THEORY OF SPIN-DIFFUSION IN LIQUID-PHASE POLYMER SYSTEMS

A general theory of spin diffusion in condensed media is constructed b y the method of Zwanzig-Mori projection operators using the superposit ional approximation to decouple the many-particle correlation function s. The spin diffusion coefficient is expressed in the form D-sp = D-tr + D-f, where D-tr is the contribution associated with translational d isplacements of the molecules and Df is the contribution caused by int ermolecular flip-flop processes. The expression for D-tr differs from the well-known Kubo-Green formula for the self-diffusion coefficient D -sd in that the integrand contains an additional factor P-f(t), which is the probability of the molecular spins not participating in intermo lecular flip-flop transitions over the time t. A microscopic expressio n is obtained for Df in the form of a time integral of the intermolecu lar dipole-dipole dynamic correlation functions. For liquid-phase poly mer system with fairly high molecular mass the condition D-sp much gre ater than D-sd is satisfied. (C) 1998 American Institute of Physics. [ S1063-7761(98)01308-0].