Deformable polyvinyl chloride gel for fabrication of varifocal microlens array

• Published in: Engineering Research Express Vol. 2; no. 4; pp. 45017 - 45026
• Main Authors: Yamada, Yasumi, Emori, Hideyuki, Hirai, Toshihiro
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.12.2020
• Subjects: actuator; deformable lens; lens; microlensarray; PVC; varifocal lens
• ISSN: 2631-8695; 2631-8695
• DOI: 10.1088/2631-8695/abc186

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 m 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 m but became convex at 20 m. At an applied voltage of 600 V, the focal length of the MLA was −0.20 mm at aperture diameters of 50 and 100 m, representing a concave lens, but +0.05 mm at 20 m, 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.