Rearrangement of Nanoporous Cavity Structures in Crystalline Syndiotactic Polystyrene Associated with Stress-Induced Phase Transition.

Abstract

This work demonstrates the possibility of rearranging nanoporous cavity structures in crystalline syndiotactic polystyrene (s-PS) by applying external stresses. A molecular dynamics (MD) simulation was performed for the s-PS crystal with increasing or decreasing of each stress tensor component, starting from the nanoporous ε form. Upon uniaxial compression along the b-axis, the ε form was transformed into a lower density porous form, accompanied by significant elongation of the a-axis. The new form, named the S-I form, was stable only under the stress and was transformed into the γ form after release of the stress. The cavity structure was drastically changed by the transition. The straight cylindrical channels in the ε form, which may be used for the separation of organic solvents, were rearranged to narrower zigzag channels in the S-I form, which is suitable for the precise separation of gases. The molecular cavities disappeared after release of the stress, associated with the transition to the γ form.