Anion and solvent responsive copolymeric gels - Morphology, annealing, and surfactant stimuli

The phase diagram of the pseudo-ternary aqueous 1-propanol (50:50 H2O:1-propanol by weight), ionic liquid acrylate, 1-(11-acryloyloxyundecyl)-3-methyl imidazolium tetrafluorborate (ILBF4), and methyl methacrylate (MMA) system is mapped for weight fractions of ILBF4 less than 0.75 at 25 °C and at 60 °C. The mapped region is composed of a very large single-phase microemulsion domain and an appreciable multi-phase (emulsion) domain. This emulsion domain shrinks in size with increasing temperature, in contrast to the homologous bromide system (ILBr) with an emulsion domain that is insensitive to temperature. Microemulsion polymerization of the 0.70/0.15/0.15 composition in this solvent/ILBF4/MMA system produces a solvogel that is further examined for its solvent and anion stimuli responsiveness. Aqueous-DMSO solvent exchange of the PF6− exchanged materials shows nearly reversible, but dissipative behavior on a macro-scale. Transformation of transparent gel to open cell porous material by anion exchange with PF6− is found to exhibit a (third) long time-scale behavior, wherein anion exchange is limited by ionic diffusion through condensed polymeric chains. The accompanying spinodal decomposition is also demonstrated to be driven by an amphiphilic anion, bis(2-ethylhexyl)sulfosuccinate, with interesting material effects to produce more pliable porous material than obtained by exchange with PF6−. Thermal and solvent annealing treatments show that these porous materials can be activated to lower their internal specific surface area, while retaining free volume available for stimuli-induced poration.

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