Alignment layer-free molecular ordering induced by masked photopolymerization with non-polarized light

Abstract

Controlled and uniform molecular alignment can provide and enhance functionality in polymer films. We first report that masked photopolymerization with non-polarized light enables direct and precise control of molecular alignment without using a conventional molecular alignment layer. The photopolymerization of a mixture composed of an optically anisotropic acrylate monomer and an isotropic dimethacrylate crosslinker induces either unidirectional or complex molecular alignment, depending upon the shape of the photomask. Such molecular alignments are successfully achieved by shear stress arising from molecular diffusion, even when the photopolymerization is carried out at isotropic temperatures of both the monomer mixture and the obtained polymers.

Scanning wave photopolymerization enables dye-free alignment patterning of liquid crystals

“…As a further advantage over other current techniques, the size of the final alignment patterns would be, in principle, restricted only by light diffraction limits, and complexity of any patterns in 2D is then effectively unlimited. Previously, we had serendipitously found a key related effect that leads to the development of the present SWaP concept, where photopolymerization through a spatially patterned photomask led to an unexpected molecular alignment at the pattern edges ( 38 ), and this unusual driving force was suspected to be a mass flow of molecular diffusion in a light intensity gradient ( 39 – 43 ). This was an exciting initial discovery with potential for development; however, the detailed mechanism of the underlying process was unclear, and using masks limited the size of alignment achievable to a scale of hundreds of micrometers and constrained the variety of alignment patterns possible to those of preformed masks available.…”

Photoinduced Reorientation and Photofunctional Control of Liquid Crystalline Copolymers with in Situ-Formed N-Benzylideneaniline Derivative Side Groups

“…Many types of photosensitive materials have been explored to investigate photoinduced reorientation based on axis-selective trans–cis–trans photoisomerization of azobenzene-containing materials using LP light. − Photoreactive LC polymers containing cinnamate or phenyl benzoate mesogenic side groups exhibit a thermally stimulated photoinduced molecular reorientation, which is initiated by axis-selective photo-cross-linking or photo-Fries rearrangement. − Additionally, a new molecular orientation technique for photoinactive LC polymeric films from a free (air) surface using an azobenzene-containing polymer realizes a photoinduced molecular orientation of the inner side of the polymers and precise patterning. − Furthermore, Shishido et al have reported that dynamic photopolymerization attains molecularly oriented structures of the LC polymeric films, where the self-organized orientation of the mesogenic side groups occurs at the interface between the monomer and polymer using methacrylate monomers with mesogenic side groups. − These molecularly oriented films are applicable to birefringent optical devices and polarization-sensitive and polarization-controlled diffraction gratings when the film contains a periodical molecular orientation structure. ,,− …”

Localized Liquid Secretion from a Photopatterned Liquid-Crystal Polymer Skin

“…This is a typical phenomenon inherent to the first maskwise photopolymerization and originates from the polymerization-induced diffusion process . This process forms the base of photoembossed surface topographies − and is used to create a 3D morphing film in hydrogels. , In a simplified model, polymerization-induced diffusion is initiated by local differences in light intensity during the photopolymerization process in a monomer mixture containing monomers with different polymerization and/or diffusion rates. , It is therefore expected that the smectic area is enriched by a higher concentration of the responsive azobenzene molecules, possibly at the expense of some of the nonreactive molecule 3 .…”