Silica particles surface modification

Comparing PDMS/HMDS- and HMDS-modified silica particles, a lower phase shift of up to 70° has been observed for the PDMS/HMDS silicas, and for the HMDS silicas a higher phase shift of up to 90° has been found. Differences in phase shift values indicate the impact of surface modification on the local hardness of the silica particles. PDMS modification leads to a softer, polymer-like grafting, whereas pure HMDS modification oidy increases the hydrophobicity by a hard monolayer formation of trimethylsiloxy groups. HMDS-treated silicas seemed to show a weaker interaction with the toner resin surfaces. In contrast, PDMS/HMDS-treated silicas show stronger adhesion to the toner resin surfeces, so they can easily be imaged at high resolution. 

Modification of Porous Silica Particle Surfaces with Poly(Acrylic Acid)... 

The present study is concerned with the modification of functional polymers onto porous silica particle surfaces. Our primary interest is to improve particle surface characteristics. Poly(acrylic acid) was chosen as the functional polymer to provide pH-intelligent, surface-responsive particles. The PAA chains under acid conditions are usually coiled, while under basic conditions the chains are extended due to electrostatic repulsion of the carboxylate ions. By controlling the pH, the surface characteristics can be tailored to respond to specific pH environments. Pore size distribution and specific surface area of modified silica are calculated from the amount of nitrogen adsorbed on the surface. The water penetration rate and porosity for different pH were measured for estimation of the surface properties ... 

The use of silica particles in bioapplications began with the publication by Stober et al. in 1968 on the preparation of monodisperse nanoparticles and microparticles from a silica alkoxide monomer (e.g., tetraethyl orthosilicate or TEOS). Subsequently, in the 1970s, silane modification techniques provided silica surface treatments that eliminated the nonspecific binding potential of raw silica for biomolecules (Regnier and Noel, 1976). Derivatization of silica with hydrophilic, hydroxylic silane compounds thoroughly passivated the surface and made possible the use of both porous and nonporous silica particles in all areas of bioapplications (Schiel et al., 2006). 

Surface functionalization of silica particles or fluorescent silica particles typically is done using functional alkyl silanes. The process may be used to add a reactive group to the surface of the particles for spontaneous coupling to biomolecules or it may be used to add the appropriate nucleophilic group to the surface, such as an amine or a carboxylate. Silane modification chemistry is discussed in more detail in Chapter 13. 

Figure 13.23a shows the first mechanism, which is mainly chemical in nature. The silica removal rate is accelerated by the ceria-silica interactions, which results in the improved dissolution of the silica substrate during polishing. Figure 13.23b shows the second mechanism, which is based on physicochemical particle-surface interactions in which the ceria-silica bonding does not result in direct modification of the silica substrate but enhances the... 

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