Hydrogels from telechelic polymers: forces and structural changes under shear

Martien Cohen Stuart
Wageningen University The Netherlands
Thursday, March 26, 2015
Schiciano B | 4:30pm

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Water-soluble polymers with two insoluble, sticky ends can form branched structures provided the ends associate to at least trimers. When the concentration is high enough, this leads to physical hydrogels, in which the bonds are not permanent, but can break and reform. We discuss two varieties of telechelics.

One is a classical thickener that typically forms micellar structures at low concentration and gels at higher concentrations. The behavior under shear is highly non-linear, leading to a number of surprising effects. We show how the combination of reversible association and imposed force can explain these effects, and to what extent they resemble geological processes. The behavior of this material can be very well modeled by Brownian dynamics simulations, using a time-dependent micelle-micelle interaction potential; a whole 'dynamics phase diagram' of disspative structures emerges.

The other is a sequence-controlled polypeptide obtained biosynthetically by recombinant techniques. A special feature of this polymer is its capability to form exactly trimeric nodes, the minimum required for network formation. Since the polymers is strictly monodisperse, too, it is possibly to construct, on the basis of independent thermodynamic and kinetic data, a truly predictive model for the modulus as a function of  temperature and concentration, which agrees very well with the data. We finally discuss the behavior under large deformations and self-healing properties.