Berlin 2015 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 46: P11: Wetting, Micro and Nano Fluidics

CPP 46.14: Poster

Wednesday, March 18, 2015, 10:00–13:00, Poster A

Thermocapillary Convection in Microfluidic Devices — •Lorenz Butzhammer and Werner Köhler — Physikalisches Institut, Universität Bayreuth, 95440 Bayreuth, Germany

Thermocapillary convection has been investigated experimentally at a liquid-air interface in a PDMS-based microfluidic device. Fluid dynamics in the vicinity of the meniscus, which is located at a T-junction of the 100-µ m-wide channels, is observed using an inverted light microscope. A temperature gradient along the interface is set up through a focused laser beam (532 nm) and an absorbing dye at a low concentration. This leads to tangential Marangoni stresses and liquid flow towards regions with lower surface tension. Samples included water, ethanol, glycerol and binary mixtures of those with polystyrene beads (d=100-600  nm) for flow visualization. Data evaluation was done using Particle Image Velocimetry (PIV) and Ghost Particle Velocimetry (GPV). Experiments show that the effect is absent in water and water-glycerol mixtures within the investigated temperature range. However, in ethanol, asymmetric convection rolls perpendicular to gravity already arise without an external heat source. The flow strength and direction can be manipulated by laser heating, leading to fluid motion towards lower temperatures. In symmetric mixtures containing ethanol the direction is reversed. Moreover, the onset and strength of the self-induced convection rolls at these concentrations strongly depend on repositioning of the meniscus.