Effects of temperature on elastic behavior of short compact polymers

In this paper, we study further to explore the effects of temperature on the elastic behavior of short compact polymers. Average conformations and thermodynamics statistical properties at various temperatures T are calculated here. Different chain lengths N and elongation ratio lambda are also considered simultaneously. From the plots of f and f(U) vs. elongation ratio at low temperature, we can know that compact polymers are more close to the native states. With temperature decreasing deeply, polymer chains have the tendency to form globular structures. The results are concluded from: the ratio of <L-1(2)>/<L-2(2)> increase abruptly with temperature decreasing at low temperature, and both characteristic ratio <R-2>/Nb-2 and average energy per bond (U) decreases abruptly with temperature decreasing at low temperature, here L-1(2), and L-2(2) are the eigenvalues of the radius of gyration tensor S (L-1(2) less than or equal to L-2(2)). We also analyze the relationship between the heat capacity C-V and temperature T for different chain lengths in the process of tensile elongation. The coil-to-globule transition temperature T, can be estimated from the location of the peak on the heat capacity plot as a function of temperature. The plots of (R) as a function of chain length N at different temperatures are also shown, and the correlation <R-2> similar to N-ce is obtained at T > T-c or T < T-c, while at T = T-c, the plots are irregular, here a depends on temperature and elongation ratio simultaneously. Elastic force (f), energy contribution to elastic force (f(U)), and the ratio f(U)/f are also discussed at various temperatures. These investigations may provide some insights into elastic behaviors of compact polymers at different temperatures, especially at low temperature. (C) 2004 Elsevier Ltd. All rights reserved.