Ultrasonic, volumetric and viscometric studies of lactose in mixed solvent of DMF-H2O at 298, 308 and 318Â K

Acoustic parameters are useful to understand the effect of temperature on the interactions of lactose in mixed solvent of (DMF-H2O). Density (ρ), viscosity (η), sound speed (u) and refractive index (nD) of lactose with mixed solvent of N,N-dimethylformamide-water or (DMF-H2O) from 0.1050 to 1.045 m at different temperatures have been determined using bicapillary pycnometer, Ostwald's viscometer, Abbe's refractometer and single frequency ultrasonic interferometer at 2 MHz frequency respectively. The derived parameters like apparent molal volume (ϕv), free volume (Vf), intermolecular free length (Lf), acoustic relaxation time (τ), Gibb's free energy (ΔG), internal pressure (πi), Rao's constant (Rm), Wada's constant (W), adiabatic compressibility (β), acoustic impedance (Z), absorption coefficient (α/f2) and molar refractivity (RD) have been determined from experimental data. All the measurements have been carried out in a refrigerated water bath with circulating medium having an uncertainty of ±0.1 °C. Positive values of the Jones-Dole coefficient (B) indicate structure making tendency. The solute-solvent interactions are stronger at all the temperatures taken for the study.