(83d) Design of Elastomer Composites with Improved Strength, Heat, and Oil Resistance

This talk presents results obtained from molecular dynamics (MD) simulations of blends of HNBR elastomers and fluorinated elastomers. The simulations enable one to determine mixtures that have high cohesive energy density, improved resistance to oil penetration, and improved mechanical properties at both high and low temperatures. In one approach, perfluoroalkyl side chains are randomly grafted onto HNBR chains to avoid phase segregation of the chemically incompatible HNBR and fluoropolymer in the blends. The COMPASS force field was used to perform the MD simulations. In a typical simulation, a series of NVT simulations is performed. In this part of the simulation the temperature of the system is reduced from 800 K down to 300 K at the rate of 100-K/400-ps. Then, the NPT ensemble is used to obtain the correct density of the system at 1 atm and 300 K. Once we equilibrate the system, we can calculate the cohesive energy density and mechanical properties. To calculate the diffusion coefficient of a gas in the polymer, a long NVT simulation is performed and then, to exclude the disturbance introduced by the thermostat, the NVE ensemble is be applied to the system. The mean square displacement change with time of the gas molecular is calculated to obtain the value of the diffusion coefficient by means of the Einstein relationship. The preliminary results are promising and suggest that one can obtain significant improvements in mechanical properties at a relatively modest increase in price. Some preliminary results will be shown for the diffusion of gases, such as hydrogen sulfide, in the above composites.