Martin Lisal, Institut for Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, Rozvojova 135, Prague, CZ-165 02, Czech Republic, John K. Brennan, Weapons and Materials Research Directorate, U.S. Army Research Laboratory, Building 4600, Aberdeen Proving Ground, MD 21005, and William R. Smith, Faculty of Science, University of Ontario Institute of Technology, 2000 Simcoe St. N., Oshawa, ON L1H7K4, Canada.
We present a mesoscale simulation technique, termed the Reaction Ensemble Dissipative Particle Dynamics method (RxDPD), for studying reaction equilibria of polymer systems. The RxDPD method combines elements of dissipative particle dynamics (DPD) [Hoogerbrugge and Koelman 1992; Koelman and Hoogerbrugge 1993] and reaction ensemble Monte Carlo (RxMC) [Smith and Tríska 1994; Johnson
et al 1994], allowing for the determination of both static and dynamical properties of polymer systems. The reaction equilibrium of the polymer system evolves deterministically in time according to the DPD equations of motion. The time evolution of the system is accompanied by changes in a coupling parameter associated with a fractional particle that mimics the forward and reverse reaction steps of the RxMC method. RxDPD can be used to predict the polydispersity due to various effects, including solvents, additives, temperature, pressure, shear and confinement. The ability to predict polydispersity is a critical step towards a more complete model description of the actual system. The polydispersity of the system is not specified a priori but rather determined from the RxDPD simulation. Analogous to polymerization processes performed in the laboratory, the resulting polydispersity is affected by processing conditions such as the pressure and temperature, and by the material properties which in the RxDPD method are specified via the polymer ideal-gas properties. To demonstrate the method, we have simulated the thermodynamic, structural and dynamical properties of several simple polydispersed polymer systems, including the equation of state, radial distribution function, end-to-end distance, radius of gyration, and self-diffusion coefficient. Extensions of the method to other polymer systems such as grafted polymers, cross-linked polymers, block copolymers, and reactive polymer blends are straightforward.
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