  We designed spongy monoliths allowing liquid delivery to their surfaces
through continuous nanopore systems (mean pore diameter ca. 40 nm). These
nanoporous monoliths were flat or patterned with microspherical structures a
few 10 microns in diameter, and their surfaces consisted of aprotic polymer or
of TiO2 coatings. Liquid may reduce adhesion forces FAd; possible reasons
include screening of solid-solid interactions and poroelastic effects.
Softening-induced deformation of flat polymeric monoliths upon contact
formation in the presence of liquids enhanced the work of separation WSe. On
flat TiO2-coated monoliths, WSe was under wet conditions smaller than under dry
conditions, possibly because of liquid-induced screening of solid-solid
interactions. Under dry conditions, WSe is larger on flat TiO2-coated monoliths
than on flat monoliths with polymeric surface. However, under wet conditions
liquid-induced softening results in larger WSe on flat monoliths with polymeric
surface than on flat monoliths with oxidic surface. Monolithic microsphere
arrays show anti-adhesive properties; FAd and WSe are reduced by at least one
order of magnitude as compared to flat nanoporous counterparts. On nanoporous
monolithic microsphere arrays, capillarity (WSe is larger under wet than under
dry conditions) and solid-solid interactions (WSe is larger on oxide than on
polymer) dominate contact mechanics. Thus, the microsphere topography reduces
the impact of softening-induced surface deformation and screening of
solid-solid interactions associated with liquid supply. Overall, simple
modifications of surface topography and chemistry combined with delivery of
liquid to the contact interface allow adjusting WSe and FAd over at least one
order of magnitude. (...)
