Synthesis and Temperature-Induced Phase Transfer Behavior of Thermosensitive Hairy Particles between Aqueous Solution and a Hydrophobic Ionic Liquid

This dissertation presents the synthesis of a family of thermosensitive polymer brush-grafted silica particles and the study of their thermally induced phase transfer behavior between water and a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMIM][TFSA]). The hairy particles were prepared by surface-initiated atom transfer radical polymerization.

Chapter 1 describes the synthesis and phase transfer behavior of a series of 205 nm silica particles grafted with thermosensitive polymers of methoxyoligo(ethylene glycol) methacrylates. The hairy particles with sufficiently high lower critical solution temperatures underwent reversible and quantitative transfer between water and [EMIM][TFSA] in response to temperature changes. The transfer temperature (T_tr) of hairy particles from water to [EMIM][TFSA] upon heating was a linear function of the cloud point (CP) of corresponding free polymer in [EMIM][TFSA]-saturated water. Chapter 2 presents the synthesis and study of thermo- and pH-sensitive hairy particles. A small amount of carboxylic acid groups was incorporated into the thermosensitive polymer brushes. The T_tr of hairy particles from water to [EMIM][TFSA] increased with increasing the pH of the aqueous phase. By exploiting the tunability of T_tr, we demonstrated pH-driven reversible transfer of hairy particles at a constant temperature and multiple transfer processes by controlling both temperature and pH. Chapter 3 describes a study of the effect of silica core size on phase transfer of thermosensitive hairy particles. The transfer temperatures of thermosensitive polymer brush-grafted 67 nm nanoparticles were higher by 1-3 °C than those of thermosensitive hairy particles with silica core sizes of ~ 200 nm. They also moved faster by 1.8 times from water to [EMIM][TFSA] than larger hairy particles.

Chapter 4 presents the synthesis of a series of mixed poly(tert-butyl acrylate) (PtBA)/polystyrene (PS) brushes from Y-initiator-functionalized 67 nm silica nanoparticles. Transmission electron microscopy studies showed that with the increase of PS M_n from below to above that of PtBA, the morphology of mixed brushes evolved from isolated PS nanodomains, to truncated wedge-shaped nanostructures, and two-layered structures. A notable feature of the morphology of mixed brushes on 67 nm nanoparticles is the truncated wedge-shaped nanostructures. A summary of this dissertation research and future work are provided in Chapter 5.