Dresden 2020 – wissenschaftliches Programm
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CPP 59.10: Vortrag
Mittwoch, 18. März 2020, 12:00–12:15, ZEU 114
Polymer Micelles with Crystalline Cores: self-assembly, molecular exchange kinetics and confinement effects — Nico König1, Lutz Willner2, and •Reidar Lund1 — 1Department of Chemistry, University of Oslo, Norway — 2Institute for Complex Systems ICS, Forschungszentrum Jülich, Germany
Partially crystalline, self-assembling systems with multiple components are omnipresent in nature with living cells as a prominent example. Here we study micelles formed by self-assembly of a series of well-defined n-alkyl-(polyethylene oxide) (Cn-PEO) polymers in aqueous solutions . By using small-angle X-ray scattering (SAXS), densiometry and differential scanning calorimetry (DSC), we show that the n-alkane exhibit a first-order phase transition, but with reduced melting points compared to bulk. Correlating the structural and thermodynamic data, we found that the melting depression can be accurately described by the Gibbs-Thomson equation. The effect of core crystallinity on the molecular exchange kinetics is investigated using time-resolved small-angle neutron scattering (TR-SANS). We show that the melting transition is cooperative in the confined micellar core, whereas the exchange process is widely decoupled and unimeric in nature. Upon crossing the melting point, a discrete change in the activation energy is found. This suggests that a "local, single-chain melting process" preludes the molecular diffusion out of the micelle during chain exchange