Abstract
Photo-embossing has been developed as a convenient and economical method for creating complex surface relief structures in polymer films. The pursuit for large aspect ratios of the photo-embossed structures has never stopped. Here, we demonstrate a simple strategy to obtain improved aspect ratios by adding a quick solvent developing step into the photo-embossing process. A good solvent for the monomer is used to remove unreacted monomers from the unexposed region, resulting in deepened valleys of the surface reliefs. In a polymer film as thin as 2.5 µm, the height of the surface reliefs can be increased by a factor of three to around 1.0 µm. This strategy is also shown to be compatible with other methods used to improve the aspect ratios of the photo-embossed structures. Lastly, we employ these surface relief structures in the fabrication of liquid crystal (LC) devices and investigate their performances for visible light regulation.
Highlights
Liquid crystals (LCs), as a classic soft material, demonstrate a rich variety of intriguing optical, electrical, and magnetic properties, as well as stimuli-responsiveness, making them ideal candidates for the next-generation smart materials and devices [1,2,3,4]
Surface topography has been broadly used as a simple tool to produce uniform or patterned alignment in nematic LCs, and to control the molecular alignment and topological defects in smectic LCs or LC polymers [6,10,11,12,13]
Other than aligning the LCs, random surface topography is studied for its effect on enhancing the haze of a light-regulating smart window based on the polymer-stabilized liquid crystals (PSLCs) [23]
Summary
Liquid crystals (LCs), as a classic soft material, demonstrate a rich variety of intriguing optical, electrical, and magnetic properties, as well as stimuli-responsiveness, making them ideal candidates for the next-generation smart materials and devices [1,2,3,4] Owing to their anisotropic molecular shape, LC materials are highly sensitive to surface chemistry, geometric confinement, surface topography, and external stimuli such as heat, light, and electric or magnetic fields [5,6,7,8,9]. By introducing a quick solvent developing step, the aspect ratio can be improved by a factor of 3 This factor could be further enlarged if combined with other strategies such as using inhibitors or chain transfer agents in the free radical polymerization. The PSLC device was prepared following our previous report [37], using the LC monomer HCM-009 (Figure 1)
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