Molecular Modeling and Simulation of Polymers

Molecular modeling originated with theoretical physicists, who used it to confirm their theoretical models. Molecular simulation uses these models to try to represent reality as closely as possible. It thus becomes a laboratory tool in its own right. The introduction of graphical user interfaces, making the use of calculation codes more user-friendly, is not the only factor behind the fabulous growth in recent years. Increasingly powerful computers and increasingly refined models also contribute to this development.

Molecular simulation of polymers is playing an increasingly important role both in the academic sector and in major industrial R&D centers. It tends to reduce the need for trial and error, which is costly both financially and in terms of time.

However, it must be used in conjunction with more traditional laboratory tools, whether experimental techniques or theory. In this sense, it does not seek to provide, on its own, the "miracle" molecule, i.e. the molecule with all the desired properties, nor to unveil all the microscopic mysteries associated with a macroscopic property. Its purpose remains the prediction of physical properties. It must therefore be used as a guide to the synthesis of new compounds, and to reveal the molecular behaviours that generate the macroscopic properties on which experimental measurements can be based. It is therefore subject to the appropriate use of methods and models.

In order to show the ins and outs of molecular simulation of polymers, this article first presents the basic principles. Given the very high number of atoms to be considered, empirical methods such as molecular mechanics and dynamics are the methods of choice. They are based on the use of a force field expressing the interactions between atoms.

Next, molecular simulation of linear polymers is discussed in the general case. Finally, the most common ways of modeling the amorphous phase of polymers and how to analyze molecular simulation results involving polymers, as well as a few examples of applications of this new laboratory technique, round off this presentation. A brief aside will be made by showing how the melting temperature is determined.