Analytical results of the extensible freely jointed chain model

Abstract

Based on classical statistical mechanics, we calculate analytically the length extension and the fluctuations, under a pulling force, of a polymer modelled as a freely jointed chain with extensible bonds, the latter considered as harmonic springs. We obtain an analytical formula for the partition function, and derive both the extension curve of the chain and the fluctuations as a function of the force. An independent high force approximation has been also evaluated. The analytical formulas have been validated by analysing the exactness of their fit on data obtained from Langevin simulations, and compared with the phenomenological expressions largely used in the past literature.