Elastic behavior of adsorbed polymer chains.

Elastic behaviors of single polymer chains adsorbed on the attractive surface are first investigated using Monte Carlo simulation method based on the bond fluctuation model. We investigate the chain size and shape of adsorbed chains, such as mean-square radius of gyration 〈S²〉, mean-square bond length 〈b²〉, shape factors 〈sf_i〉 and 〈δ*〉, and the orientation of chain segments P₂〈cos θ〉, to illuminate how the shape of polymer chains changes during the process of tensile elongation. There are some special behaviors of the chain size and shape at the beginning of elongation, especially for strong attraction interaction. For example, mean fraction of adsorbed segments decreases abruptly in the region of small elongation ratio and then decreases slowly with increasing elongation ratio. In fact, the chain size and shape also changes abruptly for small elongation ratio with strong attraction interaction. Some thermodynamics properties are also investigated here. Average Helmholtz free energy increases fast for elongation ratio λ<1.15, especially with strong attraction, and increases slowly for λ>1.15. Similar behaviors are obtained for average energy per bond. Elastic force (f ) and energy contribution to force (f_U) are also studied, and we find that elastic force decreases abruptly for λ<1.15, and there is a minimum of elastic force for strong attraction interaction, then increases very slowly with increasing elongation ratio. However, there are different behaviors for weak attraction interaction. For energy contribution to force (f_U), there is a maximum value for strong attraction interaction in the region of λ<1.15. Some comparisons with the atomic force microscopy experiments are also made. These investigations may provide some insights into the elastic behaviors of adsorbed polymer chains. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]