Advances in Colloid and Interface Science (v.142, #1-2)
Editorial Board (iii).
Viscosities of liquids, colloidal suspensions, and polymeric systems under zero or non-zero electric field by Tian Hao (1-19).
The viscosities of pure liquids, polymer solutions and melts, and colloidal suspensions under zero or non-zero electric field are surveyed in this paper and the focus is placed on the case that no electric field is applied. The free volume concept and Eyring's rate theory is used for deriving the viscosity equations of pure liquids, polymer solutions and melts, and colloidal suspensions. The derived equations are found to be more universal and could be reduced to many currently used equations under certain simplifications. Qualitatively, those derived equations are in consistent with experimental results, too.
Mapping the surface (hydr)oxo-groups of titanium oxide and its interface with an aqueous solution: The state of the art and a new approach by George D. Panagiotou; Theano Petsi; Kyriakos Bourikas; Christos S. Garoufalis; Athanassios Tsevis; Nikos Spanos; Christos Kordulis; Alexis Lycourghiotis (20-42).
In this article the “titanium oxide/electrolyte solution” interface is studied by taking in advantage the recent developments in the field of Surface and Interface Chemistry relevant to this oxide.Ab-initio calculations were performed in the frame of the DFT theory for estimating the charge of the titanium and oxygen atoms exposed on the anatase (1 0 1), (1 0 0), (0 0 1), (1 0 3) f and rutile (1 1 0) crystal faces. These orientations have smaller surface energy with respect to other ones and thus it is more probable to be the real terminations of the anatase and rutile nanocrystallites in the titania polycrystalline powders. Potentiometric titrations for obtaining “fine structured” titration curves as well as microelectrophoresis and streaming potential measurements have been performed.On the basis of ab-initio calculations, and taking into account the relative contribution of each crystal face to the whole surface of the nanocrystals involved in the titania aggregates of a suspension, the three most probable surface ionization models have been derived. These models and the Music model are then tested in conjunction with the “Stern–Gouy–Chapman” and “Basic Stern” electrostatic models. The finally selected surface ionization model (model A) in combination with each one of the two electrostatic models describes very well the protonation/deprotonation behavior of titania. The description is also very good if this model is combined with the Three Plane (TP) model.The application of the “A/(TP)” model allowed mapping the surface (hydr)oxo-groups [TiO(H) and Ti2O(H)] of titania exposed in aqueous solutions. At pH > pzc almost all terminal oxygens [TiO] are non-protonated whereas even at low pH values the non-protonated terminal oxygens predominate. The acid-base behavior of the bridging oxygens [Ti2O] is different. Thus, even at pH = 10 the greater portion of them is protonated.The application of the “A/TP” model in conjunction with potentiometric titrations, microelectrophoresis and streaming potential experiments allowed mapping the “titania/electrolyte solution” interface. It was found that the first (second) charged plane is located on the oxygen atoms of the first (second) water overlayer at a distance of 1.7 (3.4) Å from the surface. The region between the surface and the second plane is the compact layer. The region between the second plane and the shear plane is the stagnant diffuse part of the interface, with an ionic strength dependent width, ranging from 20 (0.01 M) up to 4 Å (0.3 M). The region between the shear plane and the bulk solution is the mobile diffuse part, with an ionic strength dependent width, ranging from 10 (0.01 M) up to 2 Å (0.3 M).At I > 0.017 M the mean concentration of the counter ions is higher in the stagnant than in the mobile part of the diffuse layer. For a given I, removal of pH from pzc brings about an increase of the mean concentration in the interfacial region and a displacement of the counter ions from the mobile to the stagnant part of the diffuse layer. The mean concentration of the counter ions in the compact layer is generally lower than the corresponding ones in the stagnant and mobile diffuse layers. The mobility of the counter ions in the stagnant layer decreases as pH draws away from pzc or ionic strength increases.
Keywords: Titania; Titanium oxide; Preparation of supported catalysts; Surface sites; (Hydr)oxo-groups; Hydroxyls; Density functional theory (DFT); Crystal face; Anatase; Rutile; Outersphere; Complexation; Electrolyte; Adsorption; Deposition; Ion pairs; Double layer; Interface; Adsorbed water; Surface charge; Zeta potential; PZC; IEP; Titration; Microelectrophoresis; Streaming potential;
Polyelectrolyte-coated liposomes: Stabilization of the interfacial complexes by Alexander A. Yaroslavov; Anna A. Rakhnyanskaya; Ekaterina G. Yaroslavova; Anna A. Efimova; Fredric M. Menger (43-52).
Anionic liposomes, composed of egg lecithin (EL) or dipalmitoylphosphatidylcholine (DPPC) with 20 mol% of cardiolipin (CL2−), were mixed with cationic polymers, poly(4-vinylpyridine) fully quaternized with ethyl bromide (P2) or poly-l-lysine (PL). Polymer/liposome binding studies were carried out using electrophoretic mobility (EPM), fluorescence, and conductometry as the main analytical tools. Binding was also examined in the presence of added salt and polyacrylic acid (PAA). The following generalizations arose from the experiments: (a) Binding of P2 and PL to small EL/CL2− liposomes (60–80 nm in diameter) is electrostatic in nature and completely reversed by addition of salt or PAA. (b) Binding can be enhanced by hydrophobization of the polymer with cetyl groups. (c) Binding can also be enhanced by changing the phase state of the lipid bilayer from liquid to solid (i.e. going from EL to DPPC) or by increasing the size of the liposomes (i.e. going from 60–80 to 300 nm). By far the most promising systems, from the point of view of constructing polyelectrolyte multilayers on liposome cores without disruption of liposome integrity, involve small, liquid, anionic liposomes coated initially with polycations carrying pendant alkyl groups.
Keywords: Polycation; Polyanion; Liposome; Adsorption; Multilayer;
Classification and evaluation of microfluidic devices for continuous suspension fractionation by T. Kulrattanarak; R.G.M van der Sman; C.G.P.H. Schroën; R.M. Boom (53-66).
Membrane processes are well-known for separating and fractionating suspensions in many industries, but suffer from particle accumulation on the membrane surface. Currently, there are new developments using microfluidic devices for cell/DNA sorting and fractionation. We anticipate these devices are also applicable to fractionation of polydisperse and concentrated suspensions (e.g. foods), and may potentially have fewer problems with particle accumulation compared to membranes. This review article presents an overview of relevant microfluidic devices. We focus on their performance with respect to concentrated suspensions, as one finds in food industry. We give quantitative estimates on their yield, selectivity, and the potential for large-scale application. From this evaluation follows that deterministic ratchets seem most promising.
Keywords: Deterministic ratchet; Fractionation; Membrane separation; Microfluidic device; Suspension;
Initial stages of SBA-15 synthesis: An overview by Vladimir L. Zholobenko; Andrei Y. Khodakov; Marianne Impéror-Clerc; Dominique Durand; Isabelle Grillo (67-74).
This work presents an overview of the data obtained for SBA-15 synthesis under the reaction conditions using synchrotron based small angle X-ray scattering and small angle neutron scattering. Three major stages in the synthesis of SBA-15 materials proceeding according to the cooperative self-assembly mechanism have been identified, and the structures of the intermediates species have been established. Our in situ time-resolved neutron scattering experiments demonstrate that only spherical micelles of the templating agent are present in the synthesis mixture during the first stage of the reaction. According to the neutron scattering and X-ray scattering data, in the second stage of the reaction the formation of hybrid organic–inorganic micelles is accompanied with the transformation from spherical to cylindrical micelles, which takes place before the precipitation of the ordered SBA-15 phase. During the third stage, these micelles aggregate into a two-dimensional hexagonal structure, confirming that the precipitation takes place as the result of self-assembly of the hybrid cylindrical micelles. As the synthesis proceeds, the voids between the cylinders are filled with the silicate species which undergo condensation reactions resulting in cross-linking and covalent bonding, leading to the formation of highly ordered SBA-15 mesostructure. This work demonstrates that valuable structural information can be obtained from X-ray and neutron scattering characterisation of complex systems containing periodic phases with d-spacing values up to 30 nm, and that both techniques are powerful means for in situ monitoring of the formation of nanostructured materials.
Keywords: In situ SAXS; In situ SANS; SBA-15 synthesis; Self-assembly; Nanomaterials;