The surface-induced static director distribution in thin nematic liquid crystal films: A deuterium nuclear magnetic resonance spectroscopy study

We have studied the static director distribution in thin nematic liquid cry stal cells with different film thicknesses and different surface anchoring strengths using a combination of deuterium nuclear magnetic resonance (NMR) spectroscopy and continuum theory. A nematic liquid crystal, 4-pentyl-d(2) -4'-cyanobiphenyl (5CB-d(2)) deuteriated in the ct position of:the pentyl c hain, was confined between two glass plates with both weak and strong ancho ring conditions; the anchoring strengths were measured by using a saturatio n voltage method. A series of deuterium NMR spectra, obtained using a quadr upolar echo sequence, was acquired as a function of the applied electric fi eld, which can be used to explore the:director deformation. The deuterium N MR spectra predicted by continuum theory involving the magnetic, electric, elastic, and unified surface anchoring energies are found to be in good agr eement with experiment. The investigation also reveals that profiles of the director distribution for the case with a magnetic field have a top-hat sh ape different to the bowler-hat shape, which is well known as the director profile for the case with no magnetic field. (C) 2001 American Institute of Physics.