THE CORRELATION-FUNCTIONS OF HARD-SPHERE CHAINS - MONODISPERSE CHAINSAS A COMPLETE ASSOCIATION LIMIT

The mixture of associating hard spheres with two random association si tes is considered to model freely jointed tangent hard-sphere chains o f fixed length. In the case of the complete association limit with inf inite association strength, the associating fluid becomes the hard-sph ere chain fluid. The multidensity Ornstein-Zernike equation is applied to this limiting case, and an analytical solution is obtained within the polymer Percus-Yevick (PPY) approximation. In doing so, we imposed connectivity constraints between bonded segments in order to avoid nu merically inconvenient forms. Explicit expressions for the contact val ues of the correlation functions are obtained, and the correlation fun ctions for the region beyond the hard core are calculated from a set o f integral equations involving only finite quantities. Predictions of the theory for 4- and 8-mer fluid are compared to computer simulation results. For overall correlation functions accurate predictions are ob tained over the whole density range. For the inter- and intramolecular correlation functions, a significant improvement is found at low dens ity compared to our previous theory with the PPY ideal-chain approxima tion. As chain length increases, the theory overestimates the intermol ecular correlation functions, and underestimates the intramolecular co rrelation functions. It is concluded that the good accuracy for the ov erall correlation functions is due to the cancellation of errors betwe en the inter- and intramolecular correlation functions. (C) 1998 Ameri can Institute of Physics.