The orientation of liquid crystal molecules is very sensitive towards contacting surfaces, and this phenomenon is critical during the fabrication of liquid crystal display panels, as well as optical and memory devices. To date, research has focused on designing and modifying solid surfaces. Here we report an approach to control the orientation of liquid crystals from the free (air) surface side: a skin layer at the free surface was prepared using a non-photoresponsive liquid crystalline polymer film by surface segregation or inkjet printing an azobenzene-containing liquid crystalline block copolymer. Both planar-planar and homoeotropic-planar mode patterns were readily generated. This strategy is applicable to various substrate systems, including inorganic substrates and flexible polymer films. These versatile processes require no modification of the substrate surface and are therefore expected to provide new opportunities for the fabrication of optical and mechanical devices based on liquid crystal alignment.

An orientational change from homeotropic to planar of liquid crystal (LC) mesogens and the microphase separation (MPS) domains is attained by the segregated skin layer at the free surface. This allows for an efficient in-plane photoalignment of the cylindrical domains. The surface segregation strategy is very simple and is therefore expected to open up new possibilities for the orientation control of various types of LC materials.

The surface effects and anchoring of liquid crystals (LCs) have long been significant concerns for material chemists and physicists.[1] The surface alignment of LCs by mechanical rubbing [2] is a widely recognized phenomenon and of particular significance in technological applications for display device fabrication.[3] Surface molecular orientations [4] and topographical grooves and undulations [5] of the substrate provide LC alignment effects. Furthermore, in the past two decades, the photoalignment of LCs on photoreactive polymer film surfaces by anisotropic irradiation [6] has become a significant method and an alternative to mechanical rubbing processes. The aligning substrates are not limited to polymer surfaces; various types of surfaces, such as hard inorganic materials [7] and soft bio-related interfaces, [8] can be used for the alignment induction. In addition to low-molecular-mass LCs, polymer LC materials are also aligned by the surface effect.[9] Despite the tremendous amount of accumulated knowledge and the number of potential applications, the surface alignment processes developed to date mostly involve manipulations on the surfaces of solid or condensed phases.Herein, we report on LC alignment alternation, which is attained by a modification of the free surface (air-film interface). The homeotropic surface anchoring effect and layer structuring at the free surface of calamitic LC molecules have been shown experimentally [10] and have been further verified by theoretical simulations.[11] To modify the free surface, the present approach adopts the surface segregation [12,13] of a small amount of a free-surface-active polymer. We demonstrate here that the coverage of the surface with the free-surface-active polymer leads to a homeotropic-to-parallel orientation change of LC mesogens, which further leads to an efficient in-plane photoalignment of microphase separation (MPS) domains of a relevant LC block copolymer by linearly polarized light (LPL).[14] With regard to the MPS alignment control, the important role of a top coat layer has recently been demonstrated by Bates et al. [15] In this case, a polar-to-nonpolar chemical conversion of the top layer is achieved to fulfill the requirement of spin-casting from an aqueous solvent and to provide a neutral (non-preferential) layer for the hydrophobic block copolymer during the annealing. In the present approach, in contrast, no additional coating procedure is required, providing a simple, versatile method for the desired alignment control of MPS domains.First, the alignment behavior of an LC azobenzene (Az) homopolymer (PAz in Figure 1 a; M n = 8.0 10 4 , M w /M n = 1.13, and g-43 8C-SmC-100 8C-SmA-120 8C-iso) was examined. A spincast film of PAz was prepared (thickness: 100-200 nm) from a chloroform solution. After annealing at 130 8C (above the isotropization temperature) for 10 min followed by gradual cooling via a smectic LC phase to room temperature, this film spontaneously formed the out-of-plane (perpendicular) orientation of Az side mesogens, a...

Nanofibers of tetrafluoroethylene-perfluoroalkyl vinylether (PFA) copolymer were prepared by irradiating PFA fibers with a CO 2 laser under supersonic velocities. This is the only method to make PFA nanofibers without the use of solvents, because for the majority of methods for preparing nanofibers, they must be dissolved in a solvent and PFA fibers cannot be dissolved in most solvents, except special fluorinating reagents. The average fiber diameter of PFA nanofibers was approximately 273 nm. As a result, we developed a CO 2 laser supersonic multidrawing (CLSMD) in a new way to produce PFA nanofibers in large quantities. CLSMD can make nanofibers continually in a wide area. The length, width, and thickness of pileup nanofiber sheets are 50 cm, 17 cm, and 70 μm, respectively. It was observed that nanofiber sheets have a higher melting point and degree of crystallinity than microfibers by differential scanning calorimetry (DSC) measurements and have larger crystallite size realized by wide-angle X-ray diffraction (WAXD) measurements. Moreover, it was considered that the interior of nanofiber sheets have oriented structurally and the strength of nanofiber sheets was higher than that of microfibers. Nanoparticles were evolved to the surface of nanofiber sheets by annealing.

Investigations on the photoaglinment processes of liquid crystalline materials started around 25 years ago, and currently great developments have been made in both academic and industrial areas. However, there remain many issues to be explored in this field. This short review introduces our recent advances regarding the photoalignment and realignment process using azobenzene-containing liquid crystalline polymer materials. Two topics are involved here: the photoalignment of microphase separation structures of block copolymer films, and photoalignment controls from the free surface of a liquid crystalline polymer film.