Adaptive fluid-infused porous films with tunable transparency and wettability

TLDR: It is shown that a graded mechanical stimulus can be directly translated into finely tuned, dynamic adjustments of optical transparency and wettability and should make possible the rational design of tunable, multifunctional adaptive materials for a broad range of applications.

Abstract: Materials that adapt dynamically to environmental changes are currently limited to two-state switching of single properties, and only a small number of strategies that may lead to materials with continuously adjustable characteristics have been reported. Here we introduce adaptive surfaces made of a liquid film supported by a nanoporous elastic substrate. As the substrate deforms, the liquid flows within the pores, causing the smooth and defect-free surface to roughen through a continuous range of topographies. We show that a graded mechanical stimulus can be directly translated into finely tuned, dynamic adjustments of optical transparency and wettability. In particular, we demonstrate simultaneous control of the film's transparency and its ability to continuously manipulate various low-surface-tension droplets from free-sliding to pinned. This strategy should make possible the rational design of tunable, multifunctional adaptive materials for a broad range of applications.

Figures

Figure 3 Dynamic control of droplet mobility. (a) Scheme showing the control mechanism: a droplet of test liquid changes from sliding to pinning under external stimuli (for example, mechanical stretch) as the film surface reconfigures from flat to rough. (b) Demonstration of the control of oil mobility on the dynamic slippery surface under stretch. A drop of silicone oil (6 μL, γ=~20.4 mN/m) was deposited on a tilted surface, sliding down (i-iii) until a strain of 6 % was applied (iv). A second oil drop deposited on the stretched surface was also pinned (v). Both drops slid down when the strain was relaxed (vi-viii). (c) Comparison of sliding angle (silicone oil) as a function of strain on the PDMS substrate with different amounts of infused lubricant. (d) Tuning the oil sliding angle as a function of strain for test droplets of different interfacial tensions. Perfluoro-lubricant (Krytox 103) with a unit amount of 3.0 μL/cm2 was used as the infused fluid.