Long-Lasting Superhydrophilic Polymers via Multiscale Topographies

The challenge in achieving extreme wetting (<10° contact angle) in engineering polymer surfaces lies in the balance between water-loving chemical compositions and the degrading effects of absorbed water on physical, thermal, and mechanical properties. Hydrophobic recovery caused by surface energy minimization and surface polymer chain relaxation also contributes to the challenges in achieving stable extreme wetting in thermoplastic polymers. In this report, multiscale topography consisting of random nanoporous structure and uniform micropattern presents an extended capillary network to achieve superwetting on thermoplastic polymers. The topography that results in a buried pore structure achieves two design objectives: (1) an extended surface area that is shielded from surface contamination by the small pore size and tortuous path into the coating thickness and (2) an extended path for wicking of liquid into the coating to achieve long-lasting superhydrophilic performance. Nanoporous poly(methyl methacrylate) (PMMA) coatings on microtextured substrates exhibit superhydrophilic performance through a two-phase contact angle decline. Nanoporous PMMA on 1 μm grating and 500 nm pillar arrays yielded the best and most robust superhydrophilic wetting with a measured water contact angle of near 0°, a complete spreading state over a test period of 48 h and over multiple rewetting tests.