SINGLE-CHAIN STRUCTURE IN MODEL POLYETHYLENE MELTS

The rotational isomeric state (RIS) model is usually considered to be an excellent description of the single-chain structure of polymer chains both in the melt and in THETA-solvents. The manifestation of this single-chain structure (commonly measured by scattering experiments) is the correlation function omega(r), which is the probability that two sites on the same chain are separated by a distance r. The evaluation of omega(r) from the RIS model requires laborious statistical averages, and, as a consequence, various approximations of omega(r) are of importance. Previous approximation schemes have focused on the long-wavelength regime. However, many physical phenomena and properties are very sensitive to local correlations and understanding such behavior requires an approximate omega(r) which is accurate on all length scales. We present such an approximation here and compare it to both computer simulation and previous, more coarse-grained approaches.