Topographically induced homeotropic alignment of liquid crystals on self-assembled opal crystals

Abstract

The surface of multilayered opal crystals resulted in homeotropic alignment of liquid crystal (LC), originated from the surface topography of opal crystals rather than a chemical nature of the nanoparticles. The polar anchoring energy (5.51 × 10 J/m) of the crystal surface for nematic LC molecules was in a similar range to the conventional polyimide alignment layer (2.11 × 10 J/m) used for commercial applications. The critical length scale for anchoring transition was approximately Lw = ~1 μm. If a diameter of particle d << 1 μm for opal crystals, LC molecules preferred to anchor vertically to the surface to minimize elastic free energy of bulk LCs. The LC favored a planar anchoring if d >> 1 μm. The results provide crucial insights to understand the homeotropic alignment of LCs on solid surfaces and therefore offer opportunities to develop novel materials for a vertical alignment of LCs.

Electrically controlled topological micro cargo transportation

“…This provided mechanical nano-groove planar alignment of the nematic liquid crystal with a negligible pretilt angle. 21 Inorganic thin solid films, for example silicon dioxide and associated solid dielectrics, commonly provide a polar anchoring energy of the order of 10 À5 J m À2 22 similar to conventional polyimide 23 and polyvinyl alcohol alignment layers. 24 Magnesium fluoride thin films have previously been used to align twisted nematic cells in the literature, giving a comparable electro-optical performance to polyimide alignment layers.…”

Fullerene-Based Nanosurfactant for the Automatic Homeotropic Alignment of Liquid Crystals

“…Consequently, a surface topology change leads to a HA state by inducing a sufficient degree of elastic distortion to surpass the effects of surface anchoring. 15 The evidence about the surface morphology is going to be dealt with in surface analysis.…”

Using Liquid Crystals to Probe the Organization of Helical Polypeptide Brushes Induced by Solvent Pretreatment

“…This is supported by our observation that chloroform-treated 140 nmthick brushes, which exhibit an rms roughness of 2.1 ± 0.2 nm, induces planar LC alignment, while chloroform-treated 12 nmthick brushes, which exhibit an rms roughness of 2.3 ± 0.2 nm, induce homeotropic alignment. Prior studies 45 have reported that surface roughness can influence the orientations of LCs, but those studies employed surfaces with rms roughness values that were much larger than 2 nm.…”