Journal of Chemical and Pharmaceutical Research (ISSN : 0975-7384)

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Original Articles: 2014 Vol: 6 Issue: 5

Comparative study of free volume and permeability coefficient of aqueous solutions of D-mannitol across cellulose acetate membrane at various temperatures.


Ultrasonic velocity has been measured in aqueous solutions of D-Mannitol at 6.0 MHz and at a temperature 303.15 K. The results are discussed in terms of different theories of propagation of ultrasonic waves. From the velocity, density and viscosity data values, various acoustical parameters namely, adiabatic compressibility(βad), intermolecular free length(Lf), free volume(Vf), Rao’s constant(R), Wada’s constant(W), relaxation time(τ), specific acoustic impedence(Z), classical sound absorption(α/f2 )class., internal pressure(πi), molar cohesive energy(MCE), relative association(RA), and solvation number(Sn) have been calculated. The values of free volume (Vf) so obtained were correlated with permeability coefficient (Lp) values of these aqueous solutions through cellulose acetate membrane at three different temperatures(303K, 308K, 313K). Various activation parameters namely enthalpy of activation(∆H*), entropy of activation(∆S*) and free energy of activation(∆G*) have been estimated which illustrates increased stability of these solution systems. The acoustical parameters have been discussed separately to throw light on the molecular association and formation of intermolecular hydrogen bonding between the hydroxyl groups of D-mannitol and water molecules. In light of hydrogen bonding, internal pressure and molar cohesive energy is used to study the close packing of molecules in solutions.The permeability coefficient (Lp) has been found to be independent of the hydraulic pressure but is a characteristic property of the membrane and depends on the concentration of the solute. The results showed that permeability coefficient (Lp)increases and free volume (Vf) decreases with increase in concentration and in both the cases the data is found to be in accordance with their observed density (ρ) and viscosity (η) data.