Surface Activities of Nonionic Polymeric Surfactants

The relationship between surface activity and molecular structure has been studied for the nonionic polymeric surfactants which have 2,3,4 or 6 branches of polypropylene glycol-polyethylene glycol (PPG-PEG) chain in their molecules. A linear relation, 1⁄Δγ=A+B·x⁄y has been found to hold for each series, where Δγ is the surface tension depression of surfactant solution of a given concentration from that of water, x⁄y is the molecular structure index, in which x is the weight percent of PEG group in a molecule and y is the molar weight of PPG part, and A and B are constatns. Constant A, being equal to 0.025 cm/dyn, is independent of the concentration and the number of PPG-PEG branches and corresponds to the reciprocal of surface tension lowering of an aqueous solution of infinitely large PPG polymer. Constant B decreases linearly with the logarithm of molar concentration, and increases with the number of branches. It also depends on the hydrophilic nature of the central group of molecule.