Self-propelling surfactant droplets in chemically-confined microfluidics – cargo transport, drop-splitting and trajectory control

We demonstrate the applicability of self-propulsion as a passive driving mechanism for droplets in chemically-confined microfluidics. The droplets can be used to transport considerably sized solid cargo particles. We implemented thermal actuation as a steering mechanism for the droplets at fluidic junctions

Droplet actuation induced by coalescence: experimental evidences and phenomenological modeling

This paper considers the interaction between two droplets placed on a substrate in immediate vicinity. We show here that when the two droplets are of different fluids and especially when one of the droplet is highly volatile, a wealth of fascinating phenomena can be observed. In particular, the interaction may result in the actuation of the droplet system, i.e. its displacement over a finite length. In order to control this displacement, we consider droplets confined on a hydrophilic stripe created by plasma-treating a PDMS substrate. This controlled actuation opens up unexplored opportunities in the field of microfluidics. In order to explain the observed actuation phenomenon, we propose a simple phenomenological model based on Newton's second law and a simple balance between the driving force arising from surface energy gradients and the viscous resistive force. This simple model is able to reproduce qualitatively and quantitatively the observed droplet dynamics

Oblique roughness replication in strained SiGe/Si multilayers

The replication of the interface roughness in SiGe/Si multilayers grown on miscut Si(001) substrates has been studied by means of x-ray reflectivity reciprocal space mapping. The interface profiles were found to be highly correlated and the direction of the maximal replication was inclined with respect to the growth direction. This oblique replication is explained by the influence of the inhomogeneous strain distribution around step bunches. The formation of step bunches is described by a kinetic step-flow model based on the work by Tersoff et al. [Phys. Rev. Lett. 75, 2730 (1995)]. We have generalized this model by taking into account local variations of the in-plane strain. The angle of obliqueness deduced from these calculations agrees very well with the experimental findings

Oblique roughness replication in strained SiGe/Si multilayers

The replication of the interface roughness in SiGe/Si multilayers grown on miscut Si(001) substrates has been studied by means of x-ray reflectivity reciprocal space mapping. The interface profiles were found to be highly correlated and the direction of the maximal replication was inclined with respect to the growth direction. This oblique replication is explained by the influence of the inhomogeneous strain distribution around step bunches. The formation of step bunches is described by a kinetic step-flow model based on the work by Tersoff et al. [Phys. Rev. Lett. 75, 2730 (1995)]. We have generalized this model by taking into account local variations of the in-plane strain. The angle of obliqueness deduced from these calculations agrees very well with the experimental findings

Spin and energy transfer in nanocrystals without transport of charge

We describe a mechanism of spin transfer between individual quantum dots that does not require tunneling. Incident circularly-polarized photons create inter-band excitons with non-zero electron spin in the first quantum dot. When the quantum-dot pair is properly designed, this excitation can be transferred to the neighboring dot via the Coulomb interaction with either {\it conservation} or {\it flipping} of the electron spin. The second dot can radiate circularly-polarized photons at lower energy. Selection rules for spin transfer are determined by the resonant conditions and by the strong spin-orbit interaction in the valence band of nanocrystals. Coulomb-induced energy and spin transfer in pairs and chains of dots can become very efficient under resonant conditions. The electron can preserve its spin orientation even in randomly-oriented nanocrystals.Comment: 13 pages, 3 figure

Crystal growth near moving contact lines on homogeneous and chemically patterned surfaces

We have systematically investigated how solution crystallization in the proximity of moving contact lines can be modulated by the parameters of the coating flow as well as chemical patterning of the substrate surface. We have studied the monoclinic model substance nicotinamide in the solvent isopropanol, which tends to form needle-like crystals in bulk solution. Three crystallization regimes were identified dependent on the coating speed. At high speeds viscous entrainment dominates over solvent evaporation, and an essentially azimuthally isotopic, spherulithic morphology results. for intermediate speeds a branched morphology with preferential alignment parallel to the coating direction is observed. For low speeds, filament-like crystal patterns well aligned with the coating direction were obtained

Dry-spot nucleation in thin liquid films on chemically patterned surfaces

We systematically study the influence of chemical patterning on the instability of thin liquid films induced by chemical heterogeneities on a flat, horizontal, and partially wetting substrate. We consider common geometric shapes like wedges, circles, and stripes and determine the time required for nucleation of a dry-spot as a function of film thickness, contact angle, pattern dimensions, and geometry. Moreover, we characterized the resulting liquid distribution and identified conditions that avoid the formation of residual droplets on the less wettable regions, which is usually undesirable in technological applications