Mutable bubble surface mobility in water – propanol mixtures and its impact on bubble motion and deformation

Abstract

Various anomalies are typical for aqueous solutions of simple alcohols, with viscosity maxima and changing bubble surface mobility being significant for multiphase systems. Three regions of the hydrodynamic behaviour of spherical and ellipsoidal bubbles are described, depending on the propanol concentration. At low concentration (xP ≤ 0.005), alcohol behaves as a surfactant and the increase in concentration increases the drag coefficient and decreases bubble deformation. At intermediate concentration, the increase of concentration leads to more deformed bubbles with increasing rise velocity, because of the advantage of formation of bulk clusters. At high concentration (xP ≥ 0.07), bubbles behave as fully mobile with a low drag coefficient. Because of the fast desorption of molecules from the bubble surface, neither a concentration gradient nor a surface tension gradient arises, and thus the conditions for bubble surface mobility are fulfilled. The transition in the hydrodynamic behaviour is evident for all bubble sizes.