A Hexagonal Pillar Array of Thermo-responsive Soft Actuators Prepared by Nanoimprinting
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A Hexagonal Pillar Array of Thermo-responsive Soft Actuators Prepared by Nanoimprinting Ching-Mao Wu1*, Szu-Yin Lin1, and Kuo-Tung Huang1 1 Material and Chemical Research Laboratories, Industrial Technology Research Institute, Chutung, Hsinchu, Taiwan 31040
ABSTRACT Thermo-responsive actuation (thermomechanical effects) based on nematic liquid crystal elastomers (LCEs) have become a research priority in the preparation of soft actuators. Nematic LCEs combine the anisotropic features of liquid crystal phases with the rubber elasticity of polymer network. When heated at nematic to isotropic phase transition temperature (N-to-I temp.), a uniaxial thermomechanical deformation of LCEs will undergo at nearly constant volume due to a change of LC director order. Recently, an array of the micro-sized LCE pillars related to such thermomechanical effects have been successfully constructed through a soft lithography technology (i.e., replica molding). The prepared LCE pillars are mono-dispersive and micro-sized. They also possess N-to-I temp. higher than 100к, largely limiting the available application. By contrast, the present study will report a hexagonal array of nano-sized thermoresponsive pillar actuators that are able to contract and expand in response to temperature changes around a lower N-to-I temp. is manufactured via using reactive rod-like liquid crystal and ultraviolet nanoimprinting technology. According to atomic force microscope (AFM) observation, a hexagonal array of pillars can be easily constructed by nanoimprinting and a responsive surface with a thermo-stimuli-driven roughness change is achieved. The roomtemperature AFM scans quantitatively represent the single pillar shows a diameter of ca. 270 nm and 140 nm in depth, and the pitch meaning the averaged inter-pillar distance is measured as ca. 425 nm, thus lying in a nano-sized range. Furthermore, temperature-variable AFM is also utilized to demonstrate the pillar behaves as a thermally-stimulated nano-sized actuator. In our case, when heated above N-to-I phase transition temperature (ca. 65к), it is clearly observed that the pillar diameter is expanded in the order of over 12-15 % and then reversibly contracted in response to temperature drop. INTRODUCTION In the field of smart materials, the materials bearing thermo-stimuli-driven deformation in shape or size have received a lot of attention due to the recent scientific interests in preparing artificial muscles or actuators.1 Also, thermo-responsive actuation (thermomechanical effects) based on nematic liquid crystal elastomers (LCEs) have gradually become a research priority in the preparation of soft actuators.1-4 Nematic LCEs combine the anisotropic features of liquid crystal phases with the rubber elasticity of polymer network. When heated at temperature close to nematic to isotropic phase transition temperature (N-to-I temp.) of LCEs, a uniaxial thermomechanical deformation of LCEs will undergo at nearly constant volume due to a change of LC director order.3-5 Recently, Keller et al.’s pioneering s
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