Using atomic scale interfaces consisting of slabs of the same materials, we study the relationship between adhesion and static friction. The work of separation, which is a measure of adhesion, and the spatial variation of the interface potential energy along the sliding direction are computed for both commensurate and incommensurate Al 2 O 3 /Al 2 O 3 interfaces, and incommensurate smooth and rough Al/ Al interfaces. These values are compared with the predicted static friction stress resulting from constant force and constant velocity molecular dynamics simulations. Simulation results show that static friction is not determined by the absolute value of adhesion. Rather, it is determined by the change of potential energy along the sliding direction.

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In this work, switchable Pickering emulsions that utilize UV/dark manipulation employ a type of smart TiO2 nanoparticle as emulsifiers. The emulsifiers can be awakened when needed via UV-induced degradation of grafted silanes on TiO2 nanoparticles. By tuning the surface wettability of TiO2 nanoparticles in situ via UV/dark actuation, emulsions stabilized by the nanoparticles can be reversibly switched between the water-in-oil (W/O) type and oil-in-water (O/W) type for several cycles. Due to the convertible wettability, the smart nanoparticle emulsifiers can be settled in either the oil phase or the water phase as desired during phase separation, making it convenient for recycling. The present work provides a facile and noninvasive method to freely manipulate the formation, breakage, and switching of the emulsion; this method has promising potential as a powerful technique for use in energy-efficient and environmentally friendly industries.

Kinetic friction during dry sliding along atomistic-scale Al͑001͒ /Al͑001͒ and ␣-Al 2 O 3 ͑0001͒/␣-Al 2 O 3 ͑0001͒ interfaces has been investigated using molecular dynamics ͑MD͒ with recently developed Reactive Force Fields ͑ReaxFF͒. It is of interest to determine if kinetic friction variations predicted with MD follow the macroscopic-scale friction laws known as Coulomb's law ͑for dry sliding͒ and Stokes' friction law ͑for lubricated sliding͒ over a wide range of sliding velocities. The effects of interfacial commensuration and roughness on kinetic friction have been studied. It is found that kinetic friction during sliding at commensurate ␣-Al 2 O 3 ͑0001͒/␣-Al 2 O 3 ͑0001͒ interfaces exceeds that due to sliding at an incommensurate ␣-Al 2 O 3 ͑0001͒/␣-Al 2 O 3 ͑0001͒ interface. For both interfaces, kinetic friction at lower sliding velocities deviates minimally from Coulombic friction, whereas at higher sliding velocities, kinetic friction follows a viscous behavior with sliding damped by thermal phonons. For atomically smooth Al͑001͒ /Al͑001͒, only viscous friction is observed. Surface roughness tends to increase kinetic friction, and adhesive transfer causes kinetic friction to increase more rapidly at higher sliding velocities.

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