  Controlling 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 droplets of liquid crystal in
water; however, a greater sensitivity to interfacial effects can be achieved
using liquid crystal shells, i.e. 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.
