Multiscale Modelling of Polymers at Interfaces

Abstract

The structure and dynamics of polymers at liquid and solid interfaces has been a popular topic in statistical physics for a long time now. The molecular-level understanding of these systems is crucial in a variety of technological applications ranging from the development of drug delivery nano-carriers, the optimisation of separation processes to the synthesis of polymer composites and protective coatings. A detailed insight into the equilibrium properties of these many-body systems can be achieved within the framework of statistical mechanics and particle-based simulations provide an efficient tool for this purpose. Due to the inherent mesoscale behaviour of polymeric systems, the use of reduced order coarse-grained models, that do not consider every single atom, is an effective choice for efficiently studying system properties on large length and time scales. The first part of this thesis is devoted to studying the behaviour of polymers entrapped at the interface of two immiscible fluids, using coarse-grained models. Dynamics and structure analyses demonstrate that when the viscosity of the two liquid phases is different enough, the polymer dynamics changes to a regime where the hydrodynamics interactions are screened. To obtain a detailed insight into the thermodynamic properties of polymer-filler systems, atomistic simulations are employed. To evaluate the solid-liquid interfacial tensions and the corresponding work of adhesion, which determines the magnitude of polymer-filler adhesion, local stress fields analyses are performed. A reduction of the work of adhesion with increasing temperature is observed, while it is almost independent of the polymer molecular weight. The work presented in this thesis is also focused on the development of simple coarse-grained models of polymer composites, mainly employed in automotive applications. Using these models, polyisoprene melts and plasticisers (low molecular weight diluents added in the compound to improve its workability) in contact with carbon-black fillers are investigated. A detailed structural analysis of such systems reveals that the presence of the solid substrate strongly affects the conformation of the polymer chains, which present a highly packed and highly entangled local network. This local conformation, in turn has profound effects on the mechanical and rheological properties of the final composites. A systematic analysis on the effect of plasticisers shows that their functionality is greatly affected by their conformational flexibility and their affinity with the filler. Therefore, the choice of such molecules during the synthesis of polymer composites is not trivial and this work provides simple geometrical design rules to optimise the structure of plasticisers to meet specific requirements of the final composite.

Date of Award	31 Aug 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Paola Carbone (Supervisor) & Matthieu Gresil (Supervisor)