Colloidal silica interaction between

A detailed study by Grieser and co-workers [169] of the forces between a gold-coated colloidal silica sphere and a gold surface reveals the preferential adsorption of citrate ions over chloride to alter the electrostatic interaction. 

It is difficult to obtain meaningful results on colloidal interactions unless the samples have low polydispersity. Studies of colloidal interactions between whole casein micelles can be affected by the polydispersity of native casein micelles. (Stothart,1987b). To circumvent the problem of polydispersity, the food system can be deposited on monodisperse silica spheres (Rouw and de Kruif,1989). 

Adsorption of block copolymers onto a surface is another pathway for surface functionalization. Block copolymers in solution of selective solvent afford the possibility to both self-assemble and adsorb onto a surface. The adsorption behavior is governed mostly by the interaction between the polymers and the solvent, but also by the size and the conformation of the polymer chains and by the interfacial contact energy of the polymer chains with the substrate [115-119], Indeed, in a selective solvent, one of the blocks is in a good solvent it swells and does not adsorb to the surface while the other block, which is in a poor solvent, will adsorb strongly to the surface to minimize its contact with the solvent. There have been a considerable number of studies dedicated to the adsorption of block copolymers to flat or curved surfaces, including adsorption of poly(/cr/-butylstyrcnc)-ft/od -sodium poly(styrenesulfonate) onto silica surfaces [120], polystyrene-Woc -poly(acrylic acid) onto weak polyelectrolyte multilayer surfaces [121], polyethylene-Wocfc-poly(ethylene oxide) on alkanethiol-patterned gold surfaces [122], or poly(ethylene oxide)-Woc -poly(lactide) onto colloidal polystyrene particles [123],... 

The work of Larson et al. (62) represented the first detailed study to show agreement between AFM-derived diffuse layer potentials and ((-potentials obtained from traditional electrokinetic techniques. The AFM experimental data was satisfactorily fitted to the theory of McCormack et al. (46). The fitting parameters used, silica and alumina zeta-potentials, were independently determined for the same surfaces used in the AFM study using electrophoretic and streaming-potential measurements, respectively. This same system was later used by another research group (63). Hartley and coworkers 63 also compared dissimilar surface interactions with electrokinetic measurements, namely between a silica probe interacting with a polylysine coated mica flat (see Section III.B.). It is also possible to conduct measurements between a colloid probe and a metal or semiconductor surface whose electrochemical properties are controlled by the experimenter 164-66). In Ref. 64 Raiteri et al. studied the interactions between... 

The purpose of this study was to explore the interaction between slurry particles and wafer surfaces by the measurements of their zeta potentials. The zeta potentials of slurry particles such as fumed and colloidal silica, alumina, ceria and MnOj and substrates such as silicon, TEGS, W, and A1 have been measured by electrophoretic and electroosmosis method to evaluate the electrical properties of surfaces, respectively. The zeta potential of oxide and metal surfaces showed similar values to those of particles as a function of pH. The interaction energy between alumina and silica particles and TEOS, W and A1 substrate were calculated based on DLVO theory. No deposition of silica particles on TEOS and the heavy deposition of alumina particles on metal substrates were observed in the particle deposition test. Experimental results were well agreed with the theoretical calculation. 

Figure 3. DLVO total interaction energy between TEOS surface and (a) colloidal silica and (b) alumina particles at pH 11.

Physical interactions between drug and excipient also can compromise quality. Adsorption of drug by microcrystalline cellulose resulted in drug dissolution being less than complete. Interaction between chloramphenicol stearate and colloidal silica during grinding led to polymorphic transformation. 

Chemical investigations of this biological system have attempted to address the following questions (1) What is the microstructure of the hydrated Si02 within costal rods (2) How are the costal rods linked together in the intact basket (3) What is the nature of the surface silica in the costal rods These questions were answered in some part by studies of intact and partially intact loricae, on demineralized costae, and by considering the nature of the interaction between metal ions (Fe, Co +), colloidal silica, and liposomes with the costal strips. 

The influence of the cations and anions has been discussed separately with the solution properties and reactions in the main focus. It has, however, been known over 100 years that anions play a crucial role for the stabilization and coagulation of colloids. More recently, the contribution of anions on the stabilization of particles, biocolloids, and bubbles has received renewed attention. - In these papers, it has been pointed out that there exists a collaborative interaction between cations and anions upon adsorption of one of the complexes from solution. At high concentrations this effect renders the simple indifferent ions specific and selective to each other. It is also seen as a dependency on the acid-base pair chosen for the regulation of the pH. This effect certainly needs to be added as an extension to (correction of) the DLVO theory. However, as shown in this paper, it is just as probable that the anion and cation collaborate during the adsorption and formation of gels and precipitates at the surface. The presence of such mixed phases has been confirmed experimentally, e.g., during the formation of hydroxoapatite in silica gel layers. ... 

With the increased level of understanding of the cyclization dynamics as monitored by intramolecular excimer fluorescence, it is now possible to extend this probe to the study of systems more complex than dilute solutions. One such situation involves the structure and dynamics of macromolecular complexes formed between polymeric proton donors and acceptors in aqueous solution. For example, there has been widespread interest in the complexes formed between poly(ethylene glycol) and poly(acrylic acid) or poly(methacrylic acid) in aqueous solution (34, 35). A second, complicated morphological problem is to describe the configurational behavior of polymer chains adsorbed on colloidal particles. This research has relevance to the understanding of steric stabilization. One system of particular interest is the interaction of poly(ethylene glycol) and colloidal silica (36-40). 

Moaddeb and Koros (1997) described the deposition of silica on polymeric MF membranes as non-uniform. This means that cake characterisation is difficult as a cracks could vary the results. Meagher et al (1996) stated that attractive interaction between membranes and particles would cause a flux decline, even if the particles were aggregated. Aggregation reduced the flux decline if there was no attraction between the membranes and colloids. The authors outlined the restrictions of the gel polarisation model, as the porosity of the deposit is not accounted for in the model. It was also suggested that the resistance of the gel layer is more important than the particle-surface interaction (what is often referred to as adsorption). 

Preparation of ultrafine monodisperse hybride particles, dispersible in low polar organic solvent, from monodisperse colloidal silica by two-step polymer modification was studied. Bindings of the secondary polymer to monodisperse poly(maleic anhydride-styrene)-modified colloidal silica particles (120 nm) have made the composites in low polar solvent dispersible. The dispersion of the particles in good solvent for the secondary polymer is due to the steric repulsion of solvated polymer chains. The dispersibility of the hybrid particles in poor solvent-rich solution was controlled by delicate balance between nonpolar-nonpolar interaction and electrostatic repusion among the particles. 

In this section we present a brief account of the most recently published smdies and techniques concerning the solid-liquid interface involving silica and related materials. Interactions between solutions and solid surfaces play an important role in several processes such as ore flotation, colloidal stabilization, oil recovery, soil pollution and so on [105]. 

Percy and coworkers [39,40] synthesized colloidal dispersions of polymer-silica nanocomposite particles by homopolymerizing 4-vinylpyridine or copolymerizing 4-vinylpyridine with either methyl methacrylate, styrene, n-butyl acrylate or n-butyl methacrylate in the presence of fine-particle silica sols using a free-radical in aqueous media at 60°C. No surfactants were used and a strong acid-based interaction was assumed to be a prerequisite for nanocomposite formation. The nanocomposite particles had comparatively narrow size distributions with mean particle diameters of 150-250 nm and silica contents between 8 and 54 wt.%. The colloidal dispersions were stable at solids contents above 20 wt.%. 

---