Updates

Physics Seminar: Dr Elena Patyukova

Date: Wednesday 21st of October 2020, 13:30.
Location: Online (MS Teams meeting).

‘Phase behavior of correlated copolymers’

by Dr Elena Patyukova, Department of Chemistry, Durham University, Durham, UK.

Abstract:

Poly(vinyl alcohol) (PVA) is a widely used water soluble, biodegradable polymer. In particular, PVA films are used for packaging of liquid detergents.  PVA cannot be synthesized directly by polymerization of ethenol but instead it is obtained by postpolymerization modification of polyvinyl acetate (PVAc).  Important property of PVA/c copolymers is that degree of randomness of its sequence can be varied by changing conditions of modification reaction and in most general case they are “blocky” (correlated) meaning that segments of one type tend to be arranged in blocks. Phase behavior of PVA/PVAc copolymer when mixed with additives is an important industrial problem and is known to depend strongly both on composition and degree of blockiness. 

In this work, we study phase behavior of the melt of correlated random copolymers such as PVA using mean field Flory-Huggins theory. This is achieved in two steps. At first, we derive a distribution function of copolymer chains with respect to composition and blockiness. Then we use the method of moments, which was developed by Sollich and Cates [Sollich, P.; Cates, M. E.; Phys. Rev. Lett. 1998, 80, 1365–1368] for polydisperse systems, to reduce the number of degrees of freedom of the computational problem.  As a result, we obtain Flory-Huggins phase diagrams for correlated random copolymers. The strongest feature of the developed theory is that fractionation of chains with different compositions and blockiness between coexisting phases is taken into account accurately. We explored how location of transition points and composition of coexisting phases depend on copolymer composition, blockiness and degree of polymerisation. We discuss how our results are connected to the previously developed theories of random copolymers.

Phase diagram of copolymer with chain length N=100, composition f=0.3, blockiness t=0.09. On the left distributions of chains in specified points are shown.

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