AA Anton Darhuber

Bio: AA Anton Darhuber is an academic researcher from Eindhoven University of Technology. The author has contributed to research in topics: Reciprocal lattice & Quantum dot. The author has an hindex of 27, co-authored 121 publications receiving 3563 citations. Previous affiliations of AA Anton Darhuber include Johannes Kepler University of Linz & Princeton University.

Principles of microfluidic actuation by modulation of surface stresses

Abstract: Development and optimization of multifunctional devices for fluidic manipulation of films, drops, and bubbles require detailed understanding of interfacial phenomena and microhydrodynamic flows Systems are distinguished by a large surface to volume ratio and flow at small Reynolds, capillary, and Bond numbers are strongly influenced by boundary effects and therefore amenable to control by a variety of surface treatments and surface forces We review the principles underlying common techniques for actuation of droplets and films on homogeneous, chemically patterned, and topologically textured surfaces by modulation of normal or shear stresses

Slip behavior in liquid films on surfaces of patterned wettability: Comparison between continuum and molecular dynamics simulations

Abstract: We investigate the behavior of the slip length in Newtonian liquids subject to planar shear bounded by substrates with mixed boundary conditions. The upper wall, consisting of a homogenous surface of finite or vanishing slip, moves at a constant speed parallel to a lower stationary wall, whose surface is patterned with an array of stripes representing alternating regions of no shear and finite or no slip. Velocity fields and effective slip lengths are computed both from molecular dynamics (MD) simulations and solution of the Stokes equation for flow configurations either parallel or perpendicular to the stripes. Excellent agreement between the hydrodynamic and MD results is obtained when the normalized width of the slip regions, a/sigma>~O(10), where sigma is the (fluid) molecular diameter characterizing the Lennard-Jones interaction. In this regime, the effective slip length increases monotonically with a/sigma to a saturation value. For a/sigma<~O(10) and transverse flow configurations, the nonuniform interaction potential at the lower wall constitutes a rough surface whose molecular scale corrugations strongly reduce the effective slip length below the hydrodynamic results. The translational symmetry for longitudinal flow eliminates the influence of molecular scale roughness; however, the reduced molecular ordering above the wetting regions of finite slip for small values of a/sigma increases the value of the effective slip length far above the hydrodynamic predictions. The strong correlation between the effective slip length and the liquid structure factor representative of the first fluid layer near the patterned wall illustrates the influence of molecular ordering effects on slip in noninertial flows.

Thermocapillary actuation of droplets on chemically patterned surfaces by programmable microheater arrays

Abstract: We have designed a microfluidic device for the actuation of liquid droplets or continuous streams on a solid surface by means of integrated microheater arrays. The microheaters provide control of the surface temperature distribution with high spatial resolution. These temperature gradients locally alter the surface tension along droplets and thin films thus propelling the liquid toward the colder regions. In combination with liquophilic and liquophobic chemical surface patterning, this device can be used as a logistic platform for the parallel and automated routing, mixing and reacting of a multitude of liquid samples, including alkanes, poly(ethylene glycol) and water.

Microfluidic actuation by modulation of surface stresses

Abstract: We demonstrate the active manipulation of nanoliter liquid samples on the surface of a glass or silicon substrate by combining chemical surface patterning with electronically addressable microheater arrays. Hydrophilic lanes designate the possible routes for liquid migration while activation of specific heater elements determine the trajectories. The induced temperature fields spatially modulate the liquid surface tension thereby providing electronic control over the direction, timing, and flow rate of continuous streams or discrete drops. Temperature maps can be programed to move, split, trap, and mix ultrasmall volumes without mechanically moving parts and with low operating voltages of 2–3 V. This method of fluidic actuation allows direct accessibility to liquid samples for handling and diagnostic purposes and provides an attractive platform for palm-sized and battery-powered analysis and synthesis.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Microfluidics: Fluid physics at the nanoliter scale

Abstract: Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Peclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world.

Engineering flows in small devices

Abstract: Microfluidic devices for manipulating fluids are widespread and finding uses in many scientific and industrial contexts. Their design often requires unusual geometries and the interplay of multiple physical effects such as pressure gradients, electrokinetics, and capillarity. These circumstances lead to interesting variants of well-studied fluid dynamical problems and some new fluid responses. We provide an overview of flows in microdevices with focus on electrokinetics, mixing and dispersion, and multiphase flows. We highlight topics important for the description of the fluid dynamics: driving forces, geometry, and the chemical characteristics of surfaces.

High-Resolution Inkjet Printing of All-Polymer Transistor Circuits

Abstract: Direct printing of functional electronic materials may provide a new route to low-cost fabrication of integrated circuits. However, to be useful it must allow continuous manufacturing of all circuit components by successive solution deposition and printing steps in the same environment. We demonstrate direct inkjet printing of complete transistor circuits, including via-hole interconnections based on solution-processed polymer conductors, insulators, and self-organizing semiconductors. We show that the use of substrate surface energy patterning to direct the flow of water-based conducting polymer inkjet droplets enables high-resolution definition of practical channel lengths of 5 micrometers. High mobilities of 0.02 square centimeters per volt second and on-off current switching ratios of 10 5 were achieved.

Self-cleaning surfaces - virtual realities

Abstract: In the 19th century, Oscar Wilde stated “We live, I regret to say, in an age of surfaces”. Today, we do so even more, and we do not regret it: key advances in the understanding and fabrication of surfaces with controlled wetting properties are about to make the dream of a contamination-free (or 'no-clean') surface come true. Two routes to self-cleaning are emerging, which work by the removal of dirt by either film or droplet flow. Although a detailed understanding of the mechanisms underlying the behaviour of liquids on such surfaces is still a basic research topic, the first commercial products in the household-commodity sector and for applications in biotechnology are coming within reach of the marketplace. This progress report describes the current status of understanding of the underlying mechanisms, the concepts for making such surfaces, and some of their first applications.