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Interactions between proteins lie at the heart of numerous biological processes and are essential for the proper functioning of the cell. Although the importance of hydrophobic residues in driving protein interactions is universally accepted, a characterization of protein hydrophobicity, which informs its interactions, has remained elusive. The challenge lies in capturing the collective response of the protein hydration waters to the nanoscale chemical and topographical protein patterns, which determine protein hydrophobicity. To address this challenge, here, we employ specialized molecular simulations wherein water molecules are systematically displaced from the protein hydration shell; by identifying protein regions that relinquish their waters more readily than others, we are then able to uncover the most hydrophobic protein patches. Surprisingly, such patches contain a large fraction of polar/charged atoms and have chemical compositions that are similar to the more hydrophilic protein patches. Importantly, we also find a striking correspondence between the most hydrophobic protein patches and regions that mediate protein interactions. Our work thus establishes a computational framework for characterizing the emergent hydrophobicity of amphiphilic solutes, such as proteins, which display nanoscale heterogeneity, and for uncovering their interaction interfaces.

A self‐confined solid‐state dewetting mechanism is reported that can fundamentally reduce the use of sophisticated nanofabrication techniques, enabling efficient wafer‐scale patterning of non‐closely packed (ncp) gold nanoparticle arrays. When combined with a soft lithography process, this approach can address the reproducibility challenges associated with colloidal crystal self‐assembly, allowing for the batch fabrication of ncp gold arrays with consistent ordering and even optical properties. The resulting dewetted ncp gold nanoparticle arrays exhibit strong surface lattice resonance properties when excited in inhomogeneous environments under normal white‐light incidence. With these SLR properties, the sensitive plasmonic sensing of molecular interactions is achieved using a simple transmission setup. This study will advance the development of miniaturized and portable devices. A self‐confined solid‐state dewetting mechanism is proposed that can fundamentally avoid the use of sophisticated nanofabrication techniques and achieve the wafer‐scale patterning of ncp gold nanoparticle arrays simply and efficiently. The dewetted ncp gold nanoparticle arrays demonstrate non‐polarized white‐light‐excited surface lattice resonance properties in asymmetric environments, which are suitable for plasmonic sensing applications.

We present a method to control the interfacial tension of a liquid alloy of gallium via electrochemical deposition (or removal) of the oxide layer on its surface. In sharp contrast with conventional surfactants, this method provides unprecedented lowering of surface tension (∼500 mJ/m ² to near zero) using very low voltage, and the change is completely reversible. This dramatic change in the interfacial tension enables a variety of electrohydrodynamic phenomena. The ability to manipulate the interfacial properties of the metal promises rich opportunities in shape-reconfigurable metallic components in electronic, electromagnetic, and microfluidic devices without the use of toxic mercury. This work suggests that the wetting properties of surface oxides—which are ubiquitous on most metals and semiconductors—are intrinsic “surfactants.” The inherent asymmetric nature of the surface coupled with the ability to actively manipulate its energetics is expected to have important applications in electrohydrodynamics, composites, and melt processing of oxide-forming materials. Significance We present a method to control the interfacial energy of a liquid metal via electrochemical deposition (or removal) of an oxide layer on its surface. Unlike conventional surfactants, this approach can tune the interfacial tension of a metal significantly (from ∼7× that of water to near zero), rapidly, and reversibly using only modest voltages. These properties can be harnessed to induce previously unidentified electrohydrodynamic phenomena for manipulating liquid metal alloys based on gallium, which may enable shape-reconfigurable metallic components in electronic, electromagnetic, and microfluidic devices without the use of toxic mercury. The results also suggest that oxides—which are ubiquitous on most metals and semiconductors—may be harnessed to lower interfacial energy between dissimilar materials.

Superrepellency is an extreme situation where liquids stay at the tops of rough surfaces, in the so-called Cassie state. Owing to the dramatic reduction of solid/liquid contact, such states lead to many applications, such as antifouling, droplet manipulation, hydrodynamic slip, and self-cleaning. However, superrepellency is often destroyed by impalement transitions triggered by environmental disturbances whereas inverse transitions are not observed without energy input. Here we show through controlled experiments the existence of a “monostable” region in the phase space of surface chemistry and roughness, where transitions from Cassie to (impaled) Wenzel states become spontaneously reversible. We establish the condition for observing monostability, which might guide further design and engineering of robust superrepellent materials.

In this paper, two-step sequential spin-dip and spin-spin coating, as well as one-step spin coating, methods are used to fabricate methylammonium lead mixed-halide perovskites to study the effect of process parameters, including the choice of the solvent, annealing temperature, spin velocity, and dipping time on the characteristics of the perovskite film. Our results show that using a mixture of DMF and DMSO, with volume ratio of 1:1, as the organic solvents for PbCl 2 results in the best mixed-halide perovskite because of the effective coordination between DMSO and PbCl 2 . Surface dewetting due to two effects, i.e., crystallization and thin liquid film instability, is observed and discussed, where an intermediate spin velocity of about 4000 rpm is found suitable to suppress dewetting. The perovskite film fabricated using the one-step method followed by anti-solvent treatment shows the best perovskite conversion in XRD patterns, and the planar device fabricated using the same method exhibited the highest efficiency among the employed methods. The perovskite layer made by sequential spin-dip coating is found thicker with higher absorbance, but the device shows a lower efficiency because of the challenges associated with perovskite conversion in the sequential method. The one-step deposition method is found easier to control and more promising than the sequential deposition methods.

The problem of simulating solid-state dewetting of thin films in three dimensions (3D) by using a sharp-interface approach is considered in this paper. Based on the thermodynamic variation, a speed method is used for calculating the first variation to the total surface energy functional. The speed method shares more advantages than the traditional use of parameterized curves (or surfaces); e.g., it is more intrinsic, and its variational structure (related with the Cahn-Hoffman ξ-vector) is clearer. By making use of the first variation, necessary conditions for the equilibrium shape of the solid-state dewetting problem are given, and a kinetic sharp-interface model which includes the surface energy anisotropy is also proposed. This sharp-interface model describes the interface evolution in 3D which occurs through surface diffusion and contact line migration. By solving the proposed model, we perform numerical simulations to investigate the evolution of patterned films, e.g., the evolution of a cuboid and pinch-off of a long cuboid. Numerical simulations in 3D demonstrate the performance of the sharp-interface approach to capture many of the complexities observed in solid-state dewetting experiments.

Thin polymer films on hydrophobic substrates are susceptible to rupture and hole formation. This, in turn, initiates a complex dewetting process, which ultimately leads to characteristic droplet patterns. Experimental and theoretical studies suggest that the type of droplet pattern depends on the specific interfacial condition between the polymer and the substrate. Predicting the morphological evolution over long timescales and on the different length scales involved is a major computational challenge. In this study, a highly adaptive numerical scheme is presented, which allows for following the dewetting process deep into the nonlinear regime of the model equations and captures the complex dynamics, including the shedding of droplets. In addition, our numerical results predict the previously unknown shedding of satellite droplets during the destabilization of liquid ridges that form during the late stages of the dewetting process. While the formation of satellite droplets is well known in the context of elongating fluid filaments and jets, we show here that, for dewetting liquid ridges, this property can be dramatically altered by the interfacial condition between polymer and substrate, namely slip. This work shows how dissipative processes can be used to systematically tune the formation of patterns.

Rough or textured hydrophobic surfaces are dubbed “superhydrophobic” due to their numerous desirable properties, such as water repellency and interfacial slip. Superhydrophobicity stems from an aversion of water for the hydrophobic surface texture, so that a water droplet in the superhydrophobic “Cassie state” contacts only the tips of the rough surface. However, superhydrophobicity is remarkably fragile and can break down due to the wetting of the surface texture to yield the “Wenzel state” under various conditions, such as elevated pressures or droplet impact. Moreover, due to large energetic barriers that impede the reverse transition (dewetting), this breakdown in superhydrophobicity is widely believed to be irreversible. Using molecular simulations in conjunction with enhanced sampling techniques, here we show that on surfaces with nanoscale texture, water density fluctuations can lead to a reduction in the free energetic barriers to dewetting by circumventing the classical dewetting pathways. In particular, the fluctuation-mediated dewetting pathway involves a number of transitions between distinct dewetted morphologies, with each transition lowering the resistance to dewetting. Importantly, an understanding of the mechanistic pathways to dewetting and their dependence on pressure allows us to augment the surface texture design, so that the barriers to dewetting are eliminated altogether and the Wenzel state becomes unstable at ambient conditions. Such robust surfaces, which defy classical expectations and can spontaneously recover their superhydrophobicity, could have widespread importance, from underwater operation to phase-change heat transfer applications.

A common approach to test electrocatalyst nanoparticles (NPs) for electrolyzers and fuel cells is to deposit catalyst particles (e.g., Pt/carbon) onto standard disk electrodes (e.g., glassy carbon) by making use of inks based on binders (ionomers such as Nafion). In recent years, physical and chemical vapor deposition have garnered interest to deposit catalyst films or particles on electrode surfaces, to circumvent the complications associated with the use of inks. Samples prepared this way might be incompatible with standard equipment, e.g., rotating disk electrodes (RDEs) to assess the effect of mass transport on the electrode performance. Herein, a custom‐built adapter is presented to test samples prepared by physical deposition methods in a RDE setup. Using an outer‐sphere redox probe (K4Fe(CN)6), it is demonstrated that the custom‐built adapter provides mass transport conditions comparable to those obtained with a standard disk electrode in a classic RDE setup. Theadapter is used to investigate the hydrogen evolution reaction (HER) activity of model Pt electrodes, that is, sputter‐deposited Pt thin films and thermally “dewetted” Pt NPs, in acid electrolytes. Under both hydrostatic and hydrodynamic conditions, the Pt NPs show significantly higher HER kinetics compared to Pt thin films. The results indicate that the enhanced HER activity observed for dewetted Pt NPs is intrinsic and of a kinetic nature, likely linked to catalyst/support interactions, and is not a consequence of mass transport effects. A rotating‐disk‐electrode adapter is designed to investigate non‐standard‐disk‐electrodes under defined mass transport conditions. The hydrogen evolution performance of model Pt film versus thermally dewetted Pt nanoparticle (NP) electrodes is tested. Dewetted NPs are significantly more active than films under both static and hydrodynamic conditions. Their higher activity is of a kinetic nature and is proposed to arise from metal–support interactions.