Poly gels structures

Sodium Poly(4-styrene sulfonate). The sol—gel processing of TMOS in the presence of sodium poly-4-styrene sulfonate (NaPSS) has been used to synthesize inorganic—organic amorphous complexes (61). These sodium silicate materials were then isothermally crystallized. The processing pH, with respect to the isoelectric point of amorphous silica, was shown to influence the morphology of the initial gel structures. Using x-ray diffraction, the crystallization temperatures were monitored and were found to depend on these initial microstructures. This was explained in terms of the electrostatic interaction between the evolving silicate structures and the NaPSS prior to heat treatment at elevated temperatures. 

Poly(vinyl methyl ether), PVME, is a thermo-sensitive polymer. The aqueous solution has a Lower Critical Solution Temperature (LCST) of 37 °C. Therefore, PVME is soluble in water below its LCST, but insoluble above its LCST. When an aqueous solution of PVME is irradiated with y-rays the solution becomes PVME hydrogel [18, 19]. The gel shows thermo-sensitivity similar to the solution, and swells below 37 °C and shrinks above this temperature. It is important to form a fine porous gel structure to obtain quick response gels. There are two methods for the purpose. One is a method using micro-phase separation by heating. The other is a method using micro-phase separation by blending of polymer solutions. 

Dispersants are polyanionic polymers, mostly poly(naphthalene sulfonate) (PNS) and poly melamine sulfonate, which adsorb on the positively charged zones of the particle surfaces and suppress the interactions required to build the gel structure. Thus, the slurry is dispersed (Figure 17). With large quantities of dispersant, it is possible to obtain a New-... 

Work on poly(ethylene oxide) gels indicates that the presence of solvents such as chloroform and carbon disulfide contributes to the formation of a uniform helical conformation. The gelation behavior and the gel structure depend on the solvent type which, in turn, is determined by solvent-polymer interaction. In a good solvent, polythiophene molecules exist in coiled conformation. In a poor solvent, the molecules form aggregates dnough die short substituents. ... 

SILICA GELS, AEROGELS, SILOCHROME, AND POLY(METHYLSILOXANE) STRUCTURAL, INTERFACIAL AND ADSORPTION CHARACTERISTICS,... 

As discussed before, addition of free non-adsorbing polymer can produce weak flocculation above a critical volume fraction of the free polymer, This weak flocculation produces a gel structure that reduces sedimentation. As an illustration, results were obtained for a sterically stabilised suspension [using a graft copolymer of poly(methyl methacrylate) with poly(ethylene oxide) side chains] to which hydroxyethyl cellulose with various molecular weights was added to the suspension. The weak flocculation was studied using oscillatory measurements. Figure 7.52 shows the variation of the complex modulus G with p. 

The sol-gel process starts with a solution of metal oxides (usually metal-alkoxy compounds such as tetraorthoethylsilicate (TEOS) are used) that undergo hydrolysis and poly-condensation to form a rigid matrix of cross linked metal-oxide network followed by thermal evaporation to form a matrix with interconnecting pores. The sensing agents are added during the process of condensation and are encapsulated into the gel structure formed around them. 

All SCL basically consist of hydrophilic polymers that maintain then-gel structure, with the ability to swell and not dissolve by intermolecular crosslinking. Therefore, natural polymers, such as agarose and gelatin, are potential candidates for its material. However, currently commercially available SCL are made only of copolymers of methacrylic acid derivatives, mainly PHEMA, and several other monomers because of stability and safety concerns. Lenses with a water content of 30-40 % are made mostly of PHEMA and those with water contents of70-80 % are made of copolymers ofN-vinyl pyrrolidone (NVP), acrylamide (AAm), HEMA, and methacrylic acid (MA). There are also poly(vinyl alcohol) derivatives. Table 2 shows the names and chemical structures of various SCL components [6]. 

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