Diffraction by macromolecular fluids

X-Ray diffraction data on n-alkane fluids ranging from n-butane to polyethylene are analysed to yield the relative contributions from intra- and inter-molecular scattering. The intramolecular contributions are calculated from an exact rotational-isomeric-state model at short length scales, and approximated by a semiflexible chain model on global scales. With increasing chain length, the intermolecular pair distribution functions show a general decrease in short-range structure along with the predicted self-screening, or de Gennes 'correlation hole', whereby sites on different chains are partially excluded from close approach to sites on a given chain.