Volumetric and Viscometric Studies Of Some Binary and Ternary Sodium Dodecyl Sulfate (SDS) Containing Alcohol System

Abstract

Densities and viscosities of binary mixtures of Methanol Propanol + Water and iso-Propanol + Water, Ethanol + Water, ii-0.005M and 0.01M aqueous SDS, Ethanol + 0.005M and 0.0IM aqueous SDS. n-Propanol ± 0.005M and 0.0IM aqueous SDS and iso-Propanol + 0.005M and 0.01M aqueous SDS have been studied over the entire range of composition (0 < X2 < + Water and ternary mixtures of Methanol I) at 298.15- 323.15K with an interval of 5K except methanol. Methanol system was studied at 298.15K, 303.15K and 308.15K The excess molar volumes, V' were calculated from the densities of the mixtures at different composition, showing minima at 0.45 mole fraction of Methanol, 0.4 mole fraction of Ethanol, 0.25 mole fraction of n-Propanol and 0.3 mole fraction of iso-Propanol. The VE for all the systems are negative over the entire range of temperatures. The values of values for the n-Propanol VE + Water and iso-Propanol + Water mixtures are sigmoids, being negative at lower mole fractions (X2) and positive at higher of Propanols. The magnitudes of the VL values of the mixtures are in the order: iso-Propanol X2 > Methanol Propanol. The observed values of V' for the mixtures have been explained in terms ofphysical, chemical, and geometrical contributions. The physical interactions, that is, nonspecific interactions between the real species present in the mixture, involve mainly dispersion force giving a positive contribution. The chemical or specific intermolecular interactions result in a volume decrease and these interactions include formation of hydrogen bonds and other complex-forming interactions. The structural contributions are mostly negative and arise from several effects, especially from interstitial accommodation and changes of free volume. The viscosity coefficients, il of all the above mixtures at all the six different temperatures have also been determined. Viscosities increase rapidly with alcohol concentration and show maxima in the water and aqueous SDS rich region at 0.2 - 0.3 mole fraction of alcohols. The position of maxima virtually does not change remarkably with the variation of temperature. the polar-polar mixtures, quite expectedly, show considerable deviation from ideal behavior. The excess viscosities, i/ values are found to be positive and large in magnitude, indicating that the aqueous and aqueous SDS solutions of alcohols are The hanol > ii-highly non ideal. All the curves pass through maxima in water and aqueous SDS rich region. The heights of the maxima are in the order:iso-Propanol + WaterPropanol + Water> Ethanol + Water> Methanol + The rapidly ascending part of viscosity curves in the dilute region of alcohols can be explained primarily in terms of the phenomenon called hydrophobic hydration, which assumes that, in water—rich region, the water molecules form highly ordered structures through hydrogen bonding around the hydrocarbon moieties of alcohols. The interaction parameter, have also been found to be positive in magnitude indicating strong solute-solvent interaction. The thermodynamic parameters such as, free energy (∆G#), enthalpy (∆H#) and entropy (∆S#) change of activation for the viscous flow of the binary and ternary systems are calculated for the entire range of composition by using Eyring's equation. The free energy (∆G#) were found to be positive in magnitude indicating that the kinetic species involved in forming cavities or holes in the liquid medium is given by the work required in forming the hole against surface tension of the solution. The excess properties (VE nE ∆GE) data have been fitted by the least square method to the four parameter Redlich-Kister equation and the values of the parameter a1 have been reported.The critical micelle concentration (CMC) of sodium dodecyl sulfate (SDS) in water was determined from the conductance and viscosity measurement. They shows a sharp break in their values where micelle starts to form and is determined by extrapolating the data in premicellar region to intersect with a straight line drawn through the data in the post-micellar region.The estimated value of CMC was found to be 0.0085 mol.L -1 at 290C. The concentration of SDS in pre-micellar and post-micellar region of 0.005M and 0.0IM were used for the volumetric, viscometric and thermodynamic measurements. Although the value of density and viscosity of the studied systems in pre-micellar and postmicellar aqueous SDS solutions (0.005M SDS and 0.0IM SDS) are higher than the pure water solutions, but no appreciable change in the volumetric and viscomctric properties were observed by the addition of the surfactants.