Journal of Colloid And Interface Science (v.305, #2)
Editorial Board (CO1).
Control of pertechnetate sorption on activated carbon by surface functional groups by Yifeng Wang; Huizhen Gao; Rakesh Yeredla; Huifang Xu; Mike Abrecht (209-217).
The isotope 99Tc is highly soluble and poorly adsorbed by natural materials under oxidizing conditions, thus being of particular concern for radioactive waste disposal. Activated carbon can potentially be used as an adsorbent for removing Tc from aqueous solutions. We have tested six commercial activated carbon materials for their capabilities for sorption of pertechnetate (TcO− 4). The tested materials can be grouped into two distinct types: Type I materials have high sorption capabilities with the distribution coefficients ( K d ) varying from 9.5 × 10 5 to 3.2 × 10 3 ml / g as the pH changes from 4.5 to 9.5, whereas type II materials have relatively low sorption capabilities with K d remaining more or less constant (1.1 × 103–1.8 × 103 ml/g) over a similar pH range. The difference in sorption behavior between the two types of materials is attributed to the distribution of surface functional groups. The predominant surface groups are identified as carboxylic and phenolic groups. The carboxylic group can be further divided into three subgroups, A, B, and C, in the order of increasing acidity. The high sorption capabilities of type I materials are found to be caused by the presence of a large fraction of carboxylic subgroups A and B, while the low sorption capabilities of type II materials are due to the exclusive presence of phenolic and carboxylic subgroup C. Therefore, the performance of activated carbon for removing TcO− 4 can be improved by enhancing the formation of carboxylic subgroups A and B during materials processing.Six commercial activated carbon materials have been tested for their capabilities ( K d ) for sorption of pertechnetate (TcO− 4). The results show that the materials can be grouped into two general types with very distinct sorption behaviors, which can be attributed to the different distributions of functional groups on material surfaces.
Keywords: Activated carbon; Carbonaceous material; Technetium; Pertechnetate; Surface functional group; Mesoporous material; Adsorption; Oxyanion;
Effect of operating conditions on the removal of Pb2+ by microporous titanosilicate ETS-10 in a fixed-bed column by Lu Lv; Kean Wang; X.S. Zhao (218-225).
The breakthrough behavior of Pb2+ in an ETS-10 fixed bed was experimentally examined at various operating conditions. Results showed that the adsorption amount of Pb2+ ions per unit mass of ETS-10 particles in a column is about 1.68 mmol/g under the experimental conditions. This amount was not markedly affected by the operating conditions because of the rapid adsorption rate of Pb2+ ions on ETS-10. In the presence of competitive metal ions, the amount of Pb2+ adsorbed on ETS-10 was slightly reduced. An overshoot of the effluent concentrations of competitive metal ions Cu2+ and Cd2+ was observed in the adsorption systems of binary and ternary solutions. This is ascribed to the replacement of pre-adsorbed Cu2+ and Cd2+ ions by Pb2+ ions. The ETS-10 column broken up by Pb2+ ions can be regenerated by using an EDTA-Na2 solution and the regenerated column can be reused.
Keywords: Microporous titanosilicate ETS-10; Heavy metal ions; Fixed bed; Adsorption; Regeneration;
Field-induced adsorption exclusion of particles from one-dimensional nanomagnets by L.E. Helseth (226-228).
I study the adsorption of paramagnetic colloids to one-dimensional nanomagnets. It is found that in the absence of external magnetic fields the colloids tend to adsorb to the nanomagnet by arranging themselves in a nearly close-packed formation, whereas in an external field some of the colloids are repelled due to dipolar interactions. I develop a theory for this phenomenon and show that it is in agreement with experimental data.The figure shows some colloids being attached to a one-dimensional domain wall, while others approaching the domain wall are pushed away due to dipolar repulsions.
Keywords: Adsorption; Paramagnetic colloids;
Simultaneous uptake of Ni2+, NH+ 4 and PO3− 4 by amorphous CaO–Al2O3–SiO2 compounds by Kiyoshi Okada; Megumi Shimazu; Yoshikazu Kameshima; Akira Nakajima; Kenneth J.D. MacKenzie (229-238).
Simultaneous uptake of Ni2+, NH+ 4, and PO3− 4 by amorphous CaO–Al2O3–SiO2 (C-A-S) compounds was investigated using batch and column methods. Fifteen different C-A-S samples with systematically varied chemical compositions were prepared by coprecipitation from ethanol–water solutions containing Ca(NO3)2⋅4H2O, Al(NO3)3⋅9H2O, and Si(OC2H5)4, using NH4OH as the precipitating agent. The resulting precipitates were dried and heated at various temperatures to produce the C-A-S samples, which were then characterized by XRD, FTIR, solid state MAS NMR, DTA-TG, and N2 adsorption. All the C-A-S samples prepared at 600–900 °C were amorphous, apart from the CaO-rich samples. Simultaneous uptake of Ni2+, NH+ 4, and PO3− 4 was determined by a batch method using a solution with an initial concentration of 2 mM. In these experiments, the uptake abilities of the C-A-S samples for Ni2+ and PO3− 4 were high, but were relatively low for NH+ 4. The uptake abilities for Ni2+ and PO3− 4 increased but that for NH+ 4 decreased as the silica content in the C-A-S decreased, suggesting that similar uptake mechanisms (ion substitution and/or precipitation) are operating for Ni2+ and PO3− 4, but the uptake mechanism for NH+ 4 is different (physical adsorption). The column experiments indicate that the order of uptake ability of C-A-S for the three ions is NH+ 4 ≪ PO3− 4 < Ni2+. Although the silica content of the C-A-S does not have the expected influence on the uptake of these three ions, for NH+ 4 it plays an important role in the formation of the amorphous phase and also in the suppression of Ca2+ and/or Al3+ release from the C-A-S during the uptake experiments. The optimum uptake properties of the C-A-S can thus be controlled by adjusting the chemical compositions and heating conditions under which the samples are prepared.Amorphous CaO–Al2O3–SiO2 compounds show good simultaneous uptake abilities for cations and anions and the uptake is NH+ 4 ≪ PO3− 4 < Ni2+ in order.
Keywords: Simultaneous uptake; Calcium aluminosilicate; Heavy metal ion; Phosphate ion; Ammonium ion;
A water-activated pump for portable microfluidic applications by Brian T. Good; Christopher N. Bowman; Robert H. Davis (239-249).
An on-chip micropump for portable microfluidic applications was investigated using mathematical modeling and experimental testing. This micropump is activated by the addition of water, via a dropper, to ionic polymer particles that swell due to osmotic effects when wetted. The resulting particle volume increase deflects a membrane, forcing a separate fluid from an adjacent reservoir. The micropump components, along with the microfluidic components, are fabricated using the contact liquid photolithographic polymerization (CLiPP) method. The maximum flow rate achieved with this pump is 17 μL per minute per mg of dry polymer particles of 355–425 μm in diameter. The pump flow rate may be controlled by adjusting the particle size and amount, the membrane properties, and the channel dimensions. The experimental results demonstrate good agreement with an analytical model describing the particle swelling and its coupling with resistive forces from the bending membrane, viscous flow in the microchannel, and interfacial effects. Key features of this micropump are that it can be placed directly on a microdevice, and that it requires only a small amount of water and no external power supply to function. Therefore, this pumping system is useful for applications in which a highly portable device is required.Fluid-responsive polymer particles are used to actuate a microfluidic pumping system. The particles swell when wetted, thereby stretching a flexible membrane and driving fluid from an adjacent reservoir.
Keywords: Hydrogels; Displacement micropump; Microactuators; Polymer microfluidic devices; CLiPP;
Interfacial assembly of a phospholipid Langmuir monolayer by electrodeposited silver colloids by Claire Mangeney; Vincent Dupres; Sophie Bernard (250-255).
Two-dimensional nanostructured silver films were electrodeposited at the surface of a silver nitrate subphase coated by a negatively charged dimyristoylphosphatidylglycerol (DMPG) Langmuir monolayer. The modifications of the phospholipid interfacial organization generated by the growing colloidal silver film were investigated using surface pressure–time isotherms and grazing incidence X-ray diffraction experiments (GIXD). A decrease in the initial surface pressure of the DMPG monolayer is observed outside of the growing silver film, followed by a stabilization of the surface pressure when the radius of the metallic layer reaches its plateau value. This behavior is attributed to the compression of the DMPG molecules above the silver film and to the correlated relaxation and expansion of those outside the silver film area as recorded by a Wilhelmy pressure sensor. GIXD experiments further evidenced the contraction of the phospholipid monolayer above the electrochemically growing films. Indeed, the diffraction spectra show a shift in the peak position toward higher values of the in-plane component of the wave-vector transfer, indicating a closer packing of the DMPG alkyl chains. This is also in agreement with the observed loss of the chain tilt angle, suggesting that the colloidal silver film induces interfacial structuring of the DMPG monolayer.We studied the modifications of the phospholipid interfacial organization generated by a two-dimensional silver electrodeposition. Grazing incidence X-ray diffraction experiments demonstrate the contraction of the phospholipid monolayer on top of the silver film.
Keywords: Langmuir monolayer; Silver electrodeposit; Phospholipid; Grazing incidence; X-ray diffraction;
Cationic latex formation by ionic modification by Heloisa Cajon Schumacher; Marilene Alves; Carlos Alberto Paula Leite; Juliane Pereira Santos; Érico Teixeira Neto; Mauro Makoto Murakami; Fernando Galembeck; Marcelo do Amaral (256-263).
Stable cationic latices were prepared by charge inversion of anionic styrene–acrylic copolymer latices upon binding Al3+ and Fe3+ ions. This is achieved by stabilizing the latices with a high-HLB (hydrophile–lypophile balance) nonionic surfactant that imparts strong steric stability to the latex, even in the presence of high concentrations of multivalent counterions while these are bound to the latex anionic sites. The cationic latices thus prepared have good stability properties, and the same procedure should be applicable to essentially any latex-carrying anionic sites. Analytical ESI-TEM images show that particle-bound iron is concentrated at the particle borders, but it is also found in the particle bulk.Stable cationic latexes were prepared by charge inversion of anionic styrene–acrylic copolymer latexes, stabilized by nonionic surfactants, upon binding Al3+ and Fe3+ ions.
Keywords: Cationic latex; Charge inversion; Fe3+ ion; Al3+ ion; Anionic latices; Nonionic surfactant; Zeta potential; Surfactant adsorption;
Fluorescent tetraruthenated porphyrins embedded in monolithic SiO2 gels by the sol–gel process by Shirleny F. Santos; Marcelo L. Santos; Luis E. Almeida; Nivan B. Costa; Iara F. Gimenez; Koiti Araki; Ildemar Mayer; Fabio Monaro Engelmann; Henrique Eisi Toma; Ledjane S. Barreto (264-269).
In this work silica gels have been prepared by a sol–gel method using tetraethylorthosilicate as gel precursor. The tetraruthenated porphyrins H2(3-TRPyP), Co(3-TRPyP), and H2(4-TRPyP) were incorporated into the systems during gel formation without problems commonly found in the process, such as aggregation. Spectroscopic studies of the resulting silica gels revealed the presence of absorption bands in the range 200–400 nm associated with the transitions of the groups ruthenium–bipyridine, along with the Soret band at the same wavelengths observed in solution. The porphyrins were found to preserve fluorescence emission properties in the range 650–700 nm even after the aging period. Study of the thermal behavior and decomposition kinetics evidenced that the porphyrin H2(4-TRPyP) is the least stable of the group and that all compounds decompose according to first-order kinetics.Tetraruthenated porphyrins have been embedded in SiO2 gels by the sol–gel process, with preservation of the fluorescence emission properties. No aggregation, protonation, or decomposition has been observed during the sol–gel process, owing to the chemical nature of the tetraruthenated porphyrins, which are compatible with the reaction medium of the sol–gel process.
Keywords: Sol–gel gel; Spectroscopic study; Tetraruthenated porphyrins; Hybrid material;
Adsorption orientations and interactions of methyl orange on negatively and positively charged colloidal silver particles by Aiping Zhang; Yan Fang (270-274).
Both positively and negatively charged colloidal silver particles were prepared from chemical deoxidized methods. Then UV–visible absorption, fluorescence, and surface-enhanced Raman scattering of methyl orange adsorbed onto surfaces of these two kinds of particles were observed and compared with each other. The results indicate that dye molecules may adsorb onto these two kinds of silver surface in differing adsorption orientations with different interactions, which caused the different phenomena.
Keywords: Methyl orange; Silver particles; Adsorption orientation; Spectroscopy;
Mesoporous silica reinforced by silica nanoparticles to enhance mechanical performance by Jen-Tsung Luo; Hua-Chiang Wen; Yu-Ming Chang; Wen-Fa Wu; Chang-Pin Chou (275-279).
Silica nanoparticle/mesoporous silica composite films were prepared by direct mixing with mechanical stirring and thermal imidization. The structural morphology was elucidated by scanning electron microscopy and the surface of the film was imaged by atomic force microscopy. The functional groups and desorption process of the films were elucidated by Fourier transform infrared spectroscopy and thermal desorption spectroscopy. The mechanical properties were investigated using a nanoindenter system. The gel matrix and the filler are very compatible because they have similar molecular content. The composite films had a higher mechanical strength than pure porous silica film. Their strength is related to the silica nanoparticle content. The interfacial compatibility, dispersion effect, and interfacial strength also affect the mechanical strength of composite films.
Keywords: Porous silica; Nanoparticle; Composite material; Mechanical properties;
NMR cryoporometry with octamethylcyclotetrasiloxane as a probe liquid. Accessing large pores by D. Vargas-Florencia; O.V. Petrov; I. Furó (280-285).
Octamethylcyclotetrasiloxane is presented and investigated as probe liquid for NMR cryoporometry or DSC-based thermoporometry. This compound which may imbibe into both hydrophilic and hydrophobic pores is shown to exhibit a melting point depression that is larger than that for other cryoporometric probe materials such as cyclohexane. The transverse relaxation time differs by more than three orders of magnitude between the solid and liquid states, separated by a sharp phase transition. Hence, as demonstrated in controlled pore glasses, octamethylcyclotetrasiloxane can provide pore size distributions for materials with pore sizes up to the micrometer range.Pore size distribution for pores up to μm size can be obtained by NMR cryoporometry with octamethylcyclotetrasiloxane, as demonstrated by experiments in controlled pore glasses.
Keywords: Cryoporometry; Thermoporometry; NMR; DSC; Phase transition; Melting point; Pore size; Pore size distribution;
Interfacial interactions between hydrocarbon liquids and solid surfaces used in mechanical oil spill recovery by Victoria Broje; Arturo A. Keller (286-292).
The goal of this research was to study wetting and adhesion processes between various petroleum products and solid surfaces. When a liquid interacts with a solid surface, wetting, spreading and adhesion processes determine its behavior. These processes are of great importance for understanding oil spill response as well as oil spill behavior on land and in near shore environments, and oil extraction from the reservoir rock. The current study aimed at analyzing oil affinity and adhesion to surfaces used in the mechanical recovery of oil spills. A number of crude oils and petroleum products were tested with the surface materials that are used or may potentially be used to recover oil spills. Through the study of contact angles and recovered mass, it was found that the behavior of the oils at the solid surface is largely determined by the roughness of the solid. For smooth solids, contact angle hysteresis is a good indicator of the ability of the solid to retain oil. For rougher elastomers, the advancing contact angle can be used to predict wetting and adhesion processes between oil and solid. This study showed that oleophilic elastomers (e.g., Neoprene and Hypalon) have higher oil recovery potential than smooth polymers.The current study aimed at analyzing oil affinity and adhesion to surfaces used in the mechanical recovery of oil spills.
Keywords: Contact angle; Adhesion; Oil; Mechanical recovery; Spreading; Wilhelmy plate; Skimmer;
Self-assembly of tetradecyltrimethylammonium bromide in glycerol aqueous mixtures: A thermodynamic and structural study by C. Carnero Ruiz; L. Díaz-López; J. Aguiar (293-300).
In this paper, we have studied the effect of glycerol on the micelle formation of tetradecyltrimethylammonium bromide. Changes in both the critical micelle concentration and the degree of counterion binding of the surfactant upon the addition of glycerol across a temperature range (20–40 °C) were examined by using the conductance method. The equilibrium model of micelle formation was applied to obtain the thermodynamic parameters of micellization. An enthalpy–entropy compensation effect was observed in all the solvent systems, but whereas the micellization of the surfactant in the medium with 20% glycerol occurs under the same structural conditions as in pure water, in glycerol rich mixtures the results suggest that the lower aggregation in these media is due to the minor cohesive energy of the solvent system in relation to water. It was also observed that the micellar aggregation number, as obtained by the static quenching method, decreases with the glycerol content. This fact was attributed to an increase in the surface area per headgroup of the surfactant as a consequence of an enhanced solvation, probably induced by the incorporation of some glycerol molecules in the micellar solvation layer. Although the pyrene 1:3 ratio index does not indicate significant changes in the micropolarity at the micelle–bulk interface, the data of fluorescence anisotropy of coumarin 6 and fluorescein are compatible with the formation of a more compact solvation layer.
Keywords: Tetradecyltrimethylammonium bromide; Micellization; Glycerol–water mixtures; Conductance; Fluorescence probe studies;
Thermodynamics of aqueous solutions of dodecyldimethylethylammonium bromide by Emilia Fisicaro; Mariano Biemmi; Carlotta Compari; Elenia Duce; Monica Peroni (301-307).
The thermodynamic properties of the aqueous solutions of dodecyldimethylethylammonium bromide (DEDAB) were determined as a function of concentration by means of direct methods. Dilution enthalpies at 298 and 313 K, densities and sound velocities at 298 K were measured, allowing the determination of apparent and partial molar enthalpies, volumes, heat capacities and compressibilities. Changes in thermodynamic quantities upon micellization were derived using a pseudo-phase transition approach. These data allow for the determination of the effect of the ―CH2 ― group, when added to the polar head of alkyltrimethylammonium bromides. The properties mainly affected by this addition are the enthalpies and, as a consequence, the entropies. The lowering of the charge density on the quaternary nitrogen due to the inductive effect of the ethyl group, greater than that of the methyl one, raises the plateau value of apparent and molar enthalpy by a quantity similar to that due to the removing of a methylene group from the hydrophobic chain. This effect does not play a great role in the value of the cmc (i.e. on the free energy of micelle formation), since the small decrease in cmc of DEDAB compared to DTAB reflects the increase in the overall hydrophobicity of the molecule. Volumes of DEDAB are greater than those of DTAB by about 15 cm3 mol−1, both at infinite dilution and at micellar phase, a value in agreement with that generally accepted for a methylene group. The trends of apparent molar heat capacities and compressibilities vs m are the same as for DTAB: in fact, these quantities are related to the number of water molecules involved in the hydrophobic processes in solution, not very greatly affected by the substitution of a methyl group by an ethyl one on the polar head. In summary, this substitution affects to a significant extent the first derivatives of the free energy, but does not affect the second derivatives.Thermodynamics of the aqueous solutions of dodecyldimethylethylammonium bromide (DEDAB) were determined vs concentration by means of direct methods. Changes in thermodynamic quantities upon micellization were derived using a pseudo-phase transition approach.
Keywords: Dodecyldimethylethylammonium bromide; Apparent and partial molar enthalpies of; Apparent molar heat capacities of; Apparent molar volumes of; Apparent molar compressibilities of; Micellization thermodynamic parameters of; Dilution heats of;
Effect of ionic surfactants on the iridescent color in lamellar liquid crystalline phase of a nonionic surfactant by Xinjiang Chen; Hiroyuki Mayama; Goh Matsuo; Tsukasa Torimoto; Bunsho Ohtani; Kaoru Tsujii (308-314).
A nonionic surfactant, n-dodecyl glyceryl itaconate (DGI), self-assembles into bilayer membranes in water having a spacing distance of sub-micrometer in the presence of small amounts of ionic surfactants, and shows beautiful iridescent color. Ionic surfactants have strong effects on this iridescent system. We have interestingly found that the iridescent color changes with time after mixing DGI and ionic surfactants and the color in equilibrium state changes greatly with concentration of the ionic surfactants. The time-dependent color change results from the transformation of DGI aggregate structure after being mixed with ionic surfactant. It is first found that the iridescent color of this nonionic system can be changed from red to deep blue by altering the concentration of ionic surfactants added even though the total concentration of surfactant is almost constant. Such large blue shift of the iridescent color in equilibrium state cannot be fully explained by the ordinary undulation theory applied so far for this phenomenon. The flat lamellar sheets tend to curve by increasing the concentration of ionic surfactants to form separated onion-like and/or myelin-like structures. These separated structures of lamellar system result in the decrease of spacing distance between bilayer membranes because some vacant spaces necessarily appear among these structures.Iridescent color change of a nonionic surfactant with small concentration change of ionic surfactant.
Keywords: Bilayer membrane; Iridescent color; Helfrich thermal undulation; Liquid crystal; Lamellar sheet; Lamellar vesicle;
Effect of surface interaction of silica nanoparticles modified by silane coupling agents on viscosity of methylethylketone suspension by Motoyuki Iijima; Mayumi Tsukada; Hidehiro Kamiya (315-323).
In order to control the viscosity of a dense silica methylethylketone (MEK) suspension, the surfaces of silica nanoparticles were modified by 3-glycidoxypropyltrimethoxysilane (GPS) or hexyltrimethoxysilane (C6S) in MEK with the addition of a small amount of pH-controlled water. First, the effect of water addition on the amount of chemisorbed coupling agent was investigated. pH-controlled water enhanced the reactivity of the coupling agent in MEK. The amount of chemisorbed coupling agent increased slightly with the addition of pH 3 water and increased remarkably with the addition of pH 12 water. Next, the effect of the organic functional groups of the coupling agent, pH of the additive water, and additive amount of coupling agent on surface interaction were determined by colloid probe AFM. The steric repulsive force between the silica nanoparticles increased due to water addition, particularly when the pH was maintained at 3. The viscosity of the silica MEK suspension reduced effectively when this repulsive force appeared; however, the optimum condition for reducing the suspension viscosity was dependent on the coupling agent species. The viscosity of the dense silica MEK suspension can be controlled by the addition of small amounts of pH-controlled water and the functional groups of the coupling agent.Surface interaction forces and suspension viscosities were dependent on the polymerized structures of silane coupling agents on the surface of silica nanoparticles that were controlled by the pH of additive water in MEK.
Keywords: Silica; Methylethylketone; AFM; Colloid probe; Hexyltrimethoxysilane; 3-Glycidoxypropyltrimethoxysilane; Surface force; Viscosity;
Evaluation of the electric force in electrophoresis by Jyh-Ping Hsu; Li-Hsien Yeh; Ming-Hong Ku (324-329).
A new expression for the evaluation of the electric force acting on a colloidal particle in an applied electric field is derived under the condition of weak applied electric field. The expression derived, which is based on the Maxwell stress tensor, is applicable to both rigid and soft particles for various types of surface conditions and to both symmetric and asymmetric geometries. We show that, depending upon the electrophoresis conditions, the electric force evaluated by the methods commonly used in the literature can be overestimated, thereby leading to incorrect electrophoretic mobility.Electrophoresis under general conditions when a boundary is present.
Keywords: Electrophoretic mobility; Maxwell stress tensor; Various types of charged conditions;
PEG400 novel phase description in water by Nawal Derkaoui; Sylvère Said; Yves Grohens; René Olier; Mireille Privat (330-338).
The behavior of hydroxyl-terminated PEG400 in water was investigated by surface tension measurements and 13C NMR as a function of concentration and temperature. PEG400 exhibited a critical aggregative concentration (cac) that evidenced both its amphiphilic character and its aggregation capacity. Moreover, the chemical shifts of the different carbons of the PEG were followed by NMR versus concentration at various temperatures. We observed a plateau between 20 and 35 °C at concentrations above 0.2 mol L−1 and ascribed it to the aggregation process. A good correlation was found between the NMR spectra in the region of aggregation and the cac region in the phase diagram. Our investigations were also focused on the solid–liquid region of the phase diagram at lower temperatures. These experimental data, together with conclusions available in the literature, led us to propose explanations for the conformation/hydration/aggregation in the PEG400–water solutions phenomena.PEG400 was found to exhibit a critical aggregation concentration (cac) showing both its amphiphilic character and its aggregation capacity. A good correlation was found between the NMR spectra in the region of aggregation and the cac data.
Keywords: PEG; Aqueous solutions; Aggregation; Helical structure;
Self-assembly of Co-based nanosheets into novel nest-shaped nanostructures: Synthesis and characterization by Jie Zhang; Zhihui Dai; Jianchun Bao; Ning Zhang; M. Arturo López-Quintela (339-344).
We report the first observation of the formation of novel Co-based three-dimensional (3D) self-assembly hollow nanostructures, i.e., nest-shaped nanospheres composed of sheet-like particles, via reduction of cobalt salt with sodium tetrahydroboride in cetyltrimethylammonium bromide (CTAB)–cyclohexane–NH4F aqueous solutions. It was found that the cyclohexane has a significant influence on the formation of the nest-shaped Co-based nanospheres, because when the experiments are carried out in the absence of cyclohexane, only sheet-like particles are formed. NH4F plays also an important role in the formation of the hollow nanostructures because without this salt mainly solid spherical structures, composed of sheet-like particles, instead of nest-shaped structures are obtained. The nanostructures are mainly formed by Co, but also a minor amount (17%) of Co2B is present in the final compounds. The structures are characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and field-emission scanning electron microscopy (FESEM). A possible mechanism for the formation of the novel Co-based nanostructures is proposed.Synthesis of novel nest-shaped Co-based nanospheres, composed of sheet-like particles, is reported. A possible mechanism for the formation of these nanostructures is put forward.
Keywords: Co; Self-assembly; Cetyltrimethylammonium bromide; Vesicle;
Preparation of crystalline gold nanoparticles at the surface of mixed phosphatidylcholine–ionic surfactant vesicles by Daniela Robertson; Brigitte Tiersch; Sabine Kosmella; Joachim Koetz (345-351).
The formation of gold nanoparticles and the crystal growth at the surface of mixed phosphatidylcholine (PC)–ionic surfactant vesicles was investigated. The PC-bilayer surface was negatively charged by incorporating sodium dodecyl sulfate (SDS) and positively charged by adding hexadecyltrimethylammonium chloride (CTAB). The mass ratio phosphatidylcholine:surfactant was fixed in both cases at 1:1. The gold nanoparticle formation was studied by using transmission electron microscopy (TEM) combined with dynamic light scattering (DLS) and UV–vis absorption spectroscopy. TEM micrographs confirm that the particle formation occurs on the vesicle surface. However, the reduction process depends on the ionic surfactant incorporated into the vesicles, the vesicle size distribution, as well as the temperature used for the reduction process. Thereby, it becomes possible to control the crystal growth of the individual spherical gold nanoparticles in a characteristic way. Red colored colloidal dispersions consisting of monodisperse spherical nanoparticles with an average particle size between 2 and 8 nm (determined by dynamic light scattering) can be obtained by using a monodisperse SDS-modified vesicle phase. When the temperature is increased to 45 °C, a crystallization in rod-like or triangular structures is observed. In the CTAB-based template phase in general larger gold particles of about 35 nm are formed. In similarity to the anionic vesicles a temperature increase leads to the crystallization in triangular structures.
Keywords: Phosphatidylcholine; Vesicles; Gold nanoparticles;
Surface energy of talc and chlorite: Comparison between electronegativity calculation and immersion results by Jean-Marc Douillard; Fabrice Salles; Marc Henry; Harold Malandrini; Frédéric Clauss (352-360).
The surface energies of talc and chlorite is computed using a simple model, which uses the calculation of the electrostatic energy of the crystal. It is necessary to calculate the atomic charges. We have chosen to follow Henry's model of determination of partial charges using scales of electronegativity and hardness. The results are in correct agreement with a determination of the surface energy obtained from an analysis of the heat of immersion data. Both results indicate that the surface energy of talc is lower than the surface energy of chlorite, in agreement with observed behavior of wettability. The influence of Al and Fe on this phenomenon is discussed. Surface energy of this type of solids seems to depend more strongly on the geometry of the crystal than on the type of atoms pointing out of the surface; i.e., the surface energy depends more on the physics of the system than on its chemistry.A calculation is performed in order to obtain the solid surface tension of ideal crystals of talc and chlorite. From this result, it is possible, using thermodynamic models, to calculate the heat of immersion in water of these solids and to compare with experimental data obtained for well-known samples. Results are in good agreement, confirming the differences between surfaces of talc and chlorite and confirming that a route of calculation of surface tension using electronegativity equalization is correct, even though it is very simple.
Keywords: Talc; Chlorite; Atomic charges; Electronegativity; Hardness; Surface energy; Immersion;
Enhanced aqueous solubilization of tetrachloroethylene by a rhamnolipid biosurfactant by Joseph S. Clifford; Marios A. Ioannidis; Raymond L. Legge (361-365).
A rhamnolipid biosurfactant produced by Pseudomonas aeruginosa ATCC 9027 was isolated, purified and characterized in terms of its ability to mobilize and solubilize tetrachloroethylene (PCE) for potential use in surfactant-enhanced aquifer remediation (SEAR) applications. Using a drop volume method, the PCE–biosurfactant steady-state interfacial tension was determined and found to be ca. 10 mN/m which is not low enough to cause significant PCE nonaqueous phase liquid (NAPL) mobilization. It was observed that the biosurfactant partitioned significantly into PCE at aqueous concentrations higher than the critical micelle concentration (CMC). After accounting for rhamnolipid partitioning into the PCE phase, a weight solubilization ratio (WSR) of 1.2 gPCE/grhamnolipid was determined and through this mechanism the biosurfactant significantly improved the apparent aqueous solubility of PCE.After accounting for rhamnolipid partitioning into the PCE phase, a WSR of 1.2 was determined and through this mechanism the biosurfactant significantly improved the apparent aqueous solubility of PCE.
Keywords: Biosurfactant; Distribution coefficient; Interfacial tension; Pseudomonas aeruginosa; Rhamnolipid; Tetrachloroethylene;
Facile synthesis of superparamagnetic magnetite nanoparticles in liquid polyols by Wei Cai; Jiaqi Wan (366-370).
Magnetite nanoparticles have been successfully synthesized in liquid polyols at elevated temperature. Polyol solvent plays a crucial role in determining the morphology and colloidal stability of the resulting particles. The structure and morphology of the nanoparticles were studied using XRD, TEM, SAED, TGA and FTIR. The magnetic properties of the samples were measured using physical properties measurement system (PPMS) of Quantum Design. The results show that as-prepared magnetite nanoparticles are monodisperse, highly crystalline and superparamagnetic at room temperature. The nanoparticles can be easily dispersed in aqueous media and other polar solvents due to coated by a layer of hydrophilic polyol ligands in situ. This approach provides a facile route to prepare magnetite nanoparticles.Monodisperse water-soluble magnetite nanoparticles were synthesized by the one-pot decomposition of iron(III) acetylacetonate in triethylene glycol. As-prepared nanoparticles have nearly spherical shapes and narrow size distribution and can be well re-dispersed in water due to coated a layer of hydrophilic triethylene glycol on the surface of the particles in situ.
Keywords: Magnetite nanoparticles; Polyol process; Synthesis; Superparamagnetic; Water-soluble;
by Arthur Hubbard (371).
Author Index for Volume 305 (373-374).