SKM 2023 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 54: Complex Fluids and Colloids, Micelles and Vesicles (joint session CPP/DY)

DY 54.11: Vortrag

Freitag, 31. März 2023, 12:30–12:45, MER 02

Diffusion and thermodiffusion of polymers in mixed solvents — •Daniel Sommermann, Jannik Kantelhardt, and Werner Köhler — Physikalisches Institut, Universität Bayreuth, Germany

We present experiments on diffusion and thermodiffusion of polymers in mixed solvents. So far, most works on thermodiffusion have dealt with binary systems or ternary mixtures of small molecules. Binary samples with polymers in solvents have been studied over both a broad concentration and polymer molar mass range. Only a few very recent experiments measured polymers in a binary solvent. In this work, samples made of polystyrene (M_w = 4880 g/mol), toluene and cyclohexane have been analysed using multi-color optical beam deflection (OBD) and supporting single-color thermal diffusion forced Rayleigh scattering (TDFRS). While binary mixtures are readily characterized by one diffusion and one thermodiffusion coefficient, the number of coefficients increases to four plus two for ternaries. The measured signals show three well separated modes that can be assigned to the thermal diffusivity and the two eigenvalues of the mass diffusion matrix. We are particularly interested in the question, to what extent the dynamics of the large entity, the polymer, is coupled to the solvent-solvent dynamics, both with respect to diffusion and thermodiffusion. A first analysis supports the picture of an effective solvent whose internal dynamics is decoupled from the one of the polymer.