(709g) Molecular Calculations towards Simulating Effects of Elastomer/Filler Interactions On Rolling Resistance in Rubber Tires

Viscoelastic losses lead to rolling resistance and energy dissipation in rubber tires. When a tire tread flattens, elastomer conformations change.  Deformations at high frequencies result in energy losses that contribute to traction, while entropy changes at low frequency contribute to rolling resistance. A balance needs to be maintained between reducing rolling resistance and improving or maintaining traction. A molecular modeling approach is being developed to help simulate how elastomer/filler interactions in low rolling resistance tread compounds can lead to an improvement in fuel economy. Computations are inspired from the Rotational Isomeric State (RIS) approach of Flory in which the distribution of conformation energies are considered over discrete isomeric states. Intramolecular energies of chain segments within styrene butadiene rubber (SBR) were calculated as a function of conformation; intermolecular energies of interaction between SBR chains and filler particles were also calculated. Rotational isomeric state probabilities were computed, which enabled sequences of torsion angle rotational isomeric state to be obtained and thus shapes of an elastomer chain to be generated. The probability distribution of squared end-to-end distance of a chain was computed. Changes in distribution of chain sizes due to filler interactions indicate filler effects on conformation. The results from RIS computations are to be used in calculating molecular-level changes in storage and loss modulus as a function of frequency.