1H NMR longitudinal relaxation times (T1, exp of the hydroxyl and methyl group) of methanol in supercritical and subcritical gas-like and liquid-like CO2+methanol mixtures were obtained as a function of pressure up to 25 MPa and at 293.15 and 308.15 K, respectively. This study was designed to investigate the mechanism of the spin-lattice relaxation (SLR) time T1 in different phase regions of CO2+methanol as homogenous gas-like, and liquid-like mixtures, and the influence of pressure, temperature, and composition on the relaxation rate was examined. Moreover, the density dependent isotherms of the SLR rates 1/T1, exp were comparatively studied between gas-like and liquid-like binary mixtures. There exists an obvious phase dependent SLR mechanism within the temperature and pressure range carried out herein, that is, the SLR process is dominated by the dipole-dipole (DD) interaction mechanism for both liquid-like mixture and methanol, whereas by the spin-rotation (SR) mechanism for gas-like mixture. Measurement of nuclear magnetic relaxation times can offer micro-dynamic and micro-structural information and are very useful for the study of fluids of strongly interacting molecules. Mutual influence of electric dipoles as well as hydrogen bonds helps determine the structure of the fluid and its molecular dynamics. The present work increases our knowledge of molecular dynamics of alcohols in sub-and supercritical CO2.
Fund: the National Natural Science Foundation of China(21543009);the National Natural Science Foundation of China(21073167);the National Natural Science Foundation of China(J1210060);Innovative Research Grant for Undergraduate Students of National/Zhengzhou University, China(201410459047);Innovative Research Grant for Undergraduate Students of National/Zhengzhou University, China(201510459046);Innovative Research Grant for Undergraduate Students of National/Zhengzhou University, China(2016xjxm259)
Xiao-Meng CHENG,Yu LI,Zong CHEN,Hong-Ping LI,Xiao-Fang ZHENG. A Comparative Study on theNMR Relaxation of Methanol in Sub-and Super-Critical Mixtures of CO2 and Methanol. Acta Physico-Chimica Sinca, 2016, 32(11): 2671-2677.