SKM 2023 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 8: Responsive and Adaptive Systems
CPP 8.1: Talk
Monday, March 27, 2023, 10:45–11:00, ZEU 255
Spreading drops of volatile oil induce long range thickness gradients in swelling hydrophobic polymer brush layers — •Özlem Kap1, Simon Hartmann2, Harmen Hoek1, Igor Siretanu1, Sissi de Beer3, Uwe Thiele2, and Frider Mugele1 — 1University of Twente, Physics of Complex Fluids, PO Box 217, 7500 AE Enschede (NL) — 2Westfälische-Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 9, 48149 Münster (D) — 3University of Twente, Sustainable Polymer Chem., PO Box 217, 7500 AE Enschede (NL)
Polymer brush layers are responsive materials that swell in contact with good solvents and their vapors. We combined optical experiments and numerical calculations based on gradient dynamics of a free energy density to study how fluid flow and solvent diffusion control the macroscopic spreading of (weakly) volatile oil drops and the swelling kinetics of an underlying hydrophobic polymer brush layer. The macroscopic spreading dynamics follow algebraic law with an exponent of 1/6, yet the spreading drops are found to be surrounded by halos of partially swollen polymer brushes. The width of the halos reaches values of hundreds of micrometers wide within hours to days, with thickness variations ranging from the dry thickness up to a maximum swelling ratio of ~4 close to the contact line. The halo profiles display long-living non-equilibrium steady state configurations that are controlled by the competition of two transport mechanisms, solvent diffusion through the polymer brush layer and through the vapor phase.