Gelation effect

Torkelson and coworkers [274,275] have developed kinetic models to describe the formation of gels in free-radical pol5nnerization. They have incorporated diffusion limitations into the kinetic coefficient for radical termination and have compared their simulations to experimental results on methyl methacrylate polymerization. A basic kinetic model with initiation, propagation, and termination steps, including the diffusion hmitations, was found to describe the gelation effect, or time for gel formation, of several samples sets of experimental data. 

The OH group of organic acid is characterised by an absorption band at 3400 cm 1, corresponding to the stretching vibration. The best heat stability and gelation effects are obtained with ESO for long heating times, which are confirmed by dehydrochlorination rate constants. 

The electroviscous effect can influence the results of viscosity determinations, but this can be avoided by using a sufficiently high concentration of salt12 when linear specific viscosity concentration versus concentration curves are obtained. Gelation effects with Fe++, Fe+++ and Cu++ ions also occur127 and so should be avoided. 

Thus, with a knowledge of the effects of gelation and an accurate chemoviscosity model, the optimum flow and cure conditions can be established. The measurement techniques for chemoviscosity and gelation effects will be reviewed next. 

The gelation effect treated as formation of a cluster, subtending the system, resnlts to essential changes of parameters describing this system, in a gelation point [26]. So, the clnsters diffusion rate (macromolecular coils rate) with mass m... 

V. Ethylhydroxyethylcellulose. EHEC (39) is included here even though it has limited applications in personal care. The interest in EHEC stems from its ability to gel at temperatures only slightly above 30°C, particularly in the presence of anionic and cationic surfactants (167-169). The hydrophobic domains on EHEC build strong interpolysaccharide cross-links as the polysaccharide solution is warmed. This thermal gelation effect is sensitive to the concentrations of the EHEC and surfactant employed (169). The lipophilic nature of the ether substituents on EHEC all but qualify it as a hydrophobically modified HEC (Section III.E.). 

The gelation effect can be completely prevented without causing any ill effect to the reaction if the process is carried out in the presence of p-phenylene-diamine derivatives or imidazole [183-185]. 

Mainly due to solvent evaporation and surface tension, the solution front is always directed toward the center of the liquid film. At the first stage of evaporation the solution front recedes smoothly then after a short while it starts receding intermittently, with jump. The jumping instability with a stick and slip motion of the receding front is ascribable to the local gelation effect of a polymer at the three-phase line (liquid-substrate-air boundary) where polymer concentration is assumed to be higher than the bulk polymer solution. The local gelation prevents... 

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