Interaction of ionic liquid-dissolved polymers
Ionic liquids (ILs), neoteric salts with Tm < 100°C, have garnered vast interest due to a number of unique properties including vanishingly low volatility, non-toxicity and property tunability. Many polymers were found to dissolve in ILs, and polymer solution properties were measured using the room temperature IL 1-ethyl-3-methylimidiazolium ethylsulfate, [EMIM][EtSO 4], as a model IL. Polyethylene glycol (PEG) dissolves in [EMIM][EtSO 4] above ∼60°C, the neat polymer's melting temperature, and if concentration and molecular weight are high enough, the solution transforms into a semi-transparent gel at lower temperature. Thermoreversible gelation is traced to kinetically frustrated polymer crystallization, a mechanism established previously for many pairings of crystallizable polymer with aqueous or organic solvent. Negatively and positively charged polymers dissolve in [EMIM][EtSO 4], typically over long time periods, and solution chain properties are measured using common physiochemical techniques. Electrostatic interactions of sodium poly(styrene sulfonate) are screened without the need of added salt due to the presence of the charged solvent and size-molecular weight relationships indicate sodium poly(styrene sulfonate) assumes a coiled conformation in solution. Lysozyme dissolves in [EMIM][EtSO4] assuming an expanded conformation with compromised secondary structure, the unfolded structure stabilized by the IL. Preferential solvation of dissolved lysozyme in mixed [EMIM][EtSO 4]/H2O solvents prevents lysozyme aggregation above its denaturation temperature.