Mapping Depletion of Lubricant Films on Antibiofouling Wrinkled Slippery Surfaces

Slippery
liquid infused porous surfaces (SLIPS) have recently gained
a lot of attention because of their wide range of applications. We
recently showed that SLIPS with most of their surface depleted of
lubricant, as little lubricant as 0.02 ± 0.01 μL cm–1, were effective against marine biofouling. Characterization
of the depletion and configuration of the immobilized liquid layer
on SLIPS is crucial to optimizing their performance. Previous attempts
at mapping lubricant thickness have been diffraction limited or indirectly
measured thickness. Here, we use atomic force microscopy meniscus
force measurements to directly map lubricant thickness with nanoscale
resolution on wrinkled surfaces made from Teflon and poly­(4-vinylpyridine)
(P4VP). Using this method, we show that SLIPS are easily depleted
and are effectively heterogeneous surfaces, where the majority of
the surface is a thick lubricating layer stabilized by capillary forces
and part nanothin layer stabilized long-range intermolecular forces.
We found that the depleted silicone oil thickness on the tops of nonwettable
(Teflon) wrinkles is approx. 5 nm, close to but greater than the minimum
measurable thickness of approx. 3 nm. The silicone oil thickness on
the tops of wettable (P4VP) wrinkles is approx. 15 nm. Surfaces in
this state still show antibiofouling properties and thus show that
a thick lubricating layer is not necessary for all favorable properties
of SLIPS.