X-ray diffraction reveals the consequences of strong deformation in thin smectic films: dilation and chevron formation

TL;DR

This study uses X-ray diffraction and nonlinear energy modeling to analyze how strong deformation affects the structure of thin smectic films, revealing layer dilation, tilt, and chevron formation with high precision.

Contribution

It introduces a nonlinear energy framework to accurately describe layer dilation and structure in highly deformed smectic films, supported by quantitative X-ray data.

Findings

Layer dilation up to 1.8% observed in bent smectic layers.

A 1° tilt of planar layers linked to curved layers was measured.

Quantitative determination of curved layer number and thickness achieved.

Abstract

Smectic liquid crystals can be viewed as model systems for lamellar structures for which there has been extensive theoretical development. We demonstrate that a nonlinear energy description is required with respect to the usual Landau-de Gennes elasticity in order to explain the observed layer spacing of highly curved smectic layers. Using X-ray diffraction we have quantitatively determined the dilation of bent layers distorted by antagonistic anchoring (as high as 1.8% of dilation for the most bent smectic layers) and accurately described it by the minimal nonlinear expression for energy. We observe a 1{\deg} tilt of planar layers that are connected to the curved layers. This value is consistent with simple energetic calculations, demonstrating how the bending energy impacts the overall structure of a thin distorted smectic film. Finally, we show that combined X-ray measurements and theoretical modeling allow for the quantitative determination of the number of curved smectic layers and of the resulting thickness of the dilated region with unprecedented precision.