Influence of Structure Size and Geometry on Wetting Behavior of PMMA Surfaces Imprinted with Laser-Textured Stamps

In this study, the wetting behavior of micro-structured poly(methyl methacrylate) (PMMA) surfaces produced by plate-to-plate hot embossing is investigated. The embossing tools used consist of stainless steel plates, which were previously processed by different laser methods, namely Direct Laser Engraving (DLE), Direct Laser Writing (DLW) and Direct Laser Interference Patterning (DLIP). Various textures with spatial periods in the range 1.7 to 900 [micro]m and structure depths between 0.1 and 50 [micro]m were produced and successfully transferred to 175 [micro]m thick PMMA films at an embossing temperature of 130[degrees]C. In all cases, the imprints displayed the negative of the stamp textures with a difference between the stamp depth and imprint height between 6 and 16 %. The wetting behavior of the PMMA surfaces was investigated by measuring the static contact angle of distilled water as well as linseed oil. The measurements revealed an increase in the water contact angle from 79[degrees] up to 142[degrees] on the DLE-based surfaces, whereas for linseed oil, a decrease from 20[degrees] to 5[degrees] was observed for the same sample. In addition, the PMMA foils were also treated with a hydrophobizing agent in order to modify the surface chemistry. The measurements revealed no change in the water contact angle, whereas for linseed oil, contact angles up to 142[degrees] on a hierarchical surface were reached. Keywords: hot embossing, hierarchical structure, poly(methyl methacrylate), direct laser interference patterning, direct laser writing, laser engraving, wetting behavior.