Topological interactions: Understanding viscoelasticity on the nano-scale

Polymers exhibit complex flow properties. One example is the pronounced non Newtonian behavior or in other words the change in viscosity with shear rate.

The distinctive changes in the shear and loss moduli can be explained on microscopic scales and be connected to internal relaxation processes of the molecules. The reptation model assumes two prominent relaxation processes defining the characteristics of polymers. One, the Rouse time, is related to the local relaxation of chain segments.

The second one, the tube relaxation time, results form the topological confinement imposed on the chain dynamics and resulting from entanglements of polymer chains, enforcing a repative motion along a tube.

This theory is exceptionally successful in predicting correct scaling laws but fails to describe exerimental observations made under shear/deformation.At rest the reptation model has been verified by neutron scattering techniques, combining a high sensitivity to light elements with the right time and length scales to probe local structures and dynamics.

However, experiments done at shear rates exceeding the linear regime are very scarce. Such exepriments allow to test recent theories and simulations going beyond the original reptation model. Recently, we have created the capabilities to do such experiments and done first test measurements. In this project we will experimentally connect viscielasticity to topological interactions in polymers under shear.