Theory of spin diffusion in liquid-phase polymer systems
Theory of spin diffusion in liquid-phase polymer systems
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液相聚合物体系中的自旋扩散理论
DOI：
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
E. Fischer
中科院分区：
文献类型：
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作者：
N. Fatkullin;G. Yatsenko;R. Kimmich;E. Fischer
利用Zwanzig-Mori投影算符方法，利用叠加近似解耦多粒子关联函数，建立了凝聚介质中自旋扩散的一般理论。自旋扩散系数表示为dsp=dtr+df，其中dtr是与分子的平移位移有关的贡献，df是分子间触发过程引起的贡献。Dtr的表达式不同于著名的自扩散系数DSD的Kubo-Green公式，因为被积函数包含一个附加因子Pf(T)，它是分子自旋在时间t内不参与分子间触发器跃迁的概率。得到了分子间偶极-偶极动态关联函数时间积分形式的Df的微观表达式。对于相对分子质量较高的液相聚合物体系，满足DSPDSD条件≫。
A general theory of spin diffusion in condensed media is constructed by the method of Zwanzig-Mori projection operators using the superpositional approximation to decouple the many-particle correlation functions. The spin diffusion coefficient is expressed in the form Dsp=Dtr+Df, where Dtr is the contribution associated with translational displacements of the molecules and Df is the contribution caused by intermolecular flip-flop processes. The expression for Dtr differs from the well-known Kubo-Green formula for the self-diffusion coefficient Dsd in that the integrand contains an additional factor Pf(t), which is the probability of the molecular spins not participating in intermolecular flip-flop transitions over the time t. A microscopic expression is obtained for Df in the form of a time integral of the intermolecular dipole-dipole dynamic correlation functions. For liquid-phase polymer system with fairly high molecular mass the condition Dsp≫Dsd is satisfied.