ONE AND 2-COMPONENT ADSORPTION LAYERS OF N-HEXANE AND BENZENE ON GRAPHITE STUDIED BY H-2 NMR-SPECTROSCOPY

Deuteron (H-2) nuclear magnetic resonance (NMR) spectra were measured at temperatures between 300 and 90K for n-hexane (C6D14), benzene (C6D6), and a mixture of n-hexane and benzene (C6D14/C6H6 and C6H14/C6D6) adsorbed on the graphitized carbon black Carbopack B. The amounts adsorbed correspond to one monolayer coverage of each substance for both the single and the two-component adsorption. The single component layers each undergo a two-dimensional (2D) fluid/solid phase transition spread over a 30-40K interval centred at about the transition temperatures reported from diffraction studies. The surface diffusion coefficients in the 2D fluid regime are reported. On cooling to temperatures of about 200 to 160 K, three-dimensional benzene crystallites are formed leaving the n-hexane component in the one monolayer 2D fluid state. On further cooling, the n-hexane layer undergoes a 2D fluid/solid phase transition analogous to the corresponding one-component case.