A morphological study on direct polymer cast micro-textured hydrophobic surfaces

The surface microstructures that contribute to the lotus leaf's superhydrophobicity are replicated onto a polymer surface using a two-stage (negative-positive) direct casting method and the replicates' surface morphology is investigated in this study. Vinyl polysiloxane (VPS), polydimethylsiloxane (PDMS) and polymethylmethacrylate (PMMA) are used for the replication and the replicates obtained are investigated using confocal microscopy, scanning electron microscopy (SEM), and contact angle measurements. Geometric texture parameters such as peak height, peak/valley base width and inter-spacing between adjacent peak/valleys are measured for the lotus leaf and its replicates. Of the six combinations of positive and negative replicates attempted, VPS-PMMA and PDMS-PMMA replicates display shorter peak heights and larger base widths. These replicates have contact angles of 132.1° and 129.2° respectively, which are closest to the contact angle of the lotus leaf, 152.9°. Statistical two sample t-test revealed that VPS-PMMA's surface morphological parameters are closest to that of the lotus leaf. Also, theoretical calculations, based on two different methods from literature, using the measured geometric texture parameters show that polymer replicates satisfy criteria for a stable Cassie-Baxter wetting regime.