Berlin 2015 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 21: Polymer dynamics

CPP 21.11: Vortrag

Dienstag, 17. März 2015, 12:15–12:30, C 264

Thermophoresis of linear polymers: is it Rouse or Zimm? — •Werner Köhler¹ and Konstantin Morozov² — ¹Physikalisches Institut, Universität Bayreuth, D-95440 Bayreuth, Germany — ²Department of Chemical Engineering, Technion Israel Institute of Technology, Haifa 32000, Israel

Polymer thermophoresis, the migration of dissolved polymer chains along a temperature gradient, is independent of molar mass for sufficiently long chains. Systematic experiments in our group have shown that the relevant units are not the monomers but rather correlated entities of the size of the Kuhn segment. The molar mass independent thermophoretic mobility has been interpreted in the literature in terms of a Rouse-type dynamics based on a draining coil model. Recent results reported for linear chains, crosslinked microgels, and core-shell particles of the thermoresponsive polymer PNIPAM together with older data for copolymers suggest, however, a non-draining coil with hydrodynamic coupling (Zimm). We show that the relevant thermophoretic interactions decay ∝ r⁻² and, thus, much slower than the short-ranged (∝ r⁻⁶) van der Waals interactions. In consequence, thermophoresis results from volume rather than surface forces. The hydrodynamic flow penetrates only into a boundary layer of the coil and causes tangential stress on the coil as a whole, and not on the scale of the individual segments. The experimentally observed molar mass independence of the thermophoretic mobility naturally follows from the model.