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Thermodynamical Investigation of Aqueous Sodium Dodecyl Sulphate: Comparison of the Fillers Sodium Chloride and Sodium Sulphate


Detergent is an aggregation of surfactants, builders, fillers by enabling the solution to wet a surface quickly and effectively. It also emulsifies oily soils and keep them, bleaches, dyes, enzymes and several other ingredients. Surfactants cleanses suspended and dispersed so they do not settle back on the surface. To achieve superior cleaning performance, other compounds like builders and fillers are added to surfactants. Sodium dodecyl sulphate is an anionic surfactant, primary ingredient added to detergents and cleaning products. In the present investigation, the molecular interactions of SDS are studied through the addition of fillers sodium chloride and sodium sulphate. The important usage of NaCl and Na2SO4 are in the manufacture of detergents. Sodium sulphate is a very cheap material, consuming approximately about 50% of world production. It helps in “leveling”, reducing negative charges on fibers so that dyes can penetrate evenly on fabrics. Similarly sodium chloride also serves as effective filler when added to SDS. The efficiency of these SDS and fillers in detergent action can be analyzed by the thermo dynamical study using ultrasonic method with the measurement of ultrasonic velocity, viscosity and density. Using the measured values, thermo dynamical parameters like internal pressure, free volume, osmotic pressure, Δπi, Gibb’s free energy, molar cohesive energy were evaluated for aqueous SDS with fillers at different temperatures. Ultrasonic study of the aqueous solutions reveals some information regarding internal pressure which is a single factor appears to vary due to the internal cohesive forces resultant from attractive and repulsive forces between the molecules. It measures the molecular cohesion and instantaneous volume derivative of cohesive energy associated with an isothermal expansion of solutions. The internal pressure of hydrogen bonded liquids (water) is large as compared to nonhydrogen bonded liquids. Hence it can be used for studying molecular association of hydrogen bonding. Similarly free volume is one of significant factor in explaining the free space and its dependent properties have close connection with molecular structure and it may show features about various interactions. It seems to be conditioned by repulsive forces whereas internal pressure is sensitive to attractive forces. Gibb’s free energy is the energy associated with a chemical reaction that can be used to do work. Molar cohesive energy is arising due to the mutual attractiveness of molecules. Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of solvent molecules across a semipermeable membrane. Various interactions of SDS with fillers are explained in terms of above parameters and also the relationships πi=π0+Am2+Bm for internal pressure and Vf=Vf0+Cm2+Dm for free volume were also verified. Thecoefficients A, B and C, D for the above equation have been calculated at different temperatures. Δπi gives an idea about the effect of cohesive forces in ion-solvent interaction. It is understood that sensitive information regarding the cohesive forces is well obtained by the data Δπi instead of the coefficients of the above equation.

Renuka DK, Gomathiyalini A

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