Enhanced Condensation on Soft Materials through Bulk Lubricant Infusion

Abstract

Soft substrates enhance droplet nucleation during water vapor condensation because their deformability inherently reduces the energetic threshold for heterogeneous nucleation relative to rigid substrates. However, this enhancement is counteracted later in the condensation cycle, when substrate viscoelastic dissipation inhibits condensate droplet shedding. Here a polydimethylsiloxane (PDMS) based organogel is designed to overcome this limitation. It is shown that merely 5% bulk lubricant infusion in PDMS reduces viscoelastic dissipation in the substrate by nearly 28 times while doubling the droplet nucleation density. Parameters for water condensation on this organogel are correlated with material properties controlled by design, i.e., fraction and composition of uncrosslinked chains and shear modulus. It is demonstrated that the increase in nucleation density and reduction in precoalescence droplet growth rate is rather insensitive to the lubricant percentage in PDMS within the broad range investigated. These results indicate the presence of a lubricant layer on the substrate surface that cloaks the growing condensate droplets. This cloaking effect is visualized, and it is shown that cloaking occurs significantly faster on PDMS if it is infused with bulk lubricant. Overall, bulk lubricant infusion in PDMS enhances condensation and leads to a more than 40% higher dewing on the substrate.

Superhydrophobic microstructures for better anti-icing performances: open-cell or closed-cell?

“…[49][50][51] When the surface temperature falls below the dew point, water vapor in the air tends to condense into liquid droplets, which eventually freeze after the surface temperature decreases to subzero. 52 The frozen droplets connect by ice bridges, forming condensation frosts. Once the condensation frosts on superhydrophobic surfaces are not effectively inhibited, the superhydrophobicity and anti-icing properties of surfaces will be greatly degraded owing to the high affinity of frost to water.…”

Quantification of Nucleation Site Density as a Function of Surface Wettability on Smooth Surfaces

“…Liquid infused surfaces (LIS) have been shown to enhance droplet mobility in condensation applications, by dramatically reducing contact angle hysteresis, however the gradual loss of lubricant could make the effect short lived. [31,[36][37][38][39] Polymer infused porous surfaces also offer low contact angle hysteresis and tunability, as well as being more robust than LIS, however they are complex to fabricate and may be challenging to scale up. [37] Only recently, Cha et al have shown that a less complex hydrophilic surface with low contact angle hysteresis, can determine efficient dropwise condensation.…”

Spontaneous Charging of Drops on Lubricant-Infused Surfaces

“…In case of LIS, the wetted surface is liquid rather than solid. Usually, LIS consist of a structured surface that is impregnated with a lubricant. − These surfaces have attracted much attention because they provide low sliding angles. Water drops start sliding down inclined LIS even at low tilt angles.…”