Confinement Induced Polarization effects in Valence and Inner-shell Spectra of Atactic Polystyrene

TL;DR

This study reveals that atactic polystyrene films below 4 times their radius of gyration exhibit polarization effects indicating macroscopic benzene ring alignment, transitioning from disordered to ordered phases under confinement.

Contribution

It demonstrates confinement-induced polarization effects and orientational ordering of benzene rings in atactic polystyrene films, confirmed by VUV and NEXAFS spectroscopy.

Findings

Benzene rings align macroscopically in thin films

Out-of-plane tilt angle of rings is approximately 63 degrees

Polymer transitions from disordered to ordered phase under confinement

Abstract

Vacuum ultraviolet (VUV) transmission spectra show a clear polarization effect in pi electronic transition in spin coated atactic polystyrene (aPS) films of thickness below 4Rg, where Rg (~20.4nm) is the radius of gyration of the polymer. This transition associated with pendant benzene rings in polystyrene. The polarization effect clearly indicates pendant benzene ring alignment on a macroscopic scale. Study of core electron (1s) transition through near edge x-ray absorption fine structure (NEXAFS) spectroscopy confirms the ordering and shows that the rings are oriented towards out-of-plane direction with a tilt angle ~63 degree with the sample plane, which is consistent with the observed in-plane (sample surface) VUV polarization. These results indicate the transition of a common polymer, like polystyrene, inherently disordered in the bulk, to an orientationally ordered phase under a certain degree of confinement.