Carrier diffusivity of a lithium electrolyte solution in porous membranes was evaluated by observation of diffusion behavior of ionic species using NMR spectroscopy. We performed analysis on the basis of the restricted diffusion model and a new idea of diffusion distribution. That new concept is engendered in the assumption that observed diffusion values are distributed according to pore size distribution and nonuniformity of pore and polymer density in a membrane. Carrier diffusivity in polyethylene (PE) porous membranes showed characteristic echo attenuation, which differs from echo behavior as a result of random walk migration. We first tried to simulate the echo change on the basis of the restricted diffusion model in porous structure, resulting in disagreement with the observed echo change. As a result, the idea that diffusion values are distributed concurrent with porous geometry was applied to interpret the situation. Introduction of a Gaussian function to represent the distributed condition yielded highly reproducible results for the membranes. Carrier diffusivity in porous PVDF membranes showed a narrow distribution compared with that of PE membrane. The swelling feature of the PVDF polymer would contribute to averaging the pore size and preparing the uniform network for carrier transport pathway.
Limitations in further miniaturization of lenses and arrays to achieve varifocal capabilities in compact 2D/3D switchable imaging devices have spurred investigations into the use of alternative materials. To this end, we fabricated a new deformable microlens array (MLA) utilizing polyvinyl chloride (PVC) gel, containing 67–90 wt.% of dibutyl adipate (DBA), sandwiched between an anode with apertures, 20–300 μm in diameter, and a cathode made of a transparent conductive film. The effects of applied voltage and DBA content on the protrusion of the PVC gel were studied and the protrusion mechanism was investigated. The gel was deformed from a flat shape in the absence of voltage to a lens shape at 100–600 V. When a voltage was applied, the negatively charged PVC chains accumulated near the anode and induced deformation of the PVC gel, which rose along the aperture walls and protruded from the apertures. Furthermore, the protrusion level of the PVC gel increased with DBA content, which lowered its elastic modulus and increased the negative charge density. Thus, the deformation of the PVC gel was mainly governed by the effects of electrostriction and PVC chain dynamics. Additionally, aperture diameter was found to influence the shape of the lens. The protrusion profile was concave at aperture diameters of 50 and 100 μm but became convex at 20 μm. At an applied voltage of 600 V, the focal length of the MLA was −0.20 mm at aperture diameters of 50 and 100 μm, representing a concave lens, but +0.05 mm at 20 μm, representing a convex lens. The MLA functioned more as a deformable lens, which transformed from a flat shape into a lens shape, than as a variable lens whose focal length changed continuously. The roles of plasticizer content, PVC chain dynamics, and aperture diameter in achieving greater control over lens curvature merit further investigation.
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