The Magnitude of the Soret Force on Colloidal Particles Measured in Microgravity

There is a broad interest in both industry and academe in understanding the time-evolution in the microstructure of colloidal gels, as such changes affect the properties of the gels including product self-life and rheology. In colloidal gels, the time-evolution results from the magnitude and the relative proportions of forces—including gravity, acting on the colloidal particles. The aim of this study was to measure the magnitude of the Soret force acting on the colloidal particles in a model gel in the microgravity on the International Space Station, as a proxy for gravitational forces in Earth-based experiments. It was found that the Soret force could be used to create an effective gravitational force of between about 10 × 10−17 N (3 milli-G) and 3 × 10−17 N (1 milli-G) on the colloidal particles, where the lower limit is set by the dominance of particle flux from Brownian forces. These results should allow mapping the behavior of colloidal gels broadly described in literature on other gels—such as polymer gels of industrial interest, where the colloidal particles are much smaller.