Chemistry Letters, Vol.41, No.10, 1343-1345, 2012
Pinning-induced Variations of the Contact Angle of Drops on Microstructured Surfaces
The shape of droplets placed on a microstructured pillar surface is investigated by laser scanning confocal microscopy, LSCM. The microstructure consists of cylindrical pillars arranged in a square lattice. Using LSCM the three-dimensional shape of drops and the contact angle are imaged above and between neighboring pillars. Pinning of liquid at the three-phase contact line prevents mm-sized drops to reach their global equilibrium profile. Pinning is observed along the main and diagonal axes of the quadratically arranged pillars. If the preferred orientation of pinning changes, the contact angle can vary by almost 20 between neighboring pillars. Periodic variations of the contact angle are observed along the contact line. The contact angle is determined by the local constraints set by the Young's equation and large scale constraints set by the Laplace pressure.