Analysis of the mass transport properties of the binary polymeric mixture in microgravity conditions during the DCMIX4 campaign onboard the ISS. Comparison with gravity-based experiments

We present the results of thermodiffusion experiments conducted under microgravity conditions during the DCMIX4 mission performed onboard the International Space Station (ISS). The space data are compared to previously obtained ground-based measurements. The investigated binary mixture, composed of polystyrene (4730 g/mol) dissolved in the pure solvent toluene, was analysed at four different operating temperatures: 20-25-30-35 °C. A complete procedure was developed, detailing each step from data acquisition to the determination of the fluid transport properties (Soret, molecular diffusion, and thermodiffusion coefficients) using various analytical solutions. Experimental results for the Soret coefficient (steady-state species separation analysis) indicate a linear decrease with increasing temperature, which is in excellent agreement with the Soret coefficients obtained under ground-based thermodiffusion experiments. In contrast, the molecular diffusion coefficient (unsteady-state study) exhibits an increasing trend with temperature, presenting larger deviations from gravity-based results. These variations are attributed to inaccuracies in phase reconstruction because of limitations in the employed phase-stepping technique.