Showing papers by "Friedrich Gunther Mugele published in 2007"
TL;DR: In this paper, a combined numerical, analytical, and experimental approach was used to determine the equilibrium surface profile for electrowetting, and it was shown that the local surface curvature diverges algebraically upon approaching the contact line with an exponent −1 <μ<0.
Abstract: Electrowetting is becoming a more and more frequently used tool to manipulate liquids in various microfluidic applications. On the scale of the entire drop, the effect of electrowetting is to reduce the apparent contact angle of partially wetting conductive liquids upon application of an external voltage. Microscopically, however, strong electric fields in the vicinity of the three phase contact line give rise to local deformations of the drop surface. We determined the equilibrium surface profile using a combined numerical, analytical, and experimental approach. We find that the local contact angle in electrowetting is equal to Young's angle independent of the applied voltage. Only on the scale of the thickness of the insulator and beyond does the surface slope assume a value consistent with the voltage-dependent apparent contact angle. This behaviour is verified experimentally by determining equilibrium surface profiles for insulators of various thicknesses between 10 and 250 µm. Numerically and analytically, we find that the local surface curvature diverges algebraically upon approaching the contact line with an exponent −1<μ<0. We discuss the relevance of the local surface properties for dynamic aspects of the contact line motion.
137 citations
TL;DR: In this paper, the swelling behavior of copolymer microgel particles made of poly(N-isopropylacrylamide)-co-vinylacetic acid using dynamic light scattering (DLS), neutron scattering, and in situ atomic force microscopy (AFM) was studied.
119 citations
TL;DR: A one-dimensional harmonic oscillator model is developed that describes the dependence of the drop oscillations on the relevant intrinsic (surface tension, viscosity, density) and extrinsic (wire height, voltage) parameters.
Abstract: We studied millimeter-sized aqueous sessile drops in an ambient oil environment in a classical electrowetting configuration with a wire-shaped electrode placed at a variable height above the substrate. Within a certain range of height and above a certain threshold voltage, the drop oscillates periodically between two morphologies where it is either attached to the wire or detached from it. We determine the range of control parameters, wire height, and voltage in which oscillations occur and explain it by a simple capillary model. Furthermore, we analyze the dynamics of the oscillations using high-speed video microscopy and numerical fluid dynamics modeling. We develop a one-dimensional harmonic oscillator model that describes the dependence of the drop oscillations on the relevant intrinsic (surface tension, viscosity, density) and extrinsic (wire height, voltage) parameters.
35 citations