The use of mould-templated surface structures for high-quality uniform-lying-helix liquid-crystal alignment

Abstract

The chiral-flexoelectrooptic effect in a Uniform Lying Helix (ULH) configuration provides a sub-millisecond in-plane rotation of the optic axis with the application of a transverse field. This enables displays with a wide viewing angle without costly in-plane-type electrodes. The salient challenge is one of alignment of the ULH, which is not topologically compatible with uniform alignment surface treatments. Here, we create a micro-grooved surface structure with features on the micron scale by using a replica-moulding technique. When the cell is assembled, the micro-grooves create channels, and using surface-energy considerations, we explain how and show experimentally that the channels align a cholesteric material in the ULH geometry with the helicoidal axis oriented parallel to the channels. The resultant alignment provides a high level of contrast between crossed polarizers and exhibits an electrooptic response with a switching time of the order of tens of microseconds.

Stimuli‐Driven Control of the Helical Axis of Self‐Organized Soft Helical Superstructures

“…In the cells with homeotropic boundary conditions, it becomes challenging to achieve the ULH structure without additional influences. Subsequently, they used mold‐templated surface structures to achieve ULH structure . By assembling two microgrooved substrates, they fabricated an LC cell having microchannels.…”

15-3:Invited Paper: Liquid Crystal Technologies Towards Realising a Field Sequential Colour (FSC) Display

“…Such geometry cannot be easily matched to a uniform alignment surface without the formation of defects, thus reducing the potential quality of the dark state in a ULH display. A number of routes towards improving ULH alignment have been investigated in the past [9][10][11][12] .…”

Voltage-controlled formation of short pitch chiral liquid crystal structures based on high-resolution surface topography

“…In this case, besides the surface topography and surface chemistry, also the chiral pitch and the cell thickness strongly define the resulting director configuration. Previously Outram et al exploited surface topography for CLC alignment by creating a mold-templated surface to align a short pitch (p = 320 nm) uniform lying helix (ULH) [18]. The channel width and height was much larger than the chiral pitch in this case.…”

“…Surface topography has been studied as a tool for the alignment of especially NLC. Surface structures were made by nano-imprint lithography, soft embossing, replica moulding, laser scanning lithography, ion beam milling, nanosphere lithography and e-beam lithography [15][16][17][18][19][20][21][22][23][24]. Berreman explained that NLC molecules preferentially align parallel to the groove direction of a surface grating and not perpendicular to it [25].…”

“…More recently, the influence of surface topography on the alignment of CLC has also been investigated [18,19]. The behavior is much more complex because the grooves may have similar dimensions as the pitch of the CLC and the simple theory of Berreman does not apply anymore.…”