Packing and conformational contributions in binary liquid mixtures. Acoustic studies of n-hexadecane with dimethylpentanes

Abstract

In order to separate internal (rotational isomeric) and external (intermolecular structural) contributions to volume effects in liquid alkane mixtures, ultrasonic attenuation and velocity measurements have been made on hexadecane and its mixtures with dimethylpentane. Within experimental error the rotational isomeric contribution is a simple sum of those of the pure components. However, the shear and volume viscosity contributions are not linearly additive, but show a negative excess quantity. This is explained on the basis of a structural equilibrium between more ordered (solid-like) and less ordered (more liquid-like) regions in the liquid mixture. The results indicate that there is a geometrical packing component in the mixture interaction parameter, χ₁₂.