Vapor interfaces, nematic

To reduce the free energy contributed by the surface tension term, the molecules at the liquid crystal/vapor interface favor a layer structure. In the smectic phase, the outermost layers favor a better molecular packing than exists in the interior. The enhanced surface order has been reported for various liquid crystal phases, for example the surface SmA order on the bulk isotropic or nematic sample [50] the surface SmI order on a SmA film [47] the surface SmB gx order on a SmA film [45,48] the surface SmI on a SmC film [17,93] the surface B on a SmA film [49] the surface crystal E order on a SmBhex film [100]. Realizing the importance of the surface tension in characterizing the liquid crystal free-standing films, we... 

The case of the interface with an isotropic or vapor phase is relatively simple in that no interaction with a substrate is involved. The molecular ordering and the orientation of the nematic director at these interfaces arise mainly from the change in density and type of order taking place across the interface. 

The examples of multistable anchorings and of anchoring transition reported above raise numerous fundamental questions concerning the structure of the interface between the nematic layer and the crystalline support. The existence of the anchoring transitions induced by variations of the water vapor pressure indicates clearly that adsorption of water molecules assists (or induces) variations of the anchoring direction. It must be so for following reasons. For a constant temperature T, only the chemical potential of water varies as a function of the partial pressure (variations of the partial... 

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