Speaker
Mr
Nico König
(Jülich Centre for Neutron Science JCNS and Institute for Complex Systems ICS, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany AND Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, Oslo, Norway)
Description
Here we present a kinetic study on the chain exchange in mixed polymeric micelles containing partially crystalline cores. We are specifically interested in understanding how cooperative phenomena such as crystallization and melting affect the dynamics of self-assembled systems. As a model system we use n-alkyl-PEO ($C_{n}H_{2n+1}-O-(CH_{2}-CH_{2}-O)_{100}H$) with a molecular weight of roughly 5 kg/mol. In water these molecules form star-like micelles with a strongly segregated alkane core that partially crystallizes. This creates an additional energy barrier that needs to be overcome during chain expulsion.[1] We employ time-resolved small-angle neutron scattering in combination with the kinetic zero-average contrast technique to track the exchange kinetics.[2]
We investigated mixtures of C28-PEO and C22-PEO and determined the respective melting enthalpies using differential scanning calorimetry (DSC) which was quantitatively compared to the kinetic data obtained from TR-SANS. We found that the core crystallization occurs cooperatively while the intermicellar chain exchange processes of C28-PEO and C22-PEO are virtually decoupled. Nevertheless the cooperative crystallization affects the separate exchange kinetics of both species.
[1] Zinn, T., Willner, L., Pipich, V., Richter, D. and Lund, R. Effect of Core Crystallization and Conformational Entropy on the Molecular Exchange Kinetics of Polymeric Micelles. ACS Macro Letters 4, 651-655, doi:10.1021/acsmacrolett.5b00197 (2015).
[2] Willner, L., Poppe, A., Allgaier, J., Monkenbusch, M. and Richter, D. Time-resolved SANS for the determination of unimer exchange kinetics in block copolymer micelles. Europhys. Lett. 55, 667-673, doi:DOI 10.1209/epl/i2001-00467-y (2001).
Primary author
Mr
Nico König
(Jülich Centre for Neutron Science JCNS and Institute for Complex Systems ICS, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany AND Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, Oslo, Norway)
Co-authors
Dr
Lutz Willner
(Jülich Centre for Neutron Science JCNS and Institute for Complex Systems ICS, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany)
Prof.
Reidar Lund
(Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, Oslo, Norway)
Dr
Thomas Zinn
(ESRF – The European Synchrotron, 38043 Grenoble, France)
Dr
Vitaliy Pipich
(Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH, Outstation at MLZ, Lichtenbergstrasse 1 85747 Garching, Germany)
