Mesoscopic Simulation of Polymers

Polymers are a class of materials of great interest to the chemical and materials industries. In fact, they are among the chemical industry's highest-volume products and most profitable materials. Few new industrial polymers are being developed, however, and they remain mainly the preserve of academic research. The cost of bringing them to market is a limiting factor. What industry is looking for instead is to obtain specific properties by blending polymers, or synthesizing copolymers. Just think of ABS, the terpolymer used in the manufacture of the first tires. This copolymer combines rigidity, hardness and heat resistance, thanks to the right combination of three monomers. Nevertheless, a strong experimental component is required to find the best compromise, i.e. the composition of the different polymers or links in the copolymer, offering the optimum property (while preserving the other properties). In order to overcome the time and cost problems associated with the search for the best candidate, molecular simulation is proving to be ideally suited.

The choice of the most appropriate simulation method for an industrial application depends mainly on the level of detail required. When studying mixtures, demixing occurs because the entropy of mixing is much lower when one of the constituents is a polymer, compared with mixtures of low-molecular-weight molecules. The material will therefore present domains rich in one or other of the compounds. By modulating the interface tension between the two components, the morphology of the material is altered, enabling the desired properties to be obtained. Knowledge of the morphology of the polymeric system is therefore essential for fine-tuning properties of importance to practical applications. The level of detail associated with morphology corresponds to the so-called mesoscopic scale. The approach discussed in this article goes from the microscopic to the macroscopic: in English, the terms "bottom-up" are used. The opposite, "top-down", will not be discussed.