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When neutral water drops impact and rebound from superhydrophobic surfaces, they acquire a positive electrical charge. To measure the charge, we analyzed the trajectory of rebounding drops in an external...

Enhancing heat transfer efficiency by liquid condensation plays a critical role in recovering and utilizing low‐grade heat. However, overall heat transfer efficiency is commonly limited by the inefficient vapor–liquid phase transition flux and enthalpy during liquid condensation. Here, we report that by introducing small amount of water into the phase‐change process of ethanol on a liquid‐like polydimethylsiloxane (PDMS) brush surface, the heat transfer coefficient is significantly enhanced, in particular, by more than one order of magnitude compared to the pure ethanol condensation. Such enhanced thermal performance is primarily due to the elaborate balance between promoting condensation, that is, nucleation and growth, and increasing latent heat by regulating components of water and ethanol, as well as the rapid droplet removal by condensing on the PDMS brushes. Note that the more stabilized dropwise condensation of the binary liquids, retained by accelerating the droplet coalescence velocity, beyond filmwise condensation ensures its significant effectivity under high heat flux.

Chitosan is a useful and versatile biopolymer with several industrial and biological applications. Whereas its physical and physicochemical bulk properties have been explored quite intensively in the past, there is a lack of studies regarding the morphology and growth mechanisms of thin films of this biopolymer. Of particular interest for applications in bionanotechnology are ultrathin films with thicknesses under 500 Å. Here, we present a study of thin chitosan films prepared in a dry process using physical vapor deposition and in situ ellipsometric monitoring. The prepared films were analyzed with atomic force microscopy in order to correlate surface morphology with evaporation parameters. We find that the surface morphology of our final thin films depends on both the optical thickness, i.e., measured with ellipsometry, and the deposition rate. Our work shows that ultrathin biopolymer films can undergo dewetting during film formation, even in the absence of solvents and thermal annealing.

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