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Temperature-Driven Anchoring Transitions at Liquid Crystal/Water Interfaces
journal contribution
posted on 2020-08-05, 20:16 authored by Guillaume Durey, Yoko Ishii, Teresa Lopez-LeonControlling the anchoring
of liquid crystal molecules at an interface
with a water solution influences the entire organization of the underlying
liquid crystal phase, which is crucial for many applications. The
simplest way to stabilize such interfaces is by fabricating liquid
crystal droplets in water; however, a greater sensitivity to interfacial
effects can be achieved using liquid crystal shells, that is, spherical
films of liquid crystal suspended in water. Anchoring transitions
on those systems are traditionally triggered by the adsorption of
surfactant molecules onto the interface, which is neither an instantaneous
nor a reversible process. In this study, we report the ability to
change the anchoring of 4-cyano-4′-pentylbiphenyl (5CB), one
of the most widely used liquid crystals, at the interface with dilute
water solutions of polyvinyl alcohol (PVA), a polymer commonly used
for stabilizing liquid crystal shells, simply by controlling the temperature
in the close vicinity of the liquid crystal clearing point. A quasi-static
increase in temperature triggers an instantaneous reorientation of
the molecules from parallel to perpendicular to the interfaces, owing
to the local disordering effect of PVA on 5CB, prior to the phase
transition of the bulk 5CB. We study this anchoring transition on
both flat suspended films and spherical shells of liquid crystals.
Switching anchoring entails a series of structural transformations
involving the formation of transient structures in which topological
defects are stabilized. The type of defect structure depends on the
topology of the film. This method has the ability to influence both
interfaces of the film nearly at the same time and can be applied
to transform an initially polydisperse group of nematic shells into
a monodisperse population of bivalent shells.