Stable Wettability Control of Nanoporous Microstructures by iCVD Coating of Carbon Nanotubes

Scalable
manufacturing of structured materials with engineered nanoporosity
is critical for applications in energy storage devices (i.e., batteries
and supercapacitors) and in the wettability control of surfaces (i.e.,
superhydrophobic and superomniphobic surfaces). Patterns formed in
arrays of vertically aligned carbon nanotubes (VA-CNTs) have been
extensively studied for these applications. However, the as-deposited
features are often undesirably altered upon liquid infiltration and
evaporation because of capillarity-driven aggregation of low density
CNT forests. Here, it is shown that an ultrathin, conformal, and low-surface-energy
layer of poly perfluorodecyl acrylate, poly­(1H,1H,2H,2H-perfluorodecyl
acrylate) (pPFDA), makes the VA-CNTs robust against surface-tension-driven
aggregation and densification. This single vapor-deposition step allows
the fidelity of the as-deposited VA-CNT patterns to be retained during
wet processing, such as inking, and subsequent drying. It is demonstrated
how to establish omniphobicity or liquid infiltration by controlling
the surface morphology. Retaining a crust of entangled CNTs and pPFDA
aggregates on top of the patterned VA-CNTs produces micropillars with
re-entrant features that prevent the infiltration of low-surface-tension
liquids and thus gives rise to stable omniphobicity. Plasma treatments
before and after polymer deposition remove the crust of entangled
CNTs and pPFDA aggregates and attach hydroxyl groups to the CNT tips,
enabling liquid infiltration yet preventing densification of the highly
porous CNTs. The latter observation demonstrates the protective character
of the pPFDA coating with the potential application of these surfaces
for direct contact printing of microelectronic features.