Computer simulations of polymeric functional materials

Molecular Dynamics (MD) is a widely used methodology for investigating the dynamic behavior of soft matter at a level of detail that is hardly accessible by experiments. Fundamentals of MD simulations start by covering Newton's equations, the basis of classical mechanics, and then continue to Force-Field (FF) methods for modeling potential energy surfaces. MD simulations are commonly carried out at the all-atom level: thanks to tremendous advances in computer techniques and algorithms, millisecond-scale simulations are now feasible for smaller systems and proteins. Yet, since this span may not be enough to cover the time scale of biological events, many research efforts have been devoted to reducing, or in other words, coarse-graining, the atomistic representation in order to extend the time and length scale of simulations. In this thesis, both the all-atom and coarse-grain methodologies were exploited to investigate two polymeric systems. After introducing the theoretical background of the simulation technique (Chapter 1), Chapter 2 illustrates the application of all-atom MD simulations to the determination of the elastic properties of two well-known semiconducting polymers, i.e. PBTTT and IDTBT, in their amorphous and crystalline phases. The prediction of mechanical properties, namely the Young moduli and the Poisson's ratios, was fulfilled by the calculation of the stiffness tensor using linear elasticity equations. The last part of the thesis (Chapter 3) reports the study of the self-assembly in solution of the oligomeric sequence GCCG, by performing MD simulations using the coarse-grained oxDNA model. The focus was set on the deduction of the mechanism employed for the self-assembly process and on the verification of a liquid crystalline (LC) ordering that this sequence is predicted to show. We empowered our computational findings with the good agreement that was found with experimental results.