Photoinduced motions in azo-containing polymers.

A simple technique is described here that produces aligned arrays of carbon nanotubes. The alignment method is based on cutting thin slices (50 to 200 nanometers) of a nanotube-polymer composite. With this parallel and well-separated configuration of nanotubes it should be possible to measure individual tube properties and to demonstrate applications. The results demonstrate the nature of rheology, on nanometer scales, in composite media and flow-induced anisotropy produced by the cutting process. The fact that nanotubes do not break and are straightened after the cutting process also suggests that they have excellent mechanical properties.

https://science.sciencemag.org/content/sci/265/5176/1212.full.pdf

Aligned Carbon Nanotube Arrays Formed by Cutting a Polymer Resin—Nanotube Composite

Photoalignment of Liquid-Crystal Systems.

Three-Dimensional Optical Data Storage Using Photochromic Materials.

THE leading technology for flat, high-resolution computer and television screens is based on twisted nematic liquid-crystal displays1. The successful operation of these displays requires control of molecular alignment, which is currently achieved by confining the liquid crystal between mechanically rubbed surfaces2. But in addition to the practical difficulties associated with rubbing, the resulting displays suffer from restricted viewing angles arising from the uniaxial nature of the alignment process3,4. This latter problem can in principle be circumvented if molecular alignment is varied, in a controlled manner, within individual pixels5–9. Exposure of functionalized substrates to polarized light offers a means of achieving high-resolution patterns in the plane of the display10–12. But to ensure that the alignment pattern imposed on the liquid crystal is free of orientation defects, the tilt angle between the long molecular axes and the substrates must be precisely controlled13,14. Here we show how our earlier linear photoalignment strategy10,12 can be extended to obtain such control, and thereby fabricate stable, multi-domain pixel displays with markedly improved fields of view.

Optical patterning of multi-domain liquid-crystal displays with wide viewing angles

THE control of molecular alignment in liquid-crystal phases at macroscopic scales has been investigated extensively because of its importance in optical or optoelectronic applications, such as liquid-crystal displays1. It is well established that liquid crystals can be aligned by an applied electric field, a magnetic field, a shear-flow field, mechanical grooving of the substrate surface or stretching of liquid-crystal polymer thin films2,3. Here we report a new mechanism for liquid-crystal alignment that uses polarized laser light. We find that nematic liquid crystals in an illuminated region become oriented perpendicular to the direction of the electric-field polarization of the laser and remain aligned in the absence of the laser radiation. The liquid crystals can be reoriented again by subsequent illumination. This technique might have applications for large-area displays, optical memories, binary optics, adaptive optics and molecular micro-assembly.

Surface-mediated alignment of nematic liquid crystals with polarized laser light

MOST practical applications of liquid crystals require control of molecular alignment at macroscopic scales1. This is achieved most simply by confining the liquid-crystalline phase between mechanically rubbed surfaces1. Recent developments2–11 have shown that liquid-crystal alignment can also be controlled by optical means: for example, if azo dyes either on the alignment surface2,3,5,8–11 or dispersed within the liquid crystal itself4,6,7 are oriented by illumination with polarized light, alignment can be induced in the liquid crystal. We show here that the high-resolution alignment patterns obtainable by such techniques may be 'frozen in' by subsequent photopolymerization of the optically patterned liquid-crystalline phase. The resulting polymer films might prove valuable in the development of high-density optical storage media, three-dimensional stereo displays and other optical devices.

Patterned optical properties in photopolymerized surface-aligned liquid-crystal films

A liquid crystal polymer film or fiber comprising polymeric liquid crystals having aligned multiple oriented mesogens and a process for preparing such a polymeric liquid crystal film or fiber comprising aligning in a multi-oriented state a nematic or smectic monomeric mesophase (liquid crystal monomer) and photopolymerizing the mesophase, are disclosed. The film or fiber may be adhered to a substrate, part of a liquid crystal display cell, or a free standing polymeric film or fiber. According to a preferred process, the mesophase is aligned in a multi-oriented state using linearly polarized light.

Process of preparing compositions having multiple oriented mesogens

Optically controlled planar orientation of liquid crystal molecules with polarized light is used to make phase gratings in liquid crystal media. The electro‐optical properties of liquid crystal linear and chirped gratings are discussed.

Optically generated liquid crystal gratings

Surface-mediated alignment of nematic liquid crystals with polarized laser light was reported recently [1]. In this communication we describe the alignment of a guest–host liquid crystal medium with polarized laser light. Liquid crystals in the illuminated region orient perpendicular to the direction of the laser polarization and remain aligned in the absence of laser radiation. The liquid crystals can be reoriented again by subsequent illumination. The kinetic feature of this surface-mediated liquid crystal orientation is characterized by the presence of coexisting liquid crystal regions of directors pointing away from the initial alignment.

Shao-Tang Sun

Papers

Surface-mediated alignment of nematic liquid crystals with polarized laser light

Patterned optical properties in photopolymerized surface-aligned liquid-crystal films

Process of preparing compositions having multiple oriented mesogens

Optically generated liquid crystal gratings

Alignment of guest–host liquid crystals with polarized laser light