Photoinduced Mass Transport in Azo-Polymers in 2D: Monte Carlo Study of Polarization Effects.

Grzegorz Pawlik,Antoni C Mitus

doi:10.3390/ma13214724

Abstract

We studied the impact of light polarization on photoinduced dynamics of model azo-polymer chains in two dimensions, using bond-fluctuation Monte Carlo simulations. For two limiting models—sensitive to and independent of light polarization—their dynamics driven by photoisomerization of azo-dyes as well as by thermal effects was studied, including characterization of mass transport and chain reorientations. The corresponding schemes of light–matter interaction promote qualitatively different dynamics of photoinduced motion of azo-polymer chains. In particular, they can inhibit or trigger off a directed mass transport along a gradient of light illumination. The generic dynamics of single chains is superdiffusive and is promoted by breaking a symmetry present in the polarization independent model.

Highlights

Thin films of azobenzene functionalized polymers [1] exposed to interfering polarized laser beams in degenerated two wave mixing (DTWM) experiment may develop periodic surface corrugation pattern called surface relief gratings (SRGs) [2,3]
The macroscopic mass transport at the surface of polymer thin film at temperature far below the polymer glass transition temperature Tg is attributed to microscopic polymer chain movements which result from light-induced multiple trans ↔ cis photoisomerization cycles of azobenzene dyes attached to the chains
To develop a deeper intuition concerning the impact of light polarization on the Monte Carlo (MC) dynamics of azo-chains, we introduce, in contrast, a model which is fully insensitive to the polarization, in which the transition probability p is constant and independent on an actual orientation of an azo-dye

Summary

Introduction

Photoinduced Mass Transport in Functionalized Azo-Polymers Concepts. Thin films of azobenzene functionalized polymers [1] exposed to interfering polarized laser beams in degenerated two wave mixing (DTWM) experiment may develop periodic surface corrugation pattern called surface relief gratings (SRGs) [2,3]. The macroscopic mass transport at the surface of polymer thin film at temperature far below the polymer glass transition temperature Tg is attributed to microscopic polymer chain movements which result from light-induced multiple trans ↔ cis photoisomerization cycles of azobenzene dyes attached to the chains. The various general ideas and approaches include mean-field approach [6], pressure gradient scenario [7,8], photoexpansion and photocontraction effects [9], viscoelastic flow [10], inchworm-like motion [11], gradient force models [12,13], Navier–Stokes dynamics [14,15], random-walk approaches [16], stochastic models [17,18,19], light-induced softening [4,12], atomistic molecular dynamics simulations [20], and others

Objectives

Methods

Conclusion