We introduce and present the fundamentals of stress-localization concept to minimize adhesion of ice or other contaminants on a surface.

No abstract

Evaporation is a fundamental and core phenomenon in a broad range of disciplines including power generation and refrigeration systems, desalination, electronic/photonic cooling, aviation systems, and even biosciences. Despite its importance, the current theories on evaporation suffer from fitting coefficients with reported values varying in a few orders of magnitude. Lack of a sound model impedes simulation and prediction of characteristics of many systems in these disciplines. Here, we studied evaporation at a planar liquid-vapor interface through a custom-designed, controlled, and automated experimental setup. This experimental setup provides the ability to accurately probe thermodynamic properties in vapor, liquid, and close to the liquid-vapor interface. Through analysis of these thermodynamic properties in a wide range of evaporation mass fluxes, we cast a predictive model of evaporation based on nonequilibrium thermodynamics with no fitting parameters. In this model, only the interfacial temperatures of liquid and vapor phases along with the vapor pressure are needed to predict evaporation mass flux. The model was validated by the reported study of an independent research group. The developed model provides a foundation for all liquid-vapor phase change studies including energy, water, and biological systems.

Advancement in high-performance photonics/electronics devices has boosted generated thermal energy, making thermal management a bottleneck for accelerated innovation in these disciplines. Although various methods have been used to tackle the thermal management problem, evaporation with nanometer fluid thickness is one of the most promising approaches for future technological demands. Here, we studied thin-film evaporation in nanochannels under absolute negative pressure in both transient and steady-state conditions. We demonstrated that thin-film evaporation in nanochannels can be a bubble-free process even at temperatures higher than boiling temperature, providing high reliability in thermal management systems. To achieve this bubble-free characteristic, the dimension of nanochannels should be smaller than the critical nucleolus dimension. In transient evaporative conditions, there is a plateau in the velocity of liquid in the nanochannels, which limits the evaporative heat flux. This limit is imposed by liquid viscous dissipation in the moving evaporative meniscus. In contrast, in steady-state condition, unprecedented average interfacial heat flux of 11 ± 2 kW cm–2 is achieved in the nanochannels, which corresponds to liquid velocity of 0.204 m s–1. This ultrahigh heat flux is demonstrated for a long period of time. The vapor outward transport from the interface is both advective and diffusion controlled. The momentum transport of liquid to the interface is the limiting physics of evaporation at steady state. The developed concept and platform provide a rational route to design thermal management technologies for high-performance electronic systems.

Recently, intensive research has been conducted on the development of bacterial repelling surfaces because of the disadvantages of the conventional bactericidal leaching and contact-killing surfaces for practical application. Among these bacteriarepelling methodologies, zwitterionic polymers were widely investigated because of its excellent nonfouling properties, but its durability has limited its widespread use since most of the surfaces were developed by constructing polymer brushes via atom transfer radical polymerization (ATRP). In this study, we developed zwitterionic polymer surfaces with desirable mechanical and chemical durability for long-term use through simple blending of poly(sulfobetaine methacrylate) (PSBMA)/poly(ether sulfone) (PES) semi-interpenetrated networked microgels with hydrophobic PES polymer matrix. Results show that the as-prepared surfaces can efficiently induce hydration layers and, thus, reduce the bacterial attachment through resisting nonspecific protein adsorption. The bacterial adhesion for Escherichia coli and Staphylococcus aureus was investigated under both flow and static conditions. This work has set a paradigm for developing durable antibacterial surfaces with nonfouling properties.

Functional surfaces are of paramount engineering importance for various applications. The purpose of this review is to present counter-intuitive methods of fabrication based upon damage or instabilities for creating value-added surface functions.

Growing demands for bio-friendly antifouling surfaces have stimulated the development of new and ever-improving material paradigms.

Evaporative mass flux is governed by interfacial state of liquid and vapor phases. For closely similar pressures and mass fluxes of liquid water into its own vapor, discontinuity between interfacial liquid and vapor temperatures in the range of 0.14-28 K is reported. This controversial discontinuity has resulted in an obstacle on understanding and theoretical modeling of evaporation. Here, through study of vapor transport by Boltzmann transport equation solved through Direct Simulation Monte Carlo Method, we demonstrated that the measured discontinuities were strongly affected by boundary condition on the vapor side of the interface and do not reflect the interfacial state. The temperature discontinuity across the evaporating interface is ≤ 0.1 K for all these studies. To accurately capture the interfacial state, the vapor heat flux should be suppressed.