Polyvinyl alcohol, surface conditioning

The rubber particle size in the final product increases several fold if the prepolymerization is carried out in the presence of a dilute aqueous solution of an alkane sulfonate or polyvinyl alcohol in place of pure water. The addition of a surface-active agent converts the coarsely dispersed oil-water mixture—obtained as above in the presence of pure water—into an oil-in-water emulsion. In this case even prolonged stirring during prepolymerization does not decrease the rubber particle size appreciably in the final product. The stabilization of the droplets of the organic phase in water by the emulsifier obviously impedes or prevents agitation within the polymeric phase. Figure 1 shows the influence of these three prepolymerization methods (under otherwise equal reaction conditions) on the dispersion of rubber particles in polystyrene. 

For instance, Yadav and Ahuja prepared nanoparticles using gum cordia as the polymer and to evaluate them for ophthalmic delivery of fluconazole. A w/o/w emulsion containing fluconazole and gum cordia in aqueous phase, methylene chloride as the oily phase, and dioctyl sodium sulfosuccinate and polyvinyl alcohol as the primary and secondary emulsifiers, respectively, were cross-linked by the ionic gelation technique to produce a fluconazole-loaded nanoreservoir system. The formulation of nanoparticles was optimized using response surface methodology. Multiple response simultaneous optimizations using the desirability approach were used to find optimal experimental conditions. The optimal conditions were found to be concentrations of gum cordia (0.85%, w/v), di-octyl sodium sulfosuccinate (9.07%, w/v), and fluconazole (6.06%, w/v). On comparison of the optimized nanosuspension formulation with commercial formulation, it was found to provide comparable in vitro corneal permeability of... 

The preparation conditions determine the special properties of silica gel. Physicochemical properties such as hardness and polarity of silica gel are related to particle size (fim), size distribution, shape, surface area (mVg), pore system [size (A) and distribution], and presence or absence of additives—that is, binders, contaminants, or indicators. The surfaee area of silica gel adsorbent for TLC is typically 300 ta600 m /g, pore volume is —0.75 ml/g, and pore diameters range from 40 to 80 A (most often 60 A or 6 nm). Adsorbent with larger surface area (smaller particle size) will generally give better resolution but a slower development time. The usual binder for commercial TLC adsorbent powders is 5-20% gypsum (silica gel G). Precoated plates usually have organic binders such as polyesters or polyvinyl alcohol. 

These microspheres are precisely calibrated, spherical, hydrophilic, microporous beads made of tris-acryl co-polymer coated with gelatin. They come in defined range of sizes, ranging from 40 to 1200 pm in diameter. Their smooth hydrophilic surface, deformability and minimal aggregation tendency have been shown to result in a lower rate of catheter occlusion and more distal penetration into the small vessels [32]. Their efficacy has been evaluated in several conditions, and vdien compared to the standard polyvinyl alcohol particles (PVA) particles, a deeper penetration and embolization of smaller and more peripheral vessels may be achieved. This distal embolization may limit the development of any collateral blood supply. Also, in a study where PVA particles and tris-acryl microspheres of similar size were compared, the level of vascular occlusion with calibrated tris-acryl microspheres precisely correlated with particle size whereas the level of vascular occlusion with PVA particles did not. Another study has demonstrated that in embolized tumors. 

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