Soft Condensation

TL;DR

This paper studies how droplets form and grow on soft polymer surfaces, revealing that substrate elasticity influences nucleation and that breath figures can probe polymer interface properties.

Contribution

It uncovers the role of substrate elasticity in droplet nucleation and growth, providing a new understanding of vapor flux distribution on soft surfaces.

Findings

Droplet number remains constant initially before coarsening.

Droplet nucleation is sensitive to substrate elasticity.

Breath figures can probe molecular characteristics of polymers.

Abstract

When moist air meets a cold surface, it creates a breath figure characterized by numerous small droplets. The central question is how the vapor flux is distributed between the growth of previously condensed drops and the nucleation of new ones. Here, we investigate the nucleation, growth, and coalescence of droplets on soft crosslinked polymer networks. The number of droplets initially remains constant, until drops start to coarsen according to a universal law; both phenomena are explained via the formation of a saturated boundary layer. Although nucleation occurs at a scale where the polymer network resembles a melt, we quantitatively unveil an algebraic sensitivity of the number of droplets on the substrate elasticity. Our findings suggest that nucleation follows a surprisingly low-energy pathway, influenced by the degree of crosslinking. Consequently, breath figures offer a macroscopic approach to probe the molecular characteristics of the polymer interface.