Speaker: Ameer R.K. Nassrah (HUN-REN Wigner RCP SZFI)

Title: Photoalignment at Liquid Crystal–Polymer Interface

Date: Tuesday, 6 February 2024, 10:00

Place: KFKI Campus, Bldg. 1, 2nd floor, Conference Room


Proper, controllable alignment of the liquid crystal (LC) molecules at solid substrates is a key factor for correct operation of all LC-based devices. Photoalignment is a promising, contactless method of achieving the required alignment, which can be applied in enclosed areas (e.g., in microfluidic channels), and which avoids the drawbacks of mechanical contacts (e.g., mechanical damages, accumulation of ions and dust particles). In these photoaligning systems, a very small number of photochromic derivatives anchored on a substrate commands the alignment of a very large number of LC molecules in contact with it, and therefore, the surfaces were referred to as "command surfaces".

The experiments were focusing on the influence of the LC molecular structure and that of the LC phase on the photoalignment process. The results indicate the importance of both the LC structure and the phase [1,2]. An interaction mechanism has been proposed between the command surface and the LC molecules for the peculiar photoalignment properties of LCs with biphenyl rigid core. The proposed interaction mechanism has been validated by additional experimental results [2].

The dependence of the photoalignment on the composition of the command surface has also been tested. Drastic differences have been found in the efficiency of the photoalignment depending on the preparation method. AFM measurements have shown, that efficient photoalignment is accompanied with a significant photo-induced mass transfer [3].

[1] A.R.K. Nassrah, I. Jánossy and T. Tóth-Katona, "Photoalignment at the Nematic Liquid Crystal-Polymer Interface: The Importance of the Liquid Crystalline Molecular Structure." J. Mol. Liq., 312, 113309/1-7 (2020).
[2] A.R.K. Nassrah, I. Jánossy, V. Kenderesi, T. Tóth-Katona, "Polymer-Nematic Liquid Crystal Interface: On the Role of the Liquid Crystalline Molecular Structure and the Phase Sequence in Photoalignment." Polymers 13, 193/1-13 (2021).
[3] A.R.K. Nassrah, M. Batkova, N. Tomašovičová, T. Tóth-Katona, "Photoaligning Polymeric Command Surfaces: Bind, or Mix?" Polymers 15, 4271/1-12 (2023).