Micron-scale apparatus for measurements of thermodiffusion in liquids

An ac beam deflection technique for measurements of thermodiffusion in liquid mixtures is described. In comparison to conventional beam deflection methods, the micron-scale geometry of our apparatus speeds up equilibration by a factor of approximate to300. Our apparatus and analysis methods are validated with measurements on molecular polystyrene dissolved in toluene. Thermodiffusion experiments on 26 nm polystyrene colloids with carboxyl functionality (COOH) in water yield Soret coefficients of S-T= -0.28+/-0.025 K-1. (C) 2004 American Institute of Physics.