Solvent effects on the kinetics of gelation and the crosslink density of polysiloxane gels

Abstract

A wide range of hydrocarbons were rapidly gelled by adding a polysiloxane copolymer in the presence of divinylbenzene and a platinum catalyst. The gel point was measured over a range of concentrations for hydrocarbons/solvents and organogels, using three separate methods: rheology, visual (tilt-tube) and FTIR. As the fraction of solvent was increased, the rate of reaction decreased, leading to an increase in the gelation time. The absolute value of the gel point depends upon the techniques used to measure it. For any particular system the gel point values always followed the order: rheology > visual > FTIR. The crosslink densities of the gel systems were determined using both swelling and thermomechanical analysis. The swelling measurements confirmed that the addition of large quantities of solvent markedly reduced the crosslink density of the obtained chemical gel networks, which helped in designing gels with suitable critical strength for effective field work. Also the effectiveness of gelation with the proposed gelling system for different hydrocarbons/solvents was evaluated, and discussed in relation to their dielectric properties.

Benzene physical and chemical organogels: Effect of network scaffolding on the thermodynamic behavior of entrapped solvent molecules

“…Generally, critical parameters controlling the gelation using chemical organogelators are: quantity of gelator and cross‐linker, temperature of the reaction, quality of hydrocarbon/solvent, and type of catalyst used. The in situ reaction and gelation was monitored by evaluation of the gel point by FTIR, low oscillation rheology, and measurements of cross‐link density of the so‐obtained gel networks and discussed elsewhere 48…”

Mechanism of solvent entrapment within the network scaffolding in organogels: thermodynamic and kinetic investigations

“…To initiate the crosslinking reaction, catalysts were necessary and a Pt‐complex was found to be the most effective. The reaction of cross‐linking of polymer ‘A’ with DVB was initiated by addition of a Pt‐complex as presented in Scheme 42, 43…”

“…Generally, the critical parameters controlling the gelation of chemical organogels are: quantity of gelator and crosslinker, temperature of reaction, quality of solvent and type of catalyst used. This in situ reaction and gelation was monitored through the evaluation of the gel point by FTIR, low‐oscillation rheology and measurement of crosslink density of the resulting gel network by the authors and has been discussed elsewhere 43…”

Rheological assessment of the sol–gel transition for self-assembling low molecular weight gelators

“…However, random errors associated with the stochastic nature of self assembly cannot be avoided. Typically, in the literature the gel point is determined using the cross over point between G′ and G″ or tan δ =1 (Markovic, Dutta, Williams, & Matisons, 2003;Matejka, 1991;Mezger, 2006). Similarly, in other instances the gel point has been monitored with the inflection point of either the G′ curve using oscillatory rheology or the "infinite viscosity" using flow rheology (Liang, Cook, Sautereau, & Tcharkhtchi, 2009).…”