Enhancing condensation on soft substrates through bulk lubricant infusion

TL;DR

This study demonstrates that bulk lubricant infusion in soft PDMS substrates significantly enhances water vapor condensation by increasing nucleation density, reducing droplet growth, and improving dewing, through decreased viscoelastic dissipation and a cloaking lubricant layer.

Contribution

The paper introduces a novel approach of bulk lubricant infusion in soft substrates to improve condensation performance by reducing viscoelastic dissipation and promoting droplet cloaking.

Findings

Bulk lubricant infusion reduces viscoelastic dissipation by over 30 times.

Nucleation density more than doubles with lubricant infusion.

Over 40% increase in dewing observed due to enhanced condensation.

Abstract

Soft substrates such as polydimethylsiloxane (PDMS) enhance droplet nucleation during the condensation of water vapour, because their deformability inherently reduces the energetic threshold for heterogeneous nucleation relative to rigid substrates. However, this enhanced droplet nucleation is counteracted later in the condensation cycle, when the viscoelastic dissipation inhibits condensate droplet shedding from the substrate. Here, we show that bulk lubricant infusion in the soft substrate is a potential pathway for overcoming this limitation. We demonstrate that even 5% bulk lubricant infusion in PDMS reduces viscoelastic dissipation in the substrate by more than 30 times and more than doubles the droplet nucleation density. We correlate the droplet nucleation and growth rate with the material properties controlled by design, i.e. the fraction and composition of uncrosslinked chains, shear modulus, and viscoelastic dissipation. Through in-situ, microscale condensation on the substrates, we show that the increase in nucleation density and reduction in pre-coalescence droplet growth rate is insensitive to the percentage of lubricant in PDMS. Our results indicate the presence of a lubricant layer on the substrate surface that cloaks the growing condensate droplets. We visualize the cloaking effect and show that lubricant infusion in PDMS significantly increases the rate of cloaking compared to PDMS without any lubricant infusion. Finally, we show that the overall enhanced condensation due to bulk lubricant infusion in PDMS leads to more than 40% increase in dewing on the substrate.