Polymer stabilisers for temperature-induced dispersion gelation: versatility and control

In this study the temperature-induced gelation of butadiene-acrylonitrile latex containing the added temperature-responsive polymer surfactant, poly(NIPAM-co-PEGMa) is investigated for the first time. (NIPAM and PEGMa are N-isopropylacrylamide and poly(ethylene glycol)methacrylate, respectively.) The results are compared with temperature-induced gelation of oil-in-water emulsions containing 1-bromohexadecane. The effect of added anionic surfactant, NaDBS (sodium dodecylbenzene sulfonate) on the temperature-induced gelation process and mechanism is considered. It was found that the gelation temperature (T(gel)) for the latex occurs at the cloud point temperature (T(cpt)) of the polymer and that T(gel) is much less affected by added NaDBS than is the case for emulsion gelation. The mathematical predictive theory recently derived for temperature-induced emulsion gelation was applied to the latex data and gave a good fit (i.e., T(gel) approximately 1/C(p), where C(p) is the concentration of added poly(NIPAM-co-PEGMa)). However, the causes for the variation of T(gel) with C(p) for temperature-induced latex and emulsion gelation are different. The variation of T(gel) for latex gelation in the presence of added NaDBS originates from surfactant association with poly(NIPAM-co-PEGMa) which increased T(cpt). In the case of emulsion gelation there are electrostatic interactions above T(cpt) which control T(gel). The subtle difference in the temperature-induced latex gelation mechanism is a consequence of the very high latex surface area (cf. emulsion), small inter-particle separation and the presence of electrolyte. The reason that T(gel) follows 1/C(p) for the latex is due to a fortuitous T(cpt) approximately 1/C(p) relationship that applies for poly(NIPAM-co-PEGMa) solution in the presence of NaDBS. The work presented here shows that addition of poly(NIPAM-co-PEGMa) to dispersions gives a versatile method for temperature-triggered gelation. Furthermore, the theory presented provides a framework for predicting their gelation temperatures.