Colloidal silica surface modification

Modifications of monodisperse colloidal silica, of 10 or 500 nm in diameter, were carried out using trialkoxysilane-terminated polymer in a low polar solvent, such as acetone or 1,2-dimethoxyethane. without coagulation during the coupling reaction (35,37-42). In this modification, the hydrophobic polymer can be efficiently bound to hydrophilic colloidal silica surface. The reaction mechanism of the binding... 

The -potential of colloidal silica surface treated by acrylate copolymers is affected by pH. The -potential of untreated colloidal silica at a pH of 4 is -7 mV and it decreases to -32 mV at a pH of 7. Modification of the surface of colloidal silica changes its surface properties and behavior. In another study on filler modification, hydroxyapatite was modified for medical applications with several differ-... 

Figure 11.14 Sol-gel synthesis of colloidal silica spheres, modification of surface with methacrylate groups, and copolymerization with methyl acrylate to form a CCA of silica particles in a polyfmethyl acrylate) film. DMPA, 2,2-dimethoxy-2-phenylacetonephenone. (Reproduced with permission from J. M. Jethmalani and W. T. Ford, Chem. Mater. 1996, 8, 2138.)...

Keywords Clays Emulsion polymerization Iron oxide Metals Organic/ inorganic composite colloids Particle morphology Pigments Quantum dots Silica Surface modification... 

A spiropyran moiety that undergoes a reversible transformation from the neutral form to the charged merocyanine form and back upon irradiation with UV and visible light, respectively (Scheme 8.2) [37] appeared to be suitable for controlling the ionic permselectivity of a colloidal membrane by light. The succinimidyl ester derivative [38] of the spiropyran was prepared and used to treat the amine-modified colloidal films assembled on a Pt electrode (Scheme 8.3) [39]. The successful silica surface modification with spiropyran moieties was confirmed using UV spectroscopy. 

The Stober method can be used to form core-shell silica nanoparticles when a presynthesized core is suspended in a water-alcohol mixture. The core can be a silica nanoparticle or other types of nanomaterials [46, 47]. If the core is a silica nanoparticle, before adding silicon alkoxide precursors, the hydroxysilicates hydrolyzed from precursors condense by the hydroxide groups on the surface of the silica cores to form additional layers. If the core is a colloid, surface modification of the core might be necessary. For example, a gold colloid core was modified by poly (vinylpyrrolidone) prior to a silica layer coating [46]. 

Solid surfaces nature of the surface of colloidal silica, clays, zeolites, silica gels, porous Vycor glasses, alumina rigidity, polarity and modification of surfaces... 

Sutra, P., Fajula, F., Brunei, D., Lentz, P., Daelen, G. and Nagy, J. B. Si-29 and C-13 MAS-NMR characterization of surface modification of micelle-templated silicas during the grafting of organic moieties and end-capping, Colloids Surf., A, 1999, 158, 21-27. 

Dispersion stabilization with nanoparticles is also known. A recent example of a dispersion stabilized by nanoparticles was published by Tohver et al. This group used zirconia particles to stabilize an aqueous colloidal system of larger silica particles. The dispersion was stabilized by electrostatic stabilization and thus is essentially applicable only to aqueous systems. Surface modification of the particles changes the stabilization mechanism to steric stabilization, and dispersions in both aqueous and nonaqueous systems have been demonstrated. 

Pham, K.N., Fullston D., and Sagoe-Crentsil, K., Surface modification for stability of nano-sized silica colloids, J. Colloid Interf. Sci., 315, 123, 2007. 

Jesionowski, T, Influence of aminosilane surface modification and dyes adsorption on zeta potential of spherical silica particles formed in emulsion system. Colloids Surf. A, 222, 87, 2003. 

Research of Soviet scientists is surveyed. Contributions to various aspects of the colloid chemistry of silica are examined preparation and stabilization of silica hydrosols preparation of silica gels structural characterization of silicas surface chemistry elucidation adsorption and ion-exchange property examination and geometric and chemical modification of silicas, silica coatings, and so forth. 

Perhaps the simplest use of colloidal silica in this area is its use to firictionize and coat the film base material to both make it easier to be conveyed through the process and also to prevent it from blocking or adhering to itself when rolled up. The use of colloidal silica as an anti-blocking agent is discussed above under the Surface Modification of plastic films. 

First of aU, silica coating provides very effective protection against flocculation, which is a fundamental requirement when concentrated dispersions are to be prepared. The characteristic properties of silica surfaces provide enhanced stability in aqueous dispersions, and allow for more elaborate surface modifications which can ultimately lead to the preparation of colloids readily dispersed in a wide range of organic solvents. 

To create particles with a hydrophobic core and a hydrophilic shell, preformed hydrophobic polymer particles can be used as substrate for the covalent grafting of hydrophilic polymer chains. Aqueous emulsion polymerization is thus the method of choice for synthesis of core particles with submicrometric diameter (due to the scope of this review article, discussion will be restricted to aqueous emulsion polymerization, although some examples of particle substrates created via suspension polymerization exist however, with much larger diameters). The grafting methods are very close to those used for the surface modification of inorganic materials, such as for instance silicon wafers or colloidal silica particles [46,48-52], Various strategies can be employed such as ... 

Sun Y, Zhang Z, Wong CP. Study on mono-dispersed nano-size silica by surface modification for underfill applications. J Colloid Interface Sci 2005 292 436 44. 

Silica colloidal crystals with reversible permselectivity controlled by the presence of a small molecule can be prepared by surface modification of the nanopores with a responsive DNA aptamer [69]. Aptamer oligonucleotides exhibiting selective and specific binding properties toward molecules [70] have been developed for uses in medicine, analytical chemistry, and materials science [71,72], These aptamers may provide the ability to control the molecular transport through a nanoporous colloidal film by utilizing conformational changes in a biopolymer in response to small molecule binding. 

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