Alignment Control of Smectic Layer Structures in Liquid-Crystalline Polymers by Photopolymerization with Scanned Slit Light

Abstract

Photoalignment control of hierarchical structures is a key process to enhance the properties of optical and mechanical materials. We developed an in situ molecular alignment method, where photopolymerization with the scanned slit light causes molecular flow, leading to two-dimensional precise alignment of molecules over large areas; however, the alignment control has been explored only on a molecular scale. In this study, we demonstrate this photopolymerization-induced molecular flow, enabling mesoscopic alignment of smectic layer structures composed of anisotropic molecules. Side-chain liquid-crystalline polymers were obtained from two different monomers with or without alkyl spacers by photopolymerization with one-dimensionally scanned slit light. The polymer with an alkyl spacer displayed mesogens aligned parallel to the scanning direction, while the polymer with no alkyl spacer resulted in perpendicular alignment of mesogens to the scanning direction, regulated by the alignment of the polymer main chain along the light scanning direction. Moreover, the polymerization with the scanned light aligned not only the mesogens but also mesoscopic smectic layer structures over large areas, depending on the structure and scanning pattern of light. We envision that such a simple polymerization technique could become a powerful and versatile alignment platform of anisotropic materials in a wide range of scales.

Direct Surface Patterning of Microscale Well and Canal Structures by Photopolymerization of Liquid Crystals with Structured Light

“…The FTIR spectra were gathered from 500 to 4000 cm –1 with a resolution of 4 cm –1 . The polymerization conversion of the sample was calculated by the following equation. ( 1 − A P : C  C / A P : C  N A M : C  C / A M : C  N ) × 100 where A x : y ( x = P for polymer and M for monomer; y = bond types) is the absorbance of the stretching vibrations of CC at 1619–1651 cm –1 and that of the stretching vibrations of CN at 2197–2234 cm –1 . , Figure S4 shows the conversion of the sample films as a function of the exposure dose (= [light intensity]·[irradiation time]). Then, POM observations of all sample cells were performed to determine their LC properties at a temperature of 100 °C.…”

“…Recently, we reported that photopolymerization-induced mass transport can produce surface structures of several hundred nanometers in depth. − Furthermore, we found that photopolymerization with scanning slit light causes mutual molecular diffusion between polymers and monomers and that the diffusion is maintained in a steady state by the scanning light, leading to a continuous molecular flow. Of particular interest here is that the molecular flow enables the alignment of polymer main-chain and side-chain mesogens along the flow direction, and the resultant polymer film has a flat surface without any change of surface topographies. − This interesting phenomenon of photopolymerization induced by molecular diffusion has the potential for creating novel surface topography; however, its detailed investigation remains unexplored.…”

“…where A x:y (x = P for polymer and M for monomer; y = bond types) is the absorbance of the stretching vibrations of C�C at 1619−1651 cm −1 and that of the stretching vibrations of C�N at 2197−2234 cm −1 23,30. FigureS4shows the conversion of the sample films as a function of the exposure dose (= [light intensity]•[irradiation time]).…”

Cooperative Liquid Crystal Photo‐Polymerization and ‐Alignment with In Situ Monitoring for Substrate Independent Patterning of Optical Anisotropy

“…Alternatively, scanning-wave photoalignment has been demonstrated as a dye-free route to LC patterning, yet it requires a specialized setup for light-rastering. [29,30] In both surface-and polymer-mediated processes, photoalignment is often accomplished using LPL exposure of samples in the nematic mesophase (i.e., elevated temperatures), [31] where the presence of directional order, yet lack of positional order enables cooperative molecular reorientation. Additionally, photo-alignment and/or -polymerization are often (although not exclusively [32] ) accomplished using multistep high energy (UV) and/or intensity (≥100 mW cm −2 ) irradiation, [11,15] providing opportunities for improvement.…”

Self-Assembly of Peptide-Conjugated Forklike Mesogens at Aqueous/Liquid Crystalline Interfaces: Molecular Design for Ordering Transition Induced by Specific Binding of Biomolecules

“…Self-assembly of liquid crystals has attracted considerable attention as an approach to the development of functional soft materials. – A variety of dynamic and ordered liquid crystalline (LC) materials have been obtained based on their responsiveness to external stimuli such as heat, light, and electric fields. – Interactions on solid surfaces have also been used to induce ordering transitions of the dynamic LC assemblies. – Active LC thin films have been developed for on-demand patterning with precise molecular alignment. – The combination of self-assembly of liquid crystals with molecular recognition at the interfaces allows preparation of LC systems that respond to target molecules. – In particular, aqueous/LC interfaces have been studied as platforms to recognize biomolecules because they can amplify biomolecular interactions into macroscopic optical signals. – The control of self-assembly of bioconjugated amphiphilic molecules at the aqueous/LC interfaces remains a challenge, although understanding of the behavior of LC assemblies is advancing in terms of molecular shape, intermolecular interactions, and nanosegregation. ,,– Intensive studies have focused on molecular-level phenomena at liquid and solid interfaces to understand relationships between molecular design and dynamic interfacial behavior. ,, …”