Viscous synergy of pure monoalcohol mixtures in water and its relation to concentration

Pure or aqueous alcohols are the solvents most widely used in industry, including in the manufacture of pharmaceuticals and cosmetic products. However, water-alcohol mixtures generate hydrogen-bonded molecular associations that lead to volume contraction and an increase in viscosity greater than that expected in the absence of any interaction between the components of the mixture. This phenomenon is referred to as viscous synergy. The present study investigates viscous synergy in monoalcohol systems containing up to five carbon atoms, since beyond hexanol all alcohols are practically insoluble in water. In all cases, determinations were made of the proportions of water and alcohol for which maximum viscosity is observed, together with the corresponding synergy index. An enhancement index has likewise been introduced, defined as: E-eta = D (eta(max)/eta(0)), where eta(max) is the maximum viscosity reached in the water-alcohol mixture, and eta(0) is the viscosity of the pure alcohol.