Temperature dependence of thermodiffusion in aqueous suspensions of charged nanoparticles

Measurements of particle flows driven by temperature gradients are conducted as a function of temperature on aqueous suspensions of polystyrene nanoparticles and proteins of T4 lysozyme and mutant variants of T4 lysozyme. The thermodiffusion coefficients are measured using a microfluidic beam deflection technique on suspensions with particle concentrations on the order of 1 vol %. At T ≲ 20 °C, all of the nanoparticles studied migrate to the hot regions of the fluid; i.e., the thermodiffusion coefficient is negative. At higher temperature, T ≳, 50 °C, the thermodiffusion coefficient is positive with a value consistent with the predictions of a theoretical model originally proposed by Derjaguin that is based on the enthalpy changes due to polarization of water molecules in the double layer.