Telechelic polymers, bearing two hydrophobic stickers in terminal position with a water soluble backbone, are well-studied model systems for self-assembly. Their properties encompass many interesting aspects of soft matter physics – including hierarchical self-assembly, non-Newtonian flow behaviour, and colloidal interactions. Furthermore, telechelic polymers are very important as associative thickeners in products used in daily life, e.g. paints and cosmetics.
In this work, we have investigated the molecular exchange kinetics in mixtures of mono- and difunctionalized telechelic poly(ethylene oxide) n-alkylethers using time-resolved small angle neutron scattering. The results show that, contrary to regular micelles consisting of only monofunctional molecules, the kinetics proceed in a multistep process involving a collision-induced single-molecule exchange mechanism where the rate is directly proportional to the polymer concentration. Based on experimental findings, we have derived a simple kinetic model summarized in the figure below. It consists of three consecutive steps:
- expulsion of one telechelic chain end,
- insertion into another micelle, i.e. bridging, and
- release of the second chain end.
A single exponential decay of the relaxation function with an effective rate constant, , that linearly depends on the micellar concentration is in excellent accord with the experimental findings. The discovered collision-induced exchange mechanism is relevant also to other self-assembled structures, in which multivalency plays a role, e.g. in supramolecular networks, lipid membranes, multidomain proteins, lipoproteins, and conventional hydrogels.
Forschungszentrum Jülich – Neutron Scattering and Soft Matter (JCNS-1)