Studies on Volumetric and Viscometric Properties of Some iso-meric Alcohols in Surfactant Containing Ethanol Systems

Abstract

The critical micelle concentration (CMC) of Sodium Dodecyl Sulfate (SDS) in Ethanol was determined from the conductance, density and viscosity measurement. The estimated value of CMC was found to be 0.015 mol.L* The micellar concentration of SDS in Ethanol was used for the volumetric and viscornetric measurements of n-Propanol, iso-Propanol, n-Butanol, isoButanol, n-Pentanol and iso-Pentanol at different temperatures.

Densities and viscosities of ternary mixtures of n-Propanol in 0.015M SDS+Ethanol, isoPropanol in 0.015M SDS+Ethanol, n-Butanol in 0.015M SDS+Ethanol, iso-Butanol in 0.015M SDS+Ethanol, n-Pentanol in 0.015M SDS+Ethanol and iso-Pentanol in 0.015M SDS+Ethanol have been studied over the entire range of composition (0 <x2 <1) at 298.15323.15K with an interval of 5K. The density of alcohols in equi-molefraction of 0.015M SDS+Ethanol was found to be order of n-Pentanol n-Butanol > n-Propanol and iso-Pentanol> iso-Butanol > iso-Propanol.

The value of density of alcohols in 0.015M SDS+Ethanol decreases with the increasing of composition of the alcohols. The decrease of density with composition of alcohols can be - attributed to dissociation of components. The densities of all alcohols increase with the increase of carbon number which may be depend on the molecular weight of alcohols, structural formula and H-bonding of alcohols. The densities decrease regularly with the increasing of temperature. This is due to the thermal agitation and hence the weaker the dipole-dipole interaction or dissociation of H-bonding are occurred.

The excess molar volumes,VE were calculated from the densities of the mixtures at different temperatures. The values of VE for all the systems are positive over the entire range of composition, showing maxima 0.5 mole fraction of n-Propanol and - 0.5-0.6 mole fraction of iso-Propanol, 0.5-0.6 mole fraction of n-Butanol, --0.6 mole fraction of iso-Butanol, - 0.7-0.8 mole fraction of n-Pentanol and —0.8 mole fraction of iso-Pentanol. The excess molar volume, VE of alcohols in 0.015M SDS+Ethanol solutions was found to be order of n-Pentanol >n-B utanol >n-Propanol and iso-Pentanol >iso-Butanol >iso-Propanol and iso-Pentanol > n-Pentanol, iso-Butanol > n-Butanol and iso-Propanol > n-Propanol.The increasing of V with carbon chain length of alcohol may be related to increase of the size of alcohols. The values of [VE for the studied alcohols increase with the increase of temperature. The observed values of VE for the mixtures have been explained in terms of physical, chemical and geometrical contributions.

The viscosity coefficients, r7 of all the above mixtures at all the six different temperatures have also been determined. The viscosities increase slowly up to entire mole fraction of nPropanol,iso-Propanol. For n-Butanol and iso-Butanol, the viscosities increase initially slowly up to -0.6 mole fraction and later on, the viscosity increases sharply until the pure alcohol is reached.. For n-Pentanol and iso-Pentanol, the viscosities increase initially slowly up to -0.8 mole fraction and later on, the viscosity increases very sharply until the pure alcohol is reached. In pure state the viscosity of alcohols has been found to be in the order of, iso-Pentanol >n-Pentanol> iso-Butanol > n-Butanol> iso-Propanol n-Propanol The increasing of viscosity with carbon number of alcohols ascribed that the solution > resistance increases with the increase of carbon chain length. There is a marked decrease in the viscosity with increase of temperature for all the studied alcohols. This ascribed that the alcohol solutions are less stable at higher temperature. The linear dependence of In)7 againstl/T shows for the all studied alcohols. The branched chain isomers are less stable than linear chain isomer at higher temperature.The excess viscosity, 77E values are found to be negative, indicating that the 0.015M SDS + Ethanol solution of alcohols are non ideal. Excess viscosities are negative at all thetemperatures over the entire range of composition for all the systems with minima occurring between 0.6-0.8 mole fraction of n-Propanol, iso-Propanol, n-Butanol, iso-Butanol, n- Pentanol and iso-Pentanol. The negative excess viscosity, rf of 0.015M SDS+Ethanol + All the studied alcohols indicate that the dissociation of components through dispersive forces or steric hindrance. The position of minima virtually does not change remarkably with the variation of temperature. The values of the minima are in the order:

n-Pentanol>n-Butanol> n-Propanol and iso-Pentanol> iso-Butanol > iso-Propanol

The hydrophobic effect increases with the increasing of carbon chain length of alcohols. This indicates that the ηE decreases with the decrease of carbon number. The positive VE, negative ηF and negative & for the 0.015M SDS+Ethanol + studied alcohols systems indicate that dispersion force is dominant.

The thermodynamic parameters such as free energy (∆G), enthalpy (∆H) and entropy (∆S) change of activation for the viscous flow for these systems were examined for the entire range of composition. 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 negative excess free energy, ∆G indicate that the strong dispersion force in alcohols+ 0.01 5M SDS+Ethanol solution is dominant. The excess properties (VEηE ∆G*E) data have been fitted by the least square method to the four parameter Redlich-Kister equation and the values of the parameter a j and standard deviation have been reported. The volumetric properties are fully consistent with viscometric and thermodynamic properties.