Self-diffusion and nuclear magnetic relaxation in liquid methane-argon mixtures

The spin echo method was used to measure the self-diffusion coefficients of CH4 and the spin–lattice relaxation times T1 in liquid CH4−Ar mixtures over the entire range of concentrations and at temperatures 100 ≤ T ≤ 150°K along the liquid-vapor curve. The experimental relations D(x, T) are shown to be in qualitative agreement with conclusions based on the assumption of individual (“single-particle”) and collective hydrodynamic contributions to the diffusion processes. The maxima on the T1(T) curves were found to shift to lower temperatures with an increase in concentration, this being attributed to an increase in the spin-rotational contribution to the relaxation rate. Separating this contribution, we determined the x, T dependences of the orientational and angular-velocity correlation times, τθ and τJ, and analyzed the changes in the character of the rotational motion of the CH4 particles with a change in the composition of the mixture.

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