Control of Contact Angle on Soft Material Surface with Deformable Micro Structures

Abstract

Interfacial free energy of materials and micro structures on solid surface influence wetting behavior at solid-liquid interface. Controls of wettability by making constant-shaped micro surface structures have been approached. By reference to those approaches, the authors consider that deformation of micro surface structures changes wettability. In this report, we prepared a micropillar array on a silicone rubber sheet. The diameter and the height of pillars were 10 μm or 200 μm. A water droplet of volume 5 μL was dropped on the micropillar array. Pitches of pillars increased as the rubber sheet was extended, and contact angle of the droplet decreased. Pitches decreased as the sheet was contracted, and the contact angle increased. The contact line of water droplet jumped from exterior pillars to interior pillars when pitches increased. This contact angle change will contribute to surface-improvement of soft actuators.