Spinodal Decomposition of a Polymer and Ionic Liquid Mixture: Effects of Electrostatic Interactions and Hydrogen Bonds on Phase Instability

2016-01-26T00:00:00Z (GMT) by Issei Nakamura
We studied the spinodal decomposition of a homopolymer and ionic liquid mixture. Our theory accounts for the dielectric contrast and hydrogen bond between the polymer and the ionic liquid and the effect of fluctuations in the local density and electrostatic potential. We attempted to rationalize the observed shift in the critical point and the asymmetry of the observed spinodal curve by applying the self-consistent field theory and Langmuir adsorption model. The dielectric contrast between the polymer and the ionic liquid produces a shift in the critical point toward polymer-rich regions. The fluctuation effect yields drastic changes in the trend of the phase boundary. We show that both effects are marked by the appearance of inflection points in the spinodal curve. Although hydrogen bonding also yields similar effects, the spinodal curve rather exhibits a double-well structure or relatively flat structure when combined with the solvation energy of ions. Hydrogen bonding, ion solvation, and the fluctuation have equal significance on the magnitude and trend of the spinodal curve. Our theory provides strategies to dissolve low-dielectric polymers in ionic liquids by altering the dielectric constant of ionic liquids and employing hydrogen bonding.