Double Contact During Drop Impact on a Solid Under Reduced Air Pressure

This study was supported by King Abdullah University of Science and Technology (KAUST) under URF/1/2621-01-01. Li acknowledges the Thousand Young Talents Program of the National Natural Science Foundation of China (Grant 11621202) and Fundamental Research Funds for the Central Universities (Grant WK2090050041).Peer reviewedPublisher PD

Solution-Printed Organic Semiconductor Blends Exhibiting Transport Properties on Par with Single Crystals

Solution-printed organic semiconductors have emerged in recent years as promising contenders for roll-to-roll manufacturing of electronic and optoelectronic circuits. The stringent performance requirements for organic thin-film transistors (OTFTs) in terms of carrier mobility, switching speed, turn-on voltage and uniformity over large areas require performance currently achieved by organic single-crystal devices, but these suffer from scale-up challenges. Here we present a new method based on blade coating of a blend of conjugated small molecules and amorphous insulating polymers to produce OTFTs with consistently excellent performance characteristics (carrier mobility as high as 6.7 cm2V−1s−1, low threshold voltages of \u3c1V and low sub threshold swings \u3c0.5Vdec−1). Our findings demonstrate that careful control over phase separation and crystallization can yield solution-printed polycrystalline organic semiconductor films with transport properties and other figures of merit on par with their single-crystal counterparts

Granular jets

Worthington jets are a familiar sight in light rain upon puddles and ponds. These narrow vertical jets are formed by the radial collapse of the liquid "craters" produced by the impacting rain drops. Such jets can also be generated by super-critically forcing the standing Faraday waves on a liquid surface and have recently been cast in the formalism of physical singularities to investigate the role of the inertial focusing and the influence of surface tension on their strength. Zeff et al. propose that during the collapse of the free-surface cavity, the surface develops a curvature singularity which is dominated by inertia and surface tension, hence generating high-energy vertical jets. We have discovered that similar narrow jets occur even for granular materials, where surface tension is absent. This new phenomenon suggests that a singularity in the surface tension force is not needed to produce such jets and raises the question whether the inertial focusing is the sole mechanism. . . .published or submitted for publicationis peer reviewe

The coalescence-cascade of a drop

When a drop is deposited gently onto the surface of a layer of the same liquid, it sits momentarily before coalescing into the bottom layer. High-speed video imaging reveals that the coalescence process is not instantaneous, but rather talces place in a cascade where each step generates a smaller drop. This cascade is self-similar and we have observed up to 6 steps. The time associated with each partial coalescence scales with the surface tension time-scale. The cascade will however not proceed ad infinitum due to viscous effects, as the Reynolds number of the process is proportional to square root of drop diameter. Viscous effects will therefore begin to be important for the very smallest drops. This cascade is very similar to the one observed previously by Charles & Mason [J. Colloid Sci. 15, 236 (1960)] for two immiscible liquids, where one of the liquids replaces the air in our setup

Drag moderation by the melting of an ice surface in contact with water

We report measurements of the effects of a melting ice surface on the hydrodynamic drag of ice-shell-metal-core spheres free falling in water at a Reynolds of number Re∼2×104–3×105 and demonstrate that the melting surface induces the early onset of the drag crisis, thus reducing the hydrodynamic drag by more than 50%. Direct visualization of the flow pattern demonstrates the key role of surface melting. Our observations support the hypothesis that the drag reduction is due to the disturbance of the viscous boundary layer by the mass transfer from the melting ice surface