Transient response and domain formation in electrically deforming liquid crystal networks

TL;DR

This study investigates the transient dynamics of electrically deforming liquid crystal networks, revealing how film thickness and mesogen properties influence domain formation and response times, thereby aiding in better control of these smart materials.

Contribution

The paper provides a Landau-theoretical interpretation of transient regimes and identifies how to suppress domain formation by modifying film and mesogen properties.

Findings

Response regimes depend on film thickness and thermal noise.

Domain formation occurs at a critical transition point.

Reducing initial film thickness suppresses domain formation.

Abstract

Recently, Van der Kooij and co-workers recognised three distinct, transient regimes in the dynamics of electrically-deforming liquid crystal networks [Van der Kooij et al., Nat. Commun. 10, 1 (2019)]. Based on a Landau-theoretical framework, which encompasses spatially resolved information, we interpret these regimes: initially, the response is dominated by thermal noise, then the top of the film expands, followed by a permeation of this response into the bulk. An important signature of this interpretation is a significant dependence of the regime time scales on film thickness, where we observe a clear thin-film-to-bulk transition. The point of transition coincides with the emergence of spatial inhomogeneities in the bulk, i.e., domain formation, and should be avoided due to the less predictable steady-state expansion it gives rise to. Finally, we show that this domain formation can be suppressed by decreasing the initial thickness of the film, and increasing the linear dimensions of the mesogens, or their orientational order when crosslinked into the network, though this comes at the cost of the deformation magnitude. Our results contribute to achieving finer control over how smart liquid crystal network coatings are activated.