Functional soft materials with controlled molecular alignment are attracting much attention in various fields due to their excellent flexibility and functional properties. Among conventional alignment methods, mechanical methods such as rubbing the polymer surface are well-known as a facile route to align various molecules. Besides, photoalignment methods, using photoresponsive molecules and polarized light, enable precise alignment control towards advanced functions. As a novel alignment method combining the advantages of both mechanical and photoalignment methods, we have developed scanning wave photopolymerization (SWaP) where phototriggered molecular diffusion is applied to align molecules. Since it uses the molecular diffusion as a driving force for alignment control, SWaP has the potential to align a variety of molecules. For further exploration of the mechanism, it is necessary to understand the polymer properties; thus, the synthesis of polymers applicable to solution-based analyses is highly desired. In this study, we conducted SWaP to synthesize soluble liquid-crystalline polymer films with one-dimensional alignment. Furthermore, we compared the molecular alignment behavior between SWaP and the conventional rubbing alignment technique using a soluble polymer, and revealed that only SWaP can induce a unidirectional molecular alignment in film.
Macroscopic and precise alignment control of functional molecules represented by liquid crystals (LCs) and polymers is the key to generating a new function and enhancing their performances. Among various alignment techniques, a photoalignment method offers the greatest potential to finely control molecular alignment because of the capability of micro- to nano-patterning with remote processes. Recently, we have proposed a novel photoalignment method based on a new concept of scanning wave photopolymerization (SWaP). This method utilizes molecular diffusion triggered by the localized photopolymerization, enabling to generate an arbitrary alignment patterns merely by single-step photo-irradiation. In this study, we fabricated liquid-crystalline polymer networks directed by SWaP.
Inorganic materials such as nanotubes and nanorods have attracted much attention due to their anisotropic properties. Although controlling the alignment of inorganic materials is able to enhance their functionality, macroscopic alignment over a large area remains a challenge. We have recently proposed a simple method for inducing unidirectional alignment of ZnO nanorods on a rubbed polyimide layer. In this method, ZnO nanorods grafted with liquid-crystalline (LC) polymers are aligned by cooperative interaction between the LC moieties in the grafted polymers and surrounding LC host molecules. In this study, we investigated the unidirectional alignment of surface-modified ZnO nanorods in nematic LCs in a micrometer-thick cells. Alignment of LC polymer-grafted ZnO nanorods along nematic LC host molecules has been revealed by polarized optical micrography and ultraviolet-visible absorption spectroscopy.
Molecular alignment control in polymer films is key to the development of high-performance materials with optical, electronic and thermal functions. Among molecular alignment techniques, a photoalignment method offers the fine and remote control of two-dimensional molecular alignment by the irradiation with linearly polarized light. We have recently proposed a novel photoalignment method based on the molecular diffusion caused by the polymer concentration gradient, termed scanning wave photopolymerization. In this study, we report specific polymerization behavior occurring during the process of the scanning wave photopolymerization. We investigate the effect of molecular diffusion on the photopolymerization behavior by measuring molecular weight of the polymers obtained under various photopolymerization conditions.
The control of molecular alignment patterns in liquid crystals is key to developing high-performance optical devices. In particular, two-dimensionally designed patterns have attracted much attention due to their potential application to novel optical devices such as a high efficiency polarization grating and a vortex converter. However, there remain challenges in obtaining molecular alignment patterns by a simple method. We have recently proposed a novel method for controlling the alignment of liquid crystals termed scanning wave photopolymerization (SWaP). In this method, a mass flow triggered by spatiotemporal photopolymerization causes shear stresses to anisotropic molecules, resulting in the generation of alignment patterns finely guided by the scanned light. In this study, we present the direct fabrication of polymer films with cycloidal molecular alignment patterns by SWaP.
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