Azimuthal variation of apparent contact angles on structured surfaces featuring micrometric ramps, pyramids and staggered cubes at two different inherent wettabilities

TL;DR

This study investigates how microstructured surfaces with different geometries and wettability treatments influence the azimuthal variation of apparent contact angles, revealing structure-dependent pinning effects and anisotropic wetting behaviors.

Contribution

It introduces a manufacturing process for microstructured PMMA surfaces and systematically analyzes how structure geometry and surface treatment affect contact angle variation.

Findings

All structures cause azimuthal contact angle variation.

Pinning at ramp tops enhances contact angles on one side.

Pyramid and cube structures show orientation-dependent pinning effects.

Abstract

As new manufacturing methods enable manufacturing of microstructured surfaces with varying structure geometries, questions remain on some effects on the wetting behavior and the resulting apparent contact angles. In this study, we report the manufacturing process using 3D Direct Laser Writing (3D-DLW) and hot embossing for Poly-methylmethacrylate (PMMA) surfaces with micrometric pyramids, cubes on a staggered grid and two types of ramped structures. We measure the azimuthal variation of the apparent contact angle of sessile droplets on the surfaces. Using plasma polymerization or no treatment of the surfaces, two different inherent wettabilities are studied. We find that while all structure types cause an azimuthal variation of the apparent contact angle, pinning at the ramp tops increases the contact angle more strongly on one side. On pyramid structures, pinning lines can occur on the structure axes and diagonals similarly. For cubes on a hexagonal grid, the strongest contact angle increases are observed along the primary structure axes, where pinning is preferred while smaller peaks are seen on the secondary axes at 60{\deg} and 120{\deg} to the primary axis.