Studies on CMC and thermodynamic function of anionic surfactants in DMA/long-chain alcohol systems using microcalorimetric method

摘要

The critical micelle concentration (CMC) and the thermodynamic function of the anionic surfactant, sodium laurate (SLA) and sodium dodecyl sulfate (SDS) in the N,N-dimethyl acetamide (DMA)/long-chain alcohol systems were studied using titration microcalorimetric method. The power-time curves of SLA and SDS in the presence of a long-chain alcohol (n-heptanol, n-octanol, n-nonanol, n-decanol) in the DMA medium were deter-mined. Then, from the curves, the critical micelle concentration (CMC) and the thermodynamic standard formation functions (△Hθm, △Gθm and △Sθm) were obtained through thermodynamic theories. The relation-ships between temperature, alcohol's carbon number, concentration and thermodynamic properties were dis-cussed. For SLA or SDS in a DMA solution, under the same concentration of alcohol, the values of CMC, △Hθmand △Sθm increase, while the values of △Gθm decrease with the increase of temperature. Under the same condition of identical temperature and alcohol concentration, the values of CMC, △Hθm, △Gθm and △Sθm decrease with the increase of the alcohol's carbon number. In the presence of the same kind of alcohol, the values of CMC and △Gθm increase, but the values of △Hθm and △Sθm decrease with the concentra-tion increases in alcohol series at the same temperature.