Langmuir, Vol.12, No.10, 2587-2593, 1996
Uniform Anchoring of Nematic Liquid-Crystals on Self-Assembled Monolayers Formed from Alkanethiols on Obliquely Deposited Films of Gold
This paper demonstrates that self-assembled monolayers (SAMs) formed by chemisorption of alkanethiols on the surface of obliquely deposited, 10 nm-thick, films of gold are useful in studies of the anchoring of liquid crystals (LCs) on surfaces. Self-assembled monolayers supported on obliquely deposited gold permit uniform anchoring of nematic LCs over centimeter-scales. In contrast, SAMs prepared on films of gold deposited with no preferred direction cause nematic phases to form 10-100 mu m scale domains with optical axes having random azimuthal orientations. Self-assembled monolayers prepared from either CH3(CH2)(15)SH or CH3(CH2)(9)SH on films of gold deposited obliquely induce near-planar and azimuthally uniform anchoring of nematic phases of 4-cyano-4’-pentylbiphenyl (5CB). Mixed SAMs formed by coadsorption of CH3(CH2)(15)SH and CH3(CH2)(9)SH cause homeotropic anchoring of nematic phases of 5CB on films of gold deposited without a preferred direction and produce a small tilt (3-5 degrees) from the normal on gold deposited obliquely onto glass substrates. The contact angles (advancing and receding) of hexadecane are indistinguishable when measured on SAMs supported on gold with and without a preferred direction. Liquid crystals can be used to detect anisotropy in these surfaces that cannot be measured by the wetting of simple fluids such as hexadecane.
Keywords:ENERGY HELIUM DIFFRACTION;SURFACE-MORPHOLOGY;ORGANIC-SURFACES;ORIENTATION;MICROSCOPY;THIOLS;TOPOGRAPHY;MOLECULES;ALIGNMENT;AU(111)