SCATTERING OF GASES FROM ALIGNED LIQUID-CRYSTALS - COLLISION-INDUCED LOSS OF ORDER AT THE GAS-LIQUID INTERFACE

An atomic beam of helium is scattered from the surface of an aligned n ematic liquid crystal film (4'-pentyl-4-cyanbo biphenyl, 5CB). Collisi ons of atoms with the surface initiate a transient loss of order in th e film. The magnitude of this change depends on the momentum direction of the atomic beam with respect to the liquid crystal alignment direc tor. The effect is significantly more pronounced when the incoming bea m is perpendicular to the director than when it is parallel. This anis otropy may be due to a more efficient alignment-changing torque exerte d on the 5CB molecules by perpendicular collisions with He. (C) 1996 A merican Institute of Physics.