The dynamics of surface adsorption and foam formation of carbonate modified nonionic surfactants

For a group of nonionic surfactants with polar head groups synthesized by copolymerization of ethylene oxide and carbon dioxide, the adsorption dynamics at the water-air surface were investigated by dynamic surface tension measurements using the maximum bubble pressure technique. From the apparent diffusion coefficients at different concentrations, the diffusion coefficients of surfactant monomers and micelles were deduced and compared to conventional nonionic surfactants. These transport properties were correlated with results from foamability studies in Bartsch tests as well as sparging tests. The obtained foam volumes show a good correlation with the diffusion coefficients of the surfactant monomers multiplied with the concentration of available monomers, the cmc. The same relation is found for the foam stability, expressed in the foam half lifetime. The correlations show for surfactant solutions well above the critical micelle concentration that the transport of surfactant monomers to the interface rather than the micelles is the essential step in both, the foam formation as well as the foam stabilization, following a simple Fickian diffusion law.