Viscoelastic PS brush surface offering strong anchoring at low temperature and near-zero anchoring at high temperature for LC molecules

Abstract

The orientation behaviour of a nematic liquid crystal (LC) was examined in a cell consisting of two substrates on which polystyrene (PS) chains were grafted with a high density of 0.43 chains nm⁻². A planar orientation of the LC was obtained in this cell and a uniform LC domain was achieved on slowly cooling the LC from the isotropic state to room temperature in a magnetic field. The PS brushes exhibited temperature-variant surface properties whereby they functioned as a strong anchoring surface at ambient temperature, viscoelastic anchoring surface at higher temperatures ranging from 45°C to 85°C and near-zero anchoring surface at 110°C (near the isotropisation temperature (T_i ) of the bulk nematic). Among these temperature-variant surfaces, the zero anchoring one is useful not only for the development of new LCD modes with novel non-contact orientation capabilities but also for the formation of an ultra-low friction interface with potential applications in number of fields.

Keywords:

• surface anchoring
• polymer brush
• zero-anchoring
• LC alignment