How ideal are the ideal-like polymers

The previously unknown long range correlations in the conformations of linear polymers in a $\theta$-solvent were found using analytical calculations and molecular dynamics simulations. Long range power law decay of the bond vector correlation function $\langle\cos\phi\rangle\sim s^{-3/2}$ dominate the standard exponential decay $\langle\cos\phi\rangle = e^{-s/l_p}$, where $\phi$ is the angle between the two bonds, $s$ is their separation along the chain and $l_p$ is the persistence length. These long-range correlations lead to significant deviations of polymer size from ideal with mean square end-to-end distance $\langle R^2 \rangle - b^2N \sim \sqrt N$, where $N$ is the number of Kuhn segments of size $b$. This new phenomena is explained by a fine interplay of polymer connectivity and the non-zero range of monomer interactions. Moreover, it is not specific for dilute $\theta$-solutions and exists in semidilute solutions and melts of polymers. Our results show good agreement with the experimental data on Flory characteristic ratio.