Authors: Craig Priest Rossen Sedev John Ralston
Publish Date: 2012/10/03
Volume: 291, Issue: 2, Pages: 271-277
Abstract
Chemically heterogeneous surfaces are well known to induce contact angle hysteresis due to the local energy barriers that oppose contact line movement In many cases the surface heterogeneity is discontinuous ie discrete regions of different wettability exist which leads to pinning of the contact line at boundaries between regions Pinning on individual rows of microscopic defects arranged in a square lattice can be sensed using a Wilhelmy balance to reveal discrete stickslip motion For defects more wettable than the matrix with a lattice spacing of 28 μm the advancing contact line slips over ∼10 rows in a single slip step while the receding contact line stickslips between individual rows of defects Single millimetrescale defects were used to assess the energy involved when a contact line advances or recedes over a hydrophilic more wettable defect Quantitative information about defectinduced hysteresis in relation to defect dimensions is obtained The crucial importance of wetting boundaries is highlighted with an experimental example of a surface that is heterogeneous yet due to the continuously changing pattern does not exhibit contact angle hysteresis
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