Observation of surface and bulk phase transitions in nematic liquid crystals

Abstract

The behaviour of liquid crystal (LC) molecules near a surface is of both fundamental and technological interest: it gives rise to various surface phase-transition and wetting phenomena, and surface-induced ordering of the LC molecules is integral to the operation of LC displays. Here we report the observation of a pure isotropic-nematic (IN) surface phase transition-clearly separated from the bulk IN transition-in a nematic LC on a substrate. Differences in phase behaviour between surface and bulk are expected, but have hitherto proved difficult to distinguish, owing in part to the close proximity of their transition temperatures. We have overcome these difficulties by using a mixture of nematic LCs: small, surface-induced composition variations lead to complete separation of the surface and bulk transitions, which we then study independently as a function of substrate and applied magnetic field. We find the surface IN transition to be of first order on surfaces with a weak anchoring energy and continuous on surfaces with a strong anchoring. We show that the presence of high magnetic fields does not change the surface IN transition temperature, whereas the bulk IN transition temperature increases with field. We attribute this to the interaction energy between the surface and bulk phases, which is tuned by magnetic-field-induced order in the surface-wetting layer.

Alignment of Liquid Crystals Using a Molecular Layer with Patterned Molecular Density

“…[ 22 ] Other examples showing different T NI values at the surface and in bulk have also been reported. [23][24][25] In conclusion, LCs near the SDM layer exhibited a stable Iso layer over a wide area while the bulk LCs were still in the nematic phase. Thus, the LCs with the heterogeneous boundary exhibited N-Iso phase separation at the SAM surface.…”

Unravelling adsorption and alignment of amyloid fibrils at interfaces by probe particle tracking

“…[1][2][3] Despite the great advances in the theoretical understanding of this process over the last four decades, 4-7 the corresponding experimental progress has been remarkably slow. 8 As per today, the establishment of a robust experimental route to the detection of two-dimensional structural changes at fluid interfaces, such as the 2D isotropicnematic transition, which is at the same time generally applicable and non-invasive, has yet to be found.…”

Orientational order in binary mixtures of hard Gaussian overlap molecules

“…Since small-weight molecules can response very fast to the variation of external fields, the small-molecular-weight LCs would be of great advantage in many applications. However, in simple confined geometry, the surface-induced effects are limited to the several molecular layers neighboring the surfaces of the confining walls [3,8], but in complex confined geometry, we may expect surface-induced effects in whole fluids.…”