Using Amphiphilic Nanostructures To Enable Long-Range Ensemble Coalescence and Surface Rejuvenation in Dropwise Condensation

Abstract

Controlling coalescence events in a heterogeneous ensemble of condensing droplets on a surface is an outstanding fundamental challenge in surface and interfacial sciences, with a broad practical importance in applications ranging from thermal management of high-performance electronic devices to moisture management in high-humidity environments. Nature-inspired superhydrophobic surfaces have been actively explored to enhance heat and mass transfer rates by achieving favorable dynamics during dropwise condensation; however, the effectiveness of such chemically homogeneous surfaces has been limited because condensing droplets tend to form as pinned Wenzel drops rather than mobile Cassie ones. Here, we introduce an amphiphilic nanostructured surface, consisting of a hydrophilic base with hydrophobic tips, which promotes the periodic regeneration of nucleation sites for small droplets, thus rendering the surface self-rejuvenating. This unique amphiphilic nanointerface generates an arrangement of condensed Wenzel droplets that are fluidically linked by a wetted sublayer, promoting previously unobserved coalescence events where numerous droplets simultaneously merge, without direct contact. Such ensemble coalescences rapidly create fresh nucleation sites, thereby shifting the overall population toward smaller droplets and enhancing the rates of mass and heat transfer during condensation.

Mimicking Bubble Use in Nature: Propulsion of Janus Particles due to Hydrophobic‐Hydrophilic Interactions

“…Another interesting aspect is the influence of surfaces with varying interfacial adhesion on the nucleation of bubbles and the propulsion of particle‐bubble complexes. As it was previously shown, these structures can change completely the hydrophilic‐hydrophobic interactions and the behavior of water droplets on them . The synthesis method of the Janus particles presented in this article can be potentially used for other particle geometries and is complimentary to embedding and patterning of particles and capsules in biocompatible films, where the degree of patterning can be controlled by gold nanoparticles adsorbed on such films …”

Condensation heat transfer on superhydrophobic surfaces

“…Controlling nucleation has been investigated, but has primarily focused on patterning surface chemistry heterogeneities [56][57][58][59][60][61][62] (hybrid hydrophobic/hydrophilic surfaces) at the length scale of the structures or larger to simultaneously increase the nucleation rate (hydrophilic spots) and achieve high droplet mobility (hydrophobic spots). Although spatial control of nucleation has been demonstrated 58 , it was also accompanied by higher droplet adhesion 63 .…”

Time-averaged droplet size distribution in steady-state dropwise condensation

“…A remarkable case is dropwise condensation, i.e., water vapor condenses into droplets on substrates [6][7][8][9][10][11]. It has long been an engineering concern due to higher heat transfer coefficients in dropwise condensation than that in filmwise condensation [12].…”