Elena Akhmatskaya1 and José M. Asua2
1 Basque Center for Applied Mathematics (BCAM), Alameda de Mazarredo 14
48009 Bilbao, Spain
2 POLYMAT and Grupo de Ingeniería Química, Departamento de Química Aplicada, Facultad de Ciencias Químicas; University of the Basque Country UPV/EHU, Joxe Mari Korta zentroa, Tolosa etorbidea 72, Donostia-San Sebastián 20018, Spain

This movie presents the evolution of the morphology of a particle formed by polymerization of a miniemulsion droplet initially containing a monomer (cyan) and a preformed polymer (red) with formation of graft copolymer. The movie also represents a seeded emulsion polymerization in which the seed is swollen with monomer. The aqueous medium is represented by white spheres.
A 200 nm particle with an initial composition polymer/monomer=50/50 wt/wt is simulated as a group of spheres. Each polymer sphere represents a polymer chain of a molecular weight of about 750000 g/mol. In addition, the monomer spheres contain the number of molecules needed to form a polymer chain.
During polymerization, a fraction of the monomer (80% in this simulation) is converted into polymer (blue) and the rest is grafted on the preformed polymer. The graft copolymer is represented in green.
A stochastic dynamics simulation was carried out using the velocity Langevin dynamics performed in the NVT ensemble (constant number of spheres and total volume and well-defined temperature). Lennard-Jones potentials were used to model the interaction between similar phases (e.g., monomer and polymer) and a repulsive generalized soft sphere potential was used for the interactions between dissimilar phases (e.g., polymer-water).
The movie shows that polymerization and morphology evolution occurred simultaneously and that the different phases migrate because of the interplay between interactions and Brownian motion. The simulation was allowed to reach equilibrium in which the graft copolymer was placed between the two polymers to minimize the overall energy of the system.