Volumetric and Viscometric Studies on the Long Chain fatty acid in Surfactant Stabilized Propanol

Abstract

Volumetric and viscometric studies of binary mixtures of (fatty acid + propanol) and ternary mixtures of (fatty acid + propanol + surfactant) were done. Lauric, palm tic and stearic acids were taken as fatty acids while the surfactant was sodium dodecyl sulfate (SDS). The investigated binary and ternary systems were carried out over a concentration range of 0.0100-0.4000 M of fatty acids at 298.15 to 323.15 K at 5 K intervals. The SDS concentrations were 0.001 M and 0.005 M. The apparent molar volumes, φv. of both binary and ternary mixtures were determined from the densities of the mixtures. The φv, values have been found to be positive throughout the whole concentration range for all acids in propanol. The apparent molar volumes, .co. of all fatty acids in propanol were found to be increased with concentration at all temperatures.SimilarlyφV, values were found to be increased with increasing temperature at any concentration of the solution. These results may be due to the solute—solvent and solute—solute interaction in the solutions. This shows that φ, values are strongly dependent upon concentration as well as the temperature. The φv values are also found to be increased with the chain length of the fatty acids and this may be due to the hydrophobic characters of alkyl chain. The number of carbon atoms in the hydrocarbon chain of the fatty acid is proportional to the degree of hydrophobic/hydroPhilic balance of the whole compound. Eventually the pattern of apparent molar volumes of laurie, palmitic and stearic acids in 0.001 and 0.005 M SDS solution is very similar to those of (propanol + fatty acid) systems. The apparent molar volumes decreased at all concentration of SDS in comparison to corresponding systems without SDS. The results conferred that at molecular arrangements in SDS to (fatty acid+propanol) systems more organized than corresponding systems without SDS. The values of viscosity (η) of laurie, palmitic, and stearic acids in propanol increased with concentration at all six temperatures. The increase of η values of all acids with concentration can be attributed to the increase in both solute—solvent and solute—solute interactions with 17 are found to be increased with the carbon number along the hydrocarbon chain of the fatty acid concentration. At the same time, at a constant temperature and concentration, values of η. can be explained by the increase in both molecular mass of the fatty acid and the degree of solute solvent interactions with carbon number. The ultimate pattern of viscosity after addition of SDS is almost similar to corresponding systems without SDS. The change of free energy, ∆G and enthalpy, ∆H* values for viscous flow were found to be positive work had to be done to overcome the energy barrier for the flow process. The change of entropy, ∆S* values for the flow process are negative in all cases.