Elastic behavior of non-Gaussian polymethylene chains

In this paper, elastic behaviors of non-Gaussian polymethylene (PM) chains with chain length N = 100 are investigated by rotational isomeric state model. Here the tetrahedral lattice of PM chain and the non-local interaction of Sutherland potential are adopted. In the metropolis movement of PM chain, a four-bond movement model is used. The average energy and average Helmholtz free energy with various elongation ratios lambda, are calculated by Monte Carlo simulation method. The average energy increases with elongation ratio lambda, and the average Helmholtz free energy decreases with elongation ratio lambda. The elastic force f and the energy contribution to elastic force f(u) can be obtained from f = partial derivative<A>/partial derivativer and f = partial derivative<U>/partial derivativer. We find that the elastic force f increases with elongation ratio lambda and the energy contribution f(u) decreases with elongation ratio lambda, and f(u) is less than zero. The ratio f(u)/f is close to -0.21 for lambda less than or equal to 1.25, and -0.04 to -0.35 for lambda > 1.25 at T = 364 K. In our calculation, the rubber elasticity may be discussed in terms of the chemical structure of polymer chains. (C) 2002 Elsevier Science Ltd. All rights reserved.