Photoinduced 3D orientational order in side chain liquid crystalline azopolymers

TL;DR

This study investigates the 3D orientational order induced by light in liquid crystalline azopolymers using combined optical methods, revealing how different wavelengths influence the photoinduced anisotropy mechanisms.

Contribution

It introduces a novel experimental technique for 3D order characterization and develops a phenomenological model explaining wavelength-dependent anisotropy mechanisms.

Findings

The technique identifies 3D orientational configurations and degrees of order.

Photoinduced anisotropy mechanisms depend on irradiation wavelength.

Numerical results align well with experimental data.

Abstract

We apply experimental technique based on the combination of methods dealing with principal refractive indices and absorption coefficients to study the photoinduced 3D orientational order in the films of liquid crystalline (LC) azopolymers. The technique is used to identify 3D orientational configurations of trans azobenzene chromophores and to characterize the degree of ordering in terms of order parameters. We study two types of LC azopolymers which form structures with preferred in-plane and out-of-plane alignment of azochromophores, correspondingly. Using irradiation with the polarized light of two different wavelengths we find that the kinetics of photoinduced anisotropy can be dominated by either photo-reorientation or photoselection mechanisms depending on the wavelength. We formulate the phenomenological model describing the kinetics of photoinduced anisotropy in terms of the isomer concentrations and the order parameter tensor. We present the numerical results for absorption coefficients that are found to be in good agreement with the experimental data. The model is also used to interpret the effect of changing the mechanism with the wavelength of the pumping light.