorption and the initial viscoelasticity of the interfacial film is more important than the viscoelasticity the interfacial film can reached on aging for explaining the stability of native and sulfydryl-modified β-lactoglobulin foams.
Keywords: β-Lactoglobulin; Protein conformation; Adsorption; Surface load; Surface pressure; Interfacial rheology; Foaming properties;
Dynamic surface tension of micellar solutions in the millisecond and submillisecond time range by V.B. Fainerman; V.D. Mys; A.V. Makievski; J.T. Petkov; R. Miller (40-46).
The analysis of the available bubble life times and dead times for the bubble pressure tensiometer BPA-1S shows that dynamic surface tensions can be measured also for surfactant solutions at concentrations many times higher than the corresponding CMC. For the three nonionic surfactants Triton X-100, Triton X-45, and C14EO8 experiments are performed for solutions with a concentration of up to 200 times the CMC (C14EO8). Comparison of the experimental data with micelle kinetics models yields rate constants for the fast micelle dissolution process, which are in a good agreement with values obtained by other experimental methodologies.Bubble pressure tensiometry can be applied to surfactant solutions far above CMC. Experimental data for Tritons and C14EO8 yield micellar kinetics rate constants for the fast micelle dissolution process.
Keywords: Maximum bubble pressure tensiometer; Dynamic surface tension; Micellar surfactant solutions; Nonionic surfactants; Adsorption kinetics processes; Micelle dissolution process;
Adsorption of aqueous alkylphenol ethoxylate surfactants by mesoporous carbon CMK-3 by Guangming Liu; Shourong Zheng; Daqiang Yin; Zhaoyi Xu; Jie Fan; Fang Jiang (47-53).
Mesoporous carbon, CMK-3, was prepared using hexagonal SBA-15 mesoporous silica as the template and the adsorption of nonylphenol ethoxylates (NPE) onto CMK-3 was investigated. The adsorption process was well described using pseudo-second-order kinetics. At initial NPE concentrations of 107 and 530 mg l−1, the adsorption rate constants were found to be 5.6 × 10 −3 and 8.7 × 10 −4 g mg −1 min −1 , indicating that a higher initial concentration or adsorption amount resulted in a lower adsorption rate. NPE adsorption onto CMK-3 fitted a Langmuir–Freundlich model and the maximum amounts of NPE absorbed at 15, 25, and 35 °C were 923, 720, and 463 mg g−1, suggesting an elevated adsorption capacity of CMK-3 for NPE with decreased adsorption temperature. In addition, increasing adsorption temperature led to the change of the adsorption model from the Langmuir–Freundlich to the Langmuir model. N2 adsorption results showed that the adsorption of NPE led to a decrease in the mesopore volume of CMK-3. However, the pore width of NPE-loaded CMK-3 was found to be identical to that of CMK-3.Mesoporous carbon CMK-3 with ordered mesoporous structure and narrow pore size distribution was used to adsorb aqueous NPE.
Keywords: Mesoporous carbon CMK-3; Characterization; Nonylphenol ethoxylates; Adsorption;
Electrosorption capacitance of nanostructured carbon-based materials by Chia-Hung Hou; Chengdu Liang; Sotira Yiacoumi; Sheng Dai; Costas Tsouris (54-61).
The fundamental mechanism of electrosorption of ions developing a double layer inside nanopores was studied via a combination of experimental and theoretical studies. A novel graphitized-carbon monolithic material has proven to be a good electrical double-layer capacitor that can be applied in the separation of ions from aqueous solutions. An extended electrical double-layer model indicated that the pore size distribution plays a key role in determining the double-layer capacitance in an electrosorption process. Because of the occurrence of double-layer overlapping in narrow pores, mesopores and micropores make significantly different contributions to the double-layer capacitance. Mesopores show good electrochemical accessibility. Micropores present a slow mass transfer of ions and a considerable loss of double-layer capacitance, associated with a shallow potential distribution inside pores. The formation of the diffuse layer inside the micropores determines the magnitude of the double-layer capacitance at low electrolyte concentrations and at conditions close to the point of zero charge of the material. The effect of the double-layer overlapping on the electrosorption capacitance can be reduced by increasing the pore size, electrolyte concentration, and applied potential. The results are relevant to water deionization.The electrical double layer determines ion sorption and transport in nanostructured carbon-based materials; therefore, the material surface charge and pore size distribution play a key role in the electrosorption process.
Keywords: Electrosorption capacitance; Electrical double layer; Deionization; Nanostructured carbon;
Surface speciation of As(III) and As(V) in relation to charge distribution by Monika Stachowicz; Tjisse Hiemstra; Willem H. van Riemsdijk (62-75).
The adsorption of As(III) and As(V) on goethite has been studied as a function of pH and loading. The data can be successfully described with the charge distribution (CD) model (extended Stern layer option) using realistic species observed by EXAFS. The CD values have been derived theoretically. Therefore, the Brown bond valence approach has been applied to MO/DFT optimized geometries of a series of hydrated complexes of As(III) and As(V) with Fe(III) (hydr)oxide. The calculated ionic CD values have been corrected for the effect of dipole orientation of interfacial water, resulting in overall interfacial CD coefficients that can be used to describe the surface speciation as a function of pH and loading. For As(III), the main surface species is a bidentate complex and a minor contribution of a monodentate species is found, which is in agreement with EXAFS. The CD values have also been fitted. Such an analysis of the adsorption data resulted in the same surface species. The fitted CD values for the bidentate complex points to the presence of strong As―O bonds with the surface and a weaker As―OH bond with the free OH ligand. This agrees quantitatively with the MO/DFT optimized geometry. Interpretation of free fitted CD values for As(V) binding suggests that the main surface species is a non-protonated bidentate complex (B) with a contribution of a singly protonated surface complex (MH) at sub-neutral pH and high loading. In addition, a protonated bidentate surface complex (BH) may be present. The same species are found if the theoretical CD values are used in the data analysis. The pH dependency of surface speciation is strongly influenced by the charge attribution of adsorbed species to the electrostatic surface plane while the effect of loading is primarily controlled by the amount of charge attributed to the 1-plane, illustrating the different action of the CD value. The MO/DFT geometry optimizations furthermore suggest that for As(V) the B, MH and BH surface complexes may have very similar As―Fe distances which may complicate the interpretation of EXAFS data.The dipole corrected CD values, derived from MO/DFT optimized geometries of As(III) and As(V) complexes, are used to describe the adsorption of As(III) and As(V) on goethite.
Keywords: Iron oxide; HFO; Goethite; Hematite; Arsenic; Arsenate; Arsenite; MUSIC model; CD model; EXAFS; ATR-FTIR; Inner sphere; Outer sphere; Complexation;
A novel and simple method for finding the heterogeneity of adsorbents on the basis of adsorption kinetic data by Saeid Azizian (76-81).
The heterogeneity of adsorbent was characterized by a novel and simple method that uses adsorption kinetic data from solution. On the basis of different simulated adsorption kinetic data for heterogeneous adsorbents with two different adsorption sites, it was found that there is a deviation from linearity in pseudo-second-order adsorption kinetic models. The patterns of obtained diagrams ( t / q t vs t) shows five main classes of adsorption. On the basis of this novel and simple method it is possible to show that the surface of adsorbents is homogeneous or heterogeneous, and in the case of heterogeneous surfaces it is possible to find the differences between adsorption sites. For finding kinetic constants of adsorption on heterogeneous surfaces with two different sites, a new equation was presented and called the two-site pseudo-second-order (TS-PSO) model. Finally, some experimental kinetic data of adsorption were analyzed by the new method.
Keywords: Adsorption kinetic; Pseudo-second-order; TS-PSO; Surface heterogeneity; Kinetic modeling;
Adsolubilization of 2-naphthol into adsorbed layers of triblock PEO–PPO–PEO copolymers on hydrophobic silica particles by Daisuke Tsurumi; Kenichi Sakai; Tomokazu Yoshimura; Kunio Esumi (82-86).
Adsolubilization of 2-naphthol into an adsorbed layer of triblock poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO, Pluronics) copolymers on hydrophobically modified silica particles has been investigated. Four kinds of Pluronics (P103, P105, P123, and F108) were employed in order to understand the effect of the hydrophobicity of the surfactants on the adsolubilization. The amount of the Pluronics adsorbed of the maximum/saturation adsorption level was increased with a decrease in the HLB value, suggesting that the more hydrophobic Pluronics (P103 and P123) adsorb preferentially onto the hydrophobic silica surface over the more hydrophilic Pluronics (P105 and F108). The greater adsorbed amount of the more hydrophobic surfactants resulted in a greater amount of 2-naphthol adsolubilized into the adsorbed Pluronics layers. In the case of simultaneous addition of the Pluronics and 2-naphthol, the amount adsolubilized into the adsorbed P123 and P103 layers increased in their low-surfactant-concentration regime, reached a maximum, and then decreased with a further increase in the Pluronics concentration. On the other hand, for both the P105 and F108 copolymers, a decrease in the adsolubilized amount was not observed over the whole range of copolymer concentration investigated. This difference is attributed to a difference in the hydrophobicity of the micellar aggregates in solution and of the adsorbed layers on the hydrophobic surface. When 2-naphthol was added after replacement of the Pluronics supernatant by a surfactant-free solution, the final decrease in the adsolubilization was insignificant for all the Pluronics. Indeed, the maximum amount of adsolubilization was comparable to the corresponding amount obtained in the case of simultaneous addition.Adsolubilization of 2-naphthol into an adsorbed layer of Pluronics on hydrophobically modified silica particles has been investigated. Four kinds of Pluronics (Pluronic P103, P105, P123, and F108) were used.
Keywords: Adsolubilization; Pluronics; 2-Naphthol; HLB;
Micrometer-sized rodlike structure formed by the secondary assembly of cyclodextrin nanotube by Aihua Wu; Xinghai Shen; Yongke He (87-94).
In this work, we report the observation on the self-assembly of β-CD nanotube induced by 2-phenyl-5-(4-diphenylyl)1,3,4-oxadiazole (PBD) molecule with fluorescence microscopy and transmission electron microscopy (TEM). Micrometer-sized rodlike structure is formed by the secondary assembly of cyclodextrin nanotube driven by the inter-nanotubular hydrogen bonding. The effects of pH value, urea, DMF and NaCl on the formation of the rodlike structure are investigated. Dynamic light scattering (DLS) is applied to further characterize the formation of the PBD–β-CD nanotube. The effect of light scattering on the measurement of fluorescence anisotropy of PBD in the aqueous solutions of β-CD is corrected. A new mechanism of cyclodextrin aggregation is proposed for this system.Description: High-resolution TEM micrograph of the micrometer-sized rodlike structure formed by the secondary assembly of PBD–β-CD nanotubes. [ PBD ] = 1 × 10 −5 M , [ β - CD ] = 10 mM .
Keywords: Cyclodextrin nanotube; Secondary assembly; Hydrogen bonding; Transmission electron microscopy (TEM); Dynamic light scattering (DLS); Micrometer-sized rod;
Amphiphilic laminin peptides at air/water interface—Effect of single amino acid mutations on surface properties by Muthuselvi Lakshmanan; Aruna Dhathathreyan (95-102).
Amphiphilic derivative of the laminin peptide YIGSR and three other mutated peptides with mutation at Y with V (valine), I (isoleucine), and L (leucine) have been synthesized. The monolayer formation and the stability of these peptide analogues at air/water interface and the interaction with phospholipid monolayers have been studied using surface pressure–molecular area (π–A) and surface potential–molecular area (ΔV–A) isotherms. The single amino acid mutation in the native sequence leads to appreciable changes in surface activity, orientation and insertion into lipid monolayers with LIGSR showing most hydrophobic character while YIGSR showed most polar nature. The morphology of spread monolayers in the most close packed state was carried out using Brewster angle microscopy (BAM). LB films of these amphiphilic peptide derivatives transferred to hydrophilic quartz surfaces and hydrophobically modified surfaces showed significant changes in the work of adhesion as well as spreading behavior of water with the L substituted sequence showing maximum work of adhesion and the native sequence YIGSR, the least work of adhesion. From theoretical estimates, the long-range effects of the different amino acid residues in position 1 on the alkyl chains have been studied from charge on the carbon and hydrogen atoms of the alkyl tails. The present study demonstrates that amphiphilic derivatives of the laminin peptide YIGSR show enhanced activity compared to the original sequence. This work shows that the amino acid substituents on the head group clearly influence the distal methylene groups of the tail. Thus, any mutation of even single amino acid in a peptide sequence influences and plays an important role in determining macroscopic properties such as surface energy and adhesion both at air/solution and solid/solution interfaces.Single amino acid mutations in the amphiphilic analogues of laminin peptide YIGSR show large changes in the surface activity, and adhesion to model lipids.
Keywords: Amphiphilic analogues; Laminin peptides; Adhesion; Single mutation;
Electrohydrodynamic atomization for biodegradable polymeric particle production by Jingwei Xie; Liang Kuang Lim; Yiyong Phua; Jinsong Hua; Chi-Hwa Wang (103-112).
Electrohydrodynamic atomization (EHDA) has many applications such as electrospray ionization in mass spectroscopy, electrospray deposition of thin films, pharmaceutical productions, and polymeric particle fabrications for drug encapsulation. In the present study, EHDA was employed to produce biodegradable polymeric micro- and nanoparticles. The effects of processing parameters such as polymer concentration, flow rate, surfactants, organic salt, and setup configurations on the size and morphology of polymeric particles were investigated systematically. By changing the various processing parameters, controllable particle shape and size can be achieved. PLGA nanoparticles with size of around 250 nm can be obtained by using organic salts to increase the conductivity of the spraying solution even at a relatively high flow rate. A higher flow rate has the advantage of producing a stable cone spray and can be easily reproduced. Solid and porous particles can be fabricated using different experimental setups to control the organic solvent evaporation rate. Also, paclitaxel, a model antineoplastic drug, was encapsulated in polymeric particles which can be employed for controlled release applications. In short, EHDA is a promising technique to fabricate polymeric micro- or nanoparticles which can be used in drug delivery systems.Controllable size and morphology of biodegradable polymeric particles were achieved by the electrohydrodynamic atomization technique. Cenosphere and spherical particles were obtained by controlling the solvent evaporation rate under different experimental setups.
Keywords: Electrohydrodynamic atomization; Biodegradable; Polymeric; Nanoparticles; Microparticles;
Controllable size, shape and morphology of molybdic acid self-aggregated with rhodamine B to construct functional material by Zi Sheng Guan; Yu Zhang; Qiang Zhang; Dong Xu Li (113-122).
Controllable size, shape and morphology of rhodamine B/molybdic acid (RBMA) aggregates were prepared from a self-aggregation reaction in a molybdic acid and rhodamine B (RhB) coexisting solution. Nanodisks, as well as microcrystal rods and polyhexagonal microcrystal rods, have been obtained in conventional bulk solutions at different temperatures. Large-sized network microcrystal rods and branched fractal aggregates constructed with nanosubunits after the nucleation duration of an ice-water-cooled process have also been achieved under the evaporation-enhanced conditions on glass substrates. The factors affecting the size, shape and morphology of RBMA aggregates including temperature, nucleation and growth, and processing conditions are discussed. The results show that photofunctional molecules (RhB) modified the surface of the molybdic acid particles and influenced their self-aggregation. The temperature and nucleation play key roles in the formation of RBMA aggregates. The structures of RBMA aggregates were characterized by X-ray diffraction, infrared spectra and elemental dispersive spectroscopy. The results indicate that the aggregates show the characteristics of RhB-mediated hydrated ammonium molybdenum bronze with the metastable hexagonal phase. Visible-light-induced electrons transfer reactions in the RBMA aggregates from rhodamine B molecules to MoO3 matrixes were measured by UV–vis spectra and X-ray photoelectron spectra, and the fluorescent image was observed by laser scanning confocal microscopy.Nanoparticles, disks, hexagonal micro-crystal rods, network microcrystal rods and fractal branched aggregates were obtained from a self-aggregation reaction of molybdic acid particles with rhodamine B molecules under different conditions.
Keywords: Rhodamine B–molybdic acid aggregates; Self-aggregation; Bulk solution; Evaporation-enhanced conditions;
Hybrids of colloidal silica and waterborne polyurethane by Chien-Hsin Yang; Feng-Jiin Liu; Yun-Peng Liu; Wei-Tung Liao (123-132).
Waterborne polyurethane (WPU) was synthesized and followed by adding colloidal silica to prepare WPU–silica hybrids. The silica content in the hybrid thin films was varied from 0 to 50 wt%. The experimental results revealed that the viscosity of these hybrid solutions increased with increasing silica content and resulted in the aggregation of silica particle in the hybrid films. The latter result was evidenced by SEM examination. The effect of interaction between silica particle and urethane polymer chains is more significant with increasing silica content. The prepared hybrid films show much better thermal stability and mechanical properties than pure WPU. The optical transparence did not linearly decrease with increasing the silica fraction in the hybrid thin film. At below 20% silica content, the film transparence decreased with increasing silica content; the converse is true at above 20% silica content. These results showed that the prepared hybrid films demonstrated tunable transparence with the silica fraction in the films.Transmittance variation of the hybrid films (ca. 0.5 mm thickness) with different silica content over a wavelength range of 200–1100 nm. As shown in the inset, the transmittance at 633 nm decreases from 92% of pure WPU to 20% of the hybrid with 20% silica content, and then gradually increases from 20 to 87% of the hybrid with 50% silica content.
Keywords: Waterborne polyurethane/silica hybrid; Microstructure; Optical transparence;
Preparation of colloidal CdSe and CdS/CdSe nanoparticles from sodium selenosulfate in aqueous polymers solutions by Alexandra E. Raevskaya; Alexander L. Stroyuk; Stephan Ya. Kuchmiy (133-141).
Cadmium selenide nanoparticles formation at the interaction between CdCl2 and Na2SeSO3 in aqueous solutions of sodium polyphosphate and gelatin has been studied. Structural and optical properties of CdSe nanoparticles have been characterized. It has been shown that the temperature and the ratio of reagents concentrations are the basic parameters, controlling the size of CdSe nanoparticles. Photocatalytic activity of CdS nanoparticles in Na2SeSO3 reduction has been found and investigated; structural and optical properties of binary CdS/CdSe nanoparticles have been characterized. This photoreaction, when carried out in the presence of CdCl2, results in the formation of composite CdS/CdSe nanoparticles. It has been shown that slow interaction of adsorbed selenosulfate with surface-trapped CdS conduction band electrons is the limiting stage of the photocatalytic reaction.Formation of CdSe nanoparticles from Na2SeSO3 in aqueous polymers solutions has been studied. Photocatalytic activity of CdS nanoparticles in Na2SeSO3 reduction has been found. This photoreaction, when carried out in the presence of CdCl2, results in the formation of composite CdS/CdSe nanoparticles.
Keywords: CdSe nanoparticles; CdS nanoparticles; Sodium selenosulfate; Photochemical synthesis;
Preparation of hollow capsule-stabilized gold nanoparticles through the encapsulation of the dendrimer by Hongying Wu; Zelin Liu; Xudong Wang; Baohui Zhao; Jian Zhang; Chenxi Li (142-148).
The narrow-dispersed dendrimer-encapsulated gold nanoparticles without agglomeration were prepared from the grafted-dendrimers on the surface of the silica microspheres, successively by complexation of the gold chloride anion with the nitrogen atom of the dendrimer and the reduction with sodium borohydride as reductant. The hollow capsule-stabilized gold nanoparticles were prepared through the encapsulation of dendrimer successively by LBL self-assembly process of polyelectrolytes with modified-silica as template and removal of the silica core by hydrofluoric acid. The size of gold nanoparticles was 2.3 ± 0.8 nm . The catalytic activity of the capsule-stabilized gold nanoparticles was investigated in the reduction reaction of 4-nitrophenol to 4-aminophenol with sodium borohydride as reductant.
Keywords: Gold; Dendrimer; Capsule; Polyelectrolyte; PAMAM; Layer-by-layer; Silica; Nanoparticles; Catalysis; Modification;
Destructive aggregation: Aggregation with collision-induced breakage by R. Dennis Vigil; Isaac Vermeersch; Rodney O. Fox (149-158).
Mean-field population balance equations are used to describe the evolution of particle size distributions in a wide variety of systems undergoing simultaneous aggregation and breakage. In this paper we develop a population balance that includes aggregation combined with collision-induced particle breakage for arbitrary fragment distribution functions, provided that this distribution function depends only on the total mass of the particles undergoing a collision. We then develop a specific distribution function for arbitrary two-body collisions by postulating that each collision produces a transition-state aggregate having the morphology of a linear polymer. The behavior of the resulting equation is then analyzed for the case in which the collision kernel is a constant, and partial analytical solutions are derived and compared to corresponding Monte-Carlo simulation results. The computer simulations are then used to validate a proposed scaling law for the steady-state particle size distribution. Lastly, the behavior of the aggregation with collision-induced-breakage population balance equation is compared and contrasted with the behavior of an analogous aggregation with linear-breakage population balance equation.
Keywords: Aggregation; Fragmentation; Collision-induced breakage; Population balance equations;
Pickering emulsions stabilized solely by layered double hydroxides particles: The effect of salt on emulsion formation and stability by Fei Yang; Shangying Liu; Jian Xu; Qiang Lan; Fang Wei; Dejun Sun (159-169).
The formation and stability of liquid paraffin-in-water emulsions stabilized solely by positively charged plate-like layered double hydroxides (LDHs) particles were described here. The effects of adding salt into LDHs dispersions on particle zeta potential, particle contact angle, particle adsorption at the oil–water interface and the structure strength of dispersions were studied. It was found that the zeta potential of particles gradually decreased with the increase of salt concentration, but the variation of contact angle with salt concentration was very small. The adsorption of particles at the oil–water interface occurred due to the reduction of particle zeta potential. The structural strength of LDHs dispersions was strengthened with the increase of salt and particle concentrations. The effects of particle concentration, salt concentration and oil phase volume fraction on the formation, stability and type of emulsions were investigated and discussed in relation to the adsorption of particles at the oil–water interface and the structural strength of LDHs dispersions. Finally, the possible stabilization mechanisms of emulsions were put forward: the decrease of particle zeta potential leads to particle adsorption at the oil–water interface and the formation of a network of particles at the interface, both of which are crucial for emulsion formation and stability; the structural strength of LDHs dispersions is responsible for emulsion stability, but is not necessary for emulsion formation.Appearance of the paraffin oil-in-water emulsions stabilized by LDHs particles 48 h after preparation. Black area: emulsion; O: oil; D: dispersion; W: clear water.
Keywords: Layered double hydroxides (LDHs); Particles; Salt; Dispersion; Adsorption; Structural strength; Emulsion; Formation and stability;
Formation mechanism of nanotubes comprising layers of PbS nanoparticles in polymer–surfactant solutions by Maria Orphanou; Epameinondas Leontidis; Tasoula Kyprianidou-Leodidou; Walter Caseri; Frank Krumeich; Kyriacos C. Kyriacou (170-177).
The crystallization of PbS in aqueous solutions containing the surfactant sodium dodecyl sulfate (SDS) and hydrophilic polymers resulted in a novel type of metastable nanotubes, the walls of which consist of layers of ordered PbS nanoparticles, apparently separated by layers of surfactant molecules. Information on the mechanism of formation of these structures was obtained by focusing on the roles of the polymer, and of the insoluble lead dodecyl sulfate (Pb(DS)2) present in the system. TEM investigations of the early stages of crystallization revealed the coexistence of PbS and Pb(DS)2 precipitates, the latter being surprisingly important for nanotube formation, and allowed to follow the evolution of layered structures from combination of the two types of crystals. Six different hydrophilic polymers have been used, which interact with SDS with varying strengths. Surprisingly, and in contrast to previous hypotheses, layered nanostructures were observed in all polymer solutions, regardless of the strength of polymer–surfactant interactions. This indicates that, although the presence of a polymer is necessary, polymer–SDS interactions are not a driving force for the formation of the layered structures and nanotubes. On the contrary, the interactions between the polymer chains and the growing particles appear to be of the utmost importance. Results presented here can be interpreted in terms of two alternative mechanisms for layered nanostructure and nanotube formation.
Keywords: PbS nanoparticles; Polymer–surfactant solutions; Layered structures; Nanotubes;
Dendron-protected Au nanoparticles—Effect of dendritic structure on chemical stability by Christine S. Love; Ian Ashworth; Colin Brennan; Victor Chechik; David K. Smith (178-186).
A series of gold nanoparticles stabilised by ‘Newkome-type’ dendritic branching has been synthesised and fully characterised. In particular, the properties and behaviour of these hybrid materials are compared with those of a previously reported set of nanoparticles stabilised by dendrons constructed using l-lysine building blocks. The rates of cyanide-induced nanoparticle decomposition were determined, and it was found that the rate of decomposition increased on the introduction of dendritic branching. Furthermore, ‘Newkome-type’ dendrons were significantly more effective at protecting the encapsulated gold nanoparticle than the l-lysine based dendrons. It is proposed that this observation can be explained on the basis of more effective packing and surface coverage by the ‘Newkome-type’ dendrons. Importantly, this study therefore demonstrates that the organic chemical structure of dendritic ligands plays a crucial role in controlling the reactivity of self-assembled hybrid nanostructures.In these hybrid nanomaterials, the chemical structure of the organic shell directly controls the chemical stability of the inorganic gold core.
Keywords: Dendrimers; Kinetics; Nanoparticles; Stability; Structure-activity relationships; UV–vis spectroscopy;
A generalized model for the stability of polymer colloids by Zichen Jia; Cornelius Gauer; Hua Wu; Massimo Morbidelli; Alba Chittofrati; Marco Apostolo (187-202).
A generalized model has been proposed to describe the stability of polymer colloids stabilized with ionic surfactants by accounting simultaneously for the interactions among three important physicochemical processes: colloidal interactions, surfactant adsorption equilibrium, and association equilibria of surface charge groups with counterions at the particle–liquid interface. A few Fuchs stability ratio values, determined experimentally for various salt types and concentrations through measurements of the doublet formation kinetics, are used to estimate the model parameters, such as the surfactant adsorption and counterion association parameters. With the estimated model parameters, the generalized model allows one to monitor the dynamics of surfactant partitioning between the particle surface and the disperse medium, to analyze the variation of surface charge density and potential as a function of the electrolyte type and concentration, and to predict the critical coagulant concentration for fast coagulation. Three fluorinated polymer colloids, stabilized by perfluoropolyether-based carboxylate surfactant, have been used to demonstrate the feasibility of the proposed colloidal stability model.Comparisons of the critical coagulant concentrations (ccc) for fast coagulation measured experimentally with those estimated by the model for three polymer latexes using H2SO4 and NH4HSO4 as electrolyte, respectively.
Keywords: Colloidal stability; Fuchs stability ratio; Surface charge; Surfactant adsorption; Counterion association; Hydration force;
Nitrate absorption through hydrotalcite reformation by Ray L. Frost; Anthony W. Musumeci (203-206).
Thermally activated hydrotalcite based upon a Zn/Al hydrotalcite with carbonate in the interlayer has been used to remove nitrate anions from an aqueous solution resulting in the reformation of a hydrotalcite with a mixture of nitrate and carbonate in the interlayer. X-ray diffraction of the reformed hydrotalcites with a d(003) spacing of 7.60 Å shows that the nitrate anion is removed within a 30 min period. Raman spectroscopy shows that two types of nitrate anions exist in the reformed hydrotalcite (a) nitrate bonded to the ‘brucite-like’ hydrotalcite surface and (b) aquated nitrate anion in the interlayer. Kinetically the nitrate is replaced by the carbonate anion over a 21 h period. Two types of carbonate anions are observed. This research shows that the reformation of a thermally activated hydrotalcite can be used to remove anions such as nitrate from aqueous systems.Thermally activated hydrotalcite based upon a Zn/Al hydrotalcite with carbonate in the interlayer has been used to remove nitrate anions from an aqueous solution resulting in the reformation of a hydrotalcite with a mixture of nitrate and carbonate in the interlayer.
Keywords: Hydrotalcite; Brucite; Pyroaurite; Takovite; Nitrate removal; Raman microscopy; Memory effect;
Chlorination of aromatic compounds in micellar media: Regioselectivity by B.S. Samant; Y.P. Saraf; S.S. Bhagwat (207-213).
Chlorination of phenol and ortho-chlorophenol was studied in micellar media in order to observe the effect on regioselectivity. Hydrogen peroxide/hydrochloric acid–aqueous system, which is environmentally a safer route was employed for chlorination. Selectivity ratio was found to be dependent on the nature and concentration of the surfactant. Ortho/para selectivity ratio up to 12 was realized for the chlorination of phenol. 2,6-/2,4-dichlorophenol ratio up to 1.01 was realized for the chlorination of ortho-chlorophenol.Chlorination of phenol and ortho-chlorophenol was studied in micellar media with an aim to alter the regioselectivity. Hydrogen peroxide/hydrochloric acid–aqueous system, which is environmentally a safer route was employed for chlorination.
Keywords: Phenol; Ortho-chlorophenol; Chlorination; Micellar catalysis; Regioselectivity;
Preparation, structure and thermal stability of onium- and amino-functionalized silicas for the use as catalysts supports by T. Kovalchuk; H. Sfihi; L. Kostenko; V. Zaitsev; J. Fraissard (214-229).
We explored and compared several synthetic methods of grafting silica with strong (alkyltriphenylphosphonium, tetralkylammonium, propylpyridinium and dialkylimidazolium) and weak (γ-aminopropyl, γ-(N-imidazolyl)propyl) anion-exchanging groups starting with commercially available chloroalkyl- and γ-aminopropylsilanes. Structure of the intermediate and final materials was investigated by elemental analysis, titration, 13C, 29Si, 31P MAS NMR, DRIFT, and TPD MS. The derivatives of alkyltriphenylphosphonium, propylpyridinium and dialkylimidazolium cation can be prepared with satisfactory quaternisation yields (ca. 30–100%) via the nucleophilic substitution of γ-chloropropyl groups either in the silane or in chloropropylsilica, resulting in bonded phases with moderate densities: 0.2–1.0 group nm−2 (onium salts) and 0.2–1.5 group nm−2 (amines). Parallel one-pot end-capping/hydrophobization can be done if a mixture of target silane with end-capping reagent or γ-chloropropylsilane is used. The grafted layer is highly stable at the level of Si–C bonds and decomposes at ca. 400 °C, while the onium functions begin to decompose at ca. 250 °C, lowering the thermal stability of materials. Thus, anion-exchanging silicas can be envisaged for the use as catalyst supports at moderate temperatures.
Keywords: Functionalization; Grafting; Silica; End-capping; Ion-exchanger; 13C NMR; 29Si NMR; 31P NMR; DRIFT;
Chemical discrimination by a kinetic model of organic photooxidation in a heterosupramolecular assembly by Gregory J. Wilson; Geoffrey D. Will (230-239).
The photooxidation of range of common organic pollutants in a dye-sensitised photoelectrochemical cell (DS-PEC) is reported. A photoanode was prepared by the chemisorption of a photosensitiser, cis-bis-( 2 , 2 ′ -bipyridine)-( 4 , 4 ′ -bis-(methyl)phosphonato- 2 , 2 ′ -bipyridine)ruthenium(II) dichloride ([Ru(bpy)2(dmpbpy]2+), to a nanoporous nanocrystalline TiO2 thin film on a conducting glass substrate. The photoanode was coupled to a platinum electroplated fluorine doped tin oxide glass substrate in a two electrode assembly and the cell cavity was filled with an aqueous solution of organic pollutants and irradiated with λ > 420 nm to give a measurable photocurrent. In addition to the ability of this cell to photooxidise a range of chemically diverse organic pollutants, the application of a kinetic model to observed photocurrent transients allowed the study of interfacial electron transfer processes. Through the mathematical fit of a five-parameter double exponential decay function, evidence to support numerous interfacial reactions for the oxidation process were identified. Rapid oxidation of species in close proximity to the photooxidation centre was proposed as the kinetically fast interfacial process with a first-order rate constant of the order 0.4 s−1. The slower process was attributed to the diffusion of oxidisable species from the solution bulk to the surface prior to oxidation with a first-order rate constant of the order 0.01 s−1. Theoretical profiling of the kinetic events supported the biphasic assignment of interfacial processes and indicated that non-exhaustive oxidation occurs for the solution concentrations examined.
Keywords: Photocatalysis; Dye-sensitised; Organic-pollutant; Photooxidation; Degradation; Visible-light;
Structural characterization of Am incorporated into calcite: A TRLFS and EXAFS study by T. Stumpf; M. Marques Fernandes; C. Walther; K. Dardenne; Th. Fanghänel (240-245).
Calcite homogeneously doped with Am(III) and Cm(III) was synthesized in a mixed-flow reactor. The mechanism of incorporation of these actinides (An) into calcite was investigated by time-resolved laser fluorescence spectroscopy. Two different An(III)/calcite species were found. One has been identified as ions bonded onto the calcite surface. The second An(III) species has lost its complete hydration sphere and is incorporated into the calcite bulk structure. Both Cm(III)/calcite and Am(III)/calcite complexes have been characterized by their fluorescence emission spectra and lifetimes. Structural parameters of the incorporated Am(III) species determined by EXAFS indicate a coordination number of 6.3 ± 0.6 and distances of 2.40 ± 0.01 Å for the first Am―O shell.
Keywords: Americium; Curium; Calcite; Surface complexation; Solid solutions; Time-resolved laser fluorescence spectroscopy (TRLFS); Extended X-ray absorption fine structure (EXAFS);
Controlled production of ZnO nanoparticles from zinc glycerolate in a sol–gel silica matrix by Rodoula Moleski; Epameinondas Leontidis; Frank Krumeich (246-253).
The controlled production of ZnO nanoparticles within an amorphous silica matrix is achieved using a new methodology consisting of four stages. First, precursor zinc glycerolate nanoparticles are produced within reversed micelles of glycerol in heptane stabilized by the surfactant Aerosol-OT (bis-ethylhexyl sodium sulfosuccinate, AOT). The surface of these nanoparticles is then modified by exchanging AOT with bis-trimethoxysilyl-ethane (BTME). The surface-modified nanoparticles are copolymerized with tetramethoxysilane (TMOS) to provide a composite silica material, in which the nanoparticles are apparently dissolved, producing a uniform distribution of zinc in the silica matrix. Finally, the conversion of zinc to ZnO is achieved by heating the material at 700 °C, leading to a uniform dispersion of very small ( < 10 nm ) ZnO particles within the amorphous matrix. The fluorescence spectrum of the ZnO particles within the matrix is blue-shifted, as expected from the strong quantum confinement achieved. The properties of the system at all stages in this synthetic process are monitored using TEM, XRD, fluorescence and FT-IR spectroscopy. Glycerol forms complexes with many metal ions, so the present procedure may be generalized to provide uniform distributions of metal ions and subsequently metal oxide nanoparticles in amorphous silica.
Keywords: ZnO nanoparticles; Zinc glycerolate; W/O microemulsions; Silica-based composite material;
Reactivity of ionic liquids with kaolinite: Melt intersalation of ethyl pyridinium chloride in an urea-kaolinite pre-intercalate by Sadok Letaief; Tamer A. Elbokl; Christian Detellier (254-258).
This paper reports a new route for the intercalation of an ionic liquid, namely 1-ethyl pyridinium chloride, into the interlamellar spaces of kaolinite. The intercalation was achieved using a kaolinite-urea intercalate as a starting material. The results of the XRD, FTIR, and TGA analyses confirmed the intercalation of ethyl pyridinium in the interlamellar spaces of kaolinite. 13C CP/MAS spectra indicated the complete displacement of urea by ethyl pyridinium. 29Si and 27Al NMR spectra of the starting materials and the products are also discussed as well as the results of the elemental analysis of the produced nanohybrid material.A new route for the intercalation of an ionic liquid into the interlamellar spaces of kaolinite is described, using a kaolinite-urea intercalate as a starting material.
Keywords: Kaolinite; Nanohybrids; Intercalation; Molten salts; Ionic liquids; FTIR; TGA; X-ray diffraction; NMR;
J-aggregates in matrix stabilized two-dimensional azobenzene derivatives by B. Vijai Shankar; Archita Patnaik (259-266).
A two-component film technique at the air–water interface has been used for fabricating matrix stabilized azobenzene J-aggregates. Langmuir monolayers of (E)-1-(3-chloro-4-(alkyloxy)phenyl)-2-phenyldiazene (C n CD, n = 8 , 10 , 12 ) have been prepared with stearic acid (STA) as the two-dimensional matrix. Miscibility studies at a molecular level, explored from the monolayer pressure–area isotherms revealed a phase separation of the C n CD from the stearic acid matrix at a compression pressure of 10 mN/m. A 43-nm strong red shift in the 350 nm π – π ∗ absorption feature implied formation of highly ordered J-aggregates of C n CDs in conformity with atomic force microscopy and micro-Raman spectral characteristics. While a one-component C n CD failed to form a 2D monolayer, the STA supported C n CD binary system crossed a mixed monolayer phase followed by compression, leading to the formation of matrix stabilized C n CD J-aggregates.
Keywords: Mixed monolayer; LB films; Micro-Raman spectroscopy; J-aggregates;
Filtration application from recycled expanded polystyrene by C. Shin (267-271).
Water-in-oil emulsion with drop size less than 100 μm is difficult to separate. Coalescence filtration is economical and effective for separation of secondary dispersions. Coalescence performance depends on flow rate, bed depth, fiber surface properties, and drop size. The amount of surface area of the fibers directly affects the efficiency. A new recycling method was investigated in the previous work in which polystyrene (PS) sub-μm fibers were electro-spun from recycled expanded polystyrene (EPS). These fibers are mixed with micro glass fibers to modify the glass fiber filter media. The filter media are tested in the separation of water droplets from an emulsion of water droplets in oil. The experimental results in this work show that adding nanofibers to conventional micron sized fibrous filter media improves the separation efficiency of the filter media but also increases the pressure drop. An optimum in the performance occurs (significant increase in efficiency with minimal increase in pressure drop) with the addition of about 4% by mass of 500 nm diameter PS nanofibers to glass fibers for the filters.Coalescence filtration is economical and effective for separation of secondary dispersions. A new recycling method was investigated in the work in which polystyrene (PS) sub-μm fibers were electro-spun from recycled expanded polystyrene (EPS). SEM photograph of nanofiber mixed with glass fiber in filter samples.
Keywords: Filtration; Nanofiber; Electrospinning; Coalescence; Recycle;
Surface phase behavior of di-n-tetradecyl hydrogen phosphate in Langmuir monolayers at the air–water interface by Md. Mufazzal Hossain; Ken-ichi Iimura; Teiji Kato (272-277).
Surface phase behavior of di-n-tetradecyl hydrogen phosphate, DTP, has been studied by measuring π – A isotherms with a film balance and observing monolayer morphology with a Brewster angle microscopy (BAM) at different temperatures. A generalized phase diagram, which shows a triple point for gas (G), liquid-expanded (LE) and liquid-condensed (LC) phases at about 32 °C, is constructed for the amphiphile. Below the triple point, a first-order G–LC phase transition has been shown to occur, whereas a first-order G–LE phase transition followed by another first-order LE–LC transition has been found to take place at a temperature above the triple point. The amphiphile shows the fingering LC domains with uniform brightness indicating the presence of untilted molecules. The domain shapes are independent of the change in temperature and compression rate. The existence of similar fingering domains over a wide range of temperature is rather uncommon in the monolayer systems and is considered to be due to the restricted movement of the molecules incorporating into the LC phase. Because the two-alkyl chains are directly attached to two covalent bonds of the phosphate head group, the rearrangement of the molecules, which is an essential condition for the circular domain formation, needs the movement of the whole molecules including the hydration sphere. The difficulty related to such a movement of the molecules causes fingering domains, which are independent of external variables.Shapes of the domains in the DTP monolayers at different temperatures and compression rates.
Keywords: Langmuir monolayers; Phase transition; Brewster angle microscopy; Di-n-tetradecyl hydrogen phosphate; Triple point;
Synthesis and pore formation study of amorphous mesoporous aluminophosphates in the presence of citric acid by Gang Liu; Mingjun Jia; Zhou Zhou; Lei Wang; Wenxiang Zhang; Dazhen Jiang (278-286).
Amorphous mesoporous aluminophosphates (AlPO) with high thermal stability were synthesized from Al(NO3)3 and H3PO4 in the presence of citric acid (CA). The effects of different synthetic conditions, such as pH value, citric acid content, and calcined temperature, on the formation of the mesoporous structure of AlPO materials were investigated. The results of N2 adsorption/desorption and other characterization means demonstrate that the presence of a certain amount of citric acid in the synthetic mixture can result in the formation of uniform mesoporous AlPO materials in a wide pH range from 3.5 to 10. Thermal gravimetry and differential thermal analysis suggest that the existence of a moderate interaction between citric acid and the AlPO network might be a critical factor in obtaining uniform mesostructure. Therefore, as an organic additive, citric acid can be regarded as a template for the mesopore formation of AlPO materials.
Keywords: Mesopores; Aluminophosphates; Thermal stability; Citric acid; Templates; Organic additives;
Morphology and water barrier properties of organosilane films: The effect of curing temperature by Guirong Pan; Dale W. Schaefer; Jan Ilavsky (287-293).
The morphology of silane films and the response of these films to water vapor are studied by neutron reflectivity, X-ray reflectivity, ellipsometry, and contact angle. The systems studied include bis-[3-(triethoxysilyl)propyl]tetrasulfide (bis-sulfur) and bis-[trimethoxysilylpropyl]amine (bis-amino), as well as mixtures of these two silanes. The effect of curing temperature on water-barrier properties is determined by comparing data for films cured at 180 °C with existing data for films cured at 80 °C. Higher curing temperature leads to an increase of the crosslink density as well as chemical modification for the sulfur-containing films. For bis-amino silane films, on the other hand, the effect on the water-barrier ability is negligible. Bis-amino silane is fully hydrolyzed and condensed at the curing temperature of 80 °C, so further increasing cure temperature does not affect the bulk structure of the film. For bis-sulfur and mixed films, however, higher curing temperature accelerates the hydrolysis and condensation, leading to denser films with better water-barrier performance.Higher curing temperature leads to an increase of the crosslink density as well as chemical modification of the sulfur-containing silane films. For bis-amino silane films, on the other hand, the effect of cure temperature on the water barrier ability is negligible. Bis-amino silane is fully hydrolyzed and condensed at a curing temperature of 80 °C, while a higher curing temperature is needed for sulfur-containing films.
Keywords: Silane films; Neutron reflectivity; Swelling; Interface; Processing variable;
Drop formation via breakup of a liquid bridge in an AC electric field by Beom Seok Lee; Hye-Jung Cho; Jeong-Gun Lee; Nam Huh; Jeong-Woo Choi; In Seok Kang (294-307).
Experimental results are presented for the study of drop formation mechanism in a newly proposed electrohydrodynamic (EHD) method of drop generation in an AC electric field. In the method, a small drop is generated in two stages. A pendant drop is elongated with large oscillation by an electric force in the first stage. Then, it undergoes formation and breakup of a liquid bridge between the upper nozzle and the insulator-coated lower flat plate in the second stage. It is found that there exists a resonant frequency for maximum oscillation, which leads to an efficient drop formation in the latter stage. It is also found that breakup of liquid bridge is accelerated by the electrowetting tension acting on the drop perimeter contacting the insulator-coated flat plate. Thus the whole procedure of drop formation depends heavily on the frequency of AC field and the properties of the insulator such as hydrophilicity, thickness, and the dielectric constant. It is demonstrated that a wide range of drop size, from picoliter to nanoliter, can be obtained by controlling such key parameters without changing the nozzle diameter.Mechanism in a newly proposed EHD method of drop formation in an AC electric field is studied and it is divided into two stages, such as drop elongation and breakup of a liquid bridge.
Keywords: EHD method; AC electric field; Liquid bridge; Electrowetting; Resonant frequency; Insulator;
Micrometrically scaled textured metallic hydrophobic interfaces validate the Cassie–Baxter wetting hypothesis by Edward Bormashenko; Yelena Bormashenko; Gene Whyman; Roman Pogreb; Oleg Stanevsky (308-311).
The possibility of forming a hydrophobic metallic interface is shown when it is micrometrically textured. On such surface obtained by gold coating the polymer honeycomb template, the apparent contact angle of water was observed to be close to or greater than 90°. The metal hydrophobicity is explained by trapping air inside pores of pattern according to the Cassie–Baxter wetting model. The agreement between calculated and observed values of the apparent contact angle justifies the applicability of this model in the present case. Formation of the acute local (Young) angle on the pore surface is provided by its concave form.
Keywords: Wetting of metals; Polymer pattern; Textured surfaces; Cassie–Baxter model;
Correlation between surface tension, density, and sound velocity of liquid metals by Sidney Blairs (312-314).
The inter-relationship of surface tension σ, density ρ, and sound velocity c has been examined for forty-one liquid metals. Sound velocities correlate with the equation, log c = 0.5526 log ( σ / ρ ) + 5.4364 . Unknown sound velocities may be estimated using surface tension and liquid density values.
Keywords: Sound velocities; Surface tension; Density; Liquid metals;
Clouding phenomenon and SANS studies on tetra-n-butylammonium dodecylsulfate micellar solutions in the absence and presence of salts by Kabir-ud-Din; Deepti Sharma; Ziya Ahmad Khan; V.K. Aswal; Sanjeev Kumar (315-321).
Clouding phenomenon in aqueous micellar solutions of an anionic surfactant tetra-n-butylammonium dodecylsulfate (TBADS) has been observed as a function of surfactant concentration. Small-angle neutron scattering (SANS) experiments in these systems show clustering of micelles as the temperature approaches the cloud point (CP). The individual micelles and the clusters of micelles coexist at CP. The clustering of micelles depends on the surfactant concentration and temperature. It is proposed that clustering is due to depletion of H-bonded water present around the butyl chains at the micellar surface. This is associated with entropy gain which is considered to be the major thermodynamic factor related to micellar aggregation. The structures (clusters) that emerge depend on the relative lengths of the alkyl chains of the counterion and can be tuned by the temperature.
Keywords: Cloud point (CP); Tetra-n-butylammonium dodecylsulfate (TBADS); Quaternary salts; Small-angle neutron scattering (SANS); Dynamic light scattering (DLS);
A novel dispersion method comprising a nucleating agent solubilized in a microemulsion, in polymeric matrix by D. Libster; A. Aserin; N. Garti (322-329).
This second part of our paper focuses on structural characterization of the microemulsion for increasing the crystallization rate of polypropylene (PP) through the entrapment of nucleating agent (nucleator) HPN-68, serving as a transport vehicle. Our concept is based on creating an advantage in dispersion capability of the nucleator that is dissolved in a nanoreactor vehicle, compared with its conventional loading as a crystalline powder. The advantage was achieved by solubilizing the HPN-68 in a microemulsion to decrease its size from micro- to nanoscale. The microemulsions were introduced to the target PP using a mixer. By the end of the mixing, when the water phase had evaporated, only the nucleator and the surfactant remained in the matrix. DSC results showed a 24% improvement in nucleation efficiency of PP by this novel method. It was shown that solubilization of the nucleator depends on the water activity in the microemulsion, and the presence of the nucleator opposes formation of the W/O phase. Light scattering, SD-NMR, and SAXS results showed that HPN-68 is accommodated in the water phase and at the interface, and significantly reduces the level of order in the microemulsion. In intermediate water content, a worm-like structure was proposed instead of the classical bicontinuous one. The structure was confirmed by SAXS and SD-NMR analysis. Viscosity measurements revealed structural transitions in the microemulsions.This paper focuses on structural characterization of the microemulsion for increasing the crystallization rate of polypropylene through the entrapment of nucleating agent (nucleator) HPN-68, serving as a transport vehicle. It was shown that solubilization of the nucleator depends on the water activity in the microemulsion, and the presence of the nucleator opposes formation of the W/O phase.
Keywords: Microemulsion; Nucleating agent; Solubilization; Phase diagram; Dispersion; Crystallization; Polypropylene; Worm-like structure;
Charge number effect on the miscibility of inorganic salt and surfactant in adsorbed film and micelle: Inorganic salt–dodecylammonium chloride mixtures by Hidemi Iyota; Takako Tomimitsu; Makoto Aratono (330-334).
The effect of inorganic salts with different charge numbers of cations on the adsorption and micelle formation of dodecylammonium chloride (DAC) was clarified by applying the thermodynamic treatment of surfactant mixtures to mixtures of DAC with calcium and lanthanum chlorides and comparing the results with those of the sodium chloride–DAC mixture in the previous study. Surface tension of aqueous solutions of the salt–DAC mixture was measured as a function of the total molality of the mixture and the mole fraction of DAC in the mixture at 298.15 K under atmospheric pressure. Judging from the phase diagrams of adsorption and micelle formation obtained from the surface tension measurement, dodecylammonium cations expel inorganic cations from the adsorbed film and micelle and the repulsive interaction between dodecylammonium and inorganic cations increases with increasing charge number of the inorganic cation.The repulsive interaction between inorganic cations and dodecylammonium anions in adsorbed films and micelles increases with increasing charge number of the inorganic cations.
Keywords: Charge number of inorganic ion; Mixture of inorganic salt and dodecylammonium chloride; Surface tension of a mixture; Miscibility in adsorbed film and micelle; Phase diagrams of adsorption and micelle formation;
Interactions between nonionic Triton X surfactants and cholesterol-containing phosphatidylcholine liposomes by Chorng-Shyan Chern; Hsin-Cheng Chiu; Yu-Shiue Yang (335-340).
Solubilization kinetics experiments were developed to study the effects of the polyethylene glycol chain length of Triton X surfactants on their interactions with the cholesterol-containing phosphatidylcholine vesicles. An empirical liposome stability ratio was used to describe the vesicle solubilization process. The effectiveness of Triton X surfactants in solubilizing vesicles decreases with increasing polyethylene glycol chain length of surfactants. It was also shown that vesicles containing the intercalated surfactant molecules with the largest number of ethylene glycol units per molecule exhibited the exceedingly retarded solubilization behavior. Independent experiments based on a thermodynamic approach provide supporting evidence for the conclusions obtained from solubilization kinetics experiments.Solubilization kinetics experiments and an empirical liposome stability ratio were developed to study the effects of the polyethylene glycol chain length of Triton X surfactants on their interactions with liposomes.
Keywords: Liposome; Nonionic surfactants; Structural transformation of vesicles; Solubilization kinetics experiments; Liposome stability ratio;
Effects of dioctadecyl dimethyl ammonium chloride on the rheological behavior of behenyl trimethyl ammonium chloride/1-hexadecanol/water ternary system by Hidetaka Akatsuka; Yasuhiro Ohara; Yasufumi Otsubo (341-346).
The effects of dioctadecyl dimethyl ammonium chloride (DODAC) on the rheological properties of ternary systems consisting of behenyl trimethyl ammonium chloride (C22TAC), 1-hexadecanol (C16OH), and water are studied to improve the long-term stability and to establish the preparation method of cosmetic products. The basic ternary systems behave as solids at low stresses, due to the formation of lamella liquid crystals called α gel. The additions of DODAC to ternary systems cause the rupture of α gel structures and transformation to vesicles. The structures of molecular assemblies are confirmed through particle size distribution, differential scanning calorimetry, and freeze fracture electron microscopy. The vesicle structures formed in coexistence of single-chain surfactant and double-chain surfactant are highly stable. Because the quaternary systems are considered to be constructed by the mixtures of α gel and vesicles at the appropriate concentrations of DODAC, the rheology can be controlled by the structural balance between them.The additions of dioctadecyl dimethyl ammonium chloride to ternary systems cause the reduction of viscosity. The double step curves imply the existence of two different molecular assemblies.
Keywords: Double-chain surfactant; Lamella liquid crystal; Long-chain alcohol; Rheology; Vesicle;
Rheological properties and particle behaviors of a nondilute colloidal dispersion composed of ferromagnetic spherocylinder particles subjected to a simple shear flow: Analysis by means of mean-field approximation for the two typical external magnetic field directions by Tomonori Watanabe; Masayuki Aoshima; Akira Satoh (347-355).
We have analyzed the orientational distributions and rheological properties of a nondilute colloidal dispersion composed of ferromagnetic spherocylinder particles subjected to a simple shear flow. In order to understand the effects of the magnetic interactions between the particles, we have applied the mean-field theory to a nondilute colloidal dispersion for the two typical external magnetic field directions, that is, the direction parallel to the shear flow and the direction parallel to the angular velocity vector of the shear flow. The main results are summarized as follows. The particle–particle interactions suppress the Brownian motion of the particles and, therefore, make the particles incline toward the same direction. For the magnetic direction parallel to the shear flow, the influence of the particle–particle interactions makes the peak of the orientational distribution sharper and higher. The viscosity generally increases as the interactions between particles become stronger in the case where the effects of the shear flow and magnetic field are relatively small. For the magnetic direction parallel to the angular velocity vector of the shear flow, the influence of the particle–particle interactions on the orientational distribution appears significantly, when the influences of the shear flow and magnetic field are not so strong that the particles can be aligned sufficiently to form stable chainlike clusters in a certain direction.The mean-field approximation has been applied in order to understand the effects of the magnetic interactions between the rodlike particles under circumstances of a simple shear flow and an external magnetic field.
Keywords: Ferromagnetic colloidal dispersion; Aggregation phenomena; Simple shear flow; Spherocylinder; Orientational distribution function; Rheological properties;
Gushing in canned beer: The effect of ultrasonic vibration by Kisor K. Sahu; Yasuhiro Hazama; Keiichi N. Ishihara (356-362).
Everybody has had the experience of a canned carbonated drink overflowing and soiling their clothes. It is difficult to guess the amount of overflow before opening the can, although the phenomenon can be simply explained as the result of the formation of gas bubbles. In this article, we report the surprising result that intensive shaking using ultrasonic vibration can calm this effect in beer. These experiments showed evidence of a memory effect in liquid. The ‘calming down’ is due to a fine balancing act between a change in the amount of microbubbles (or embryos) and a change in the pattern of their size distribution. Our experimental evidence shows that modification of the pre-existing microbubbles noticeably influences the subsequent nucleation, and this may open a new route to nucleation studies.Demonstration of memory effect that has been initiated by ultrasonic vibration. The minimum spillover takes place despite high level of excitation by adjusting the first rest time.
Keywords: Homogeneous nucleation; Effervescence; Surface tension; Beer;
General solution to two-dimensional nonslipping JKR model with a pulling force in an arbitrary direction by Shaohua Chen; Tzuchiang Wang (363-369).
In this paper, a generalized JKR model is investigated, in which an elastic cylinder adhesively contacts with an elastic half space and the contact region is assumed to be perfect bonding. An external pulling force is acted on the cylinder in an arbitrary direction. The contact area changes during the pull-off process, which can be predicted using the dynamic Griffith energy balance criterion as the contact edge shifts. Full coupled solution with an oscillatory singularity is obtained and analyzed by numerical calculations. The effect of Dundurs' parameter on the pull-off process is analyzed, which shows that a nonoscillatory solution can approximate the general one under some conditions, i.e., larger pulling angle ( π / 2 is the maximum value), smaller a / R or larger nondimensional parameter value of Δ γ / E ∗ R . Relations among the contact half width, the external pulling force and the pulling angle are used to determine the pull-off force and pull-off contact half width explicitly. All the results in the present paper as basic solutions are helpful and applicable for experimenters and engineers.Generalized plain strain JKR model is investigated, in which the adhesive contact region is assumed to be perfect bonding with an external pulling force acting on the cylinder in an arbitrary direction. Basic solutions are obtained, which is applicable for experimenters and engineers.
Keywords: Generalized JKR model; Adhesion; Perfect bonding interface; Contact mechanics; Arbitrary direction; Basic solution;
Preparation of silver nanoparticles in water-in-oil AOT reverse micelles by Wanzhong Zhang; Xueliang Qiao; Jianguo Chen; Hongshui Wang (370-373).
Colloidal silver nanoparticles were synthesized in AOT microemulsions. The effects of the precursors' concentration and the molar ratios of water to AOT on the particle size and size distribution were investigated. UV–vis spectra showed that the Ag+ 4 intermediates formed at low N2H4 concentration. TEM micrographs confirmed that the silver nanoparticles are all spherical with mean diameters in the range 2–5 nm and have a narrow size distribution. Not only the particle size but also the size distribution was increasing with the W value. The silver colloid has favorable stability and can be preserved for a long time without precipitation.The silver nanoparticles were synthesized by AOT–dodecane–H2O microemulsion. Transmission electron microscopy (TEM) and UV–vis spectroscopy were used to characterize the resultant silver colloid. The Ag+ 4 intermediates formed at early stages of the reaction and then the clusters grew or aggregated to form larger nanoparticles. The silver nanoparticles are all spherical with mean diameters in the range 2–5 nm and have a narrow size distribution as well as good stabilization. With the W values increasing, both the average size and the size distribution increased obviously.
Keywords: Silver; Nanoparticles; AOT; Microemulsion;
Spontaneous spreading of surfactant-bearing drops in the sorption-controlled limit by Kit Yan Chan; Ali Borhan (374-377).
Axisymmetric spreading of a liquid drop containing a soluble surfactant on a smooth solid substrate is numerically investigated for the case in which surfactant mass transfer between the interface and the bulk liquid is sorption/kinetic controlled. The fastest spreading rate is achieved by drops with O ( 1 ) values of Biot number for which the rate of surface convection is comparable to the sorption rate, and the surfactant molecules transferred to the interface are effectively convected to the contact line region.The fastest spreading rate is achieved by drops with O ( 1 ) values of Biot number for which the rate of surface convection is comparable to the sorption rate.
Keywords: Surfactants; Drops; Spreading; Marangoni stress;
by Arthur Hubbard (378).