Controlling Aggregation of Nonionic Surfactants Using Mixed Glycol Media

The extent of aggregation of nonionic surfactants can be controlled by the composition of mixed solvents with two miscible glycols, ethylene glycol (EG)/propylene glycol (PG). Three nonionic surfactants bearing a common E8 ethoxylated headgroup, but with variations in the hydrocarbon chain, have been investigated:  octaethylene monododecyl ether (C12E8), octaethylene monotetradecyl ether (C14E8), and octaethylene monohexadecyl ether (C16E8). The hydrogen-bonding solvents were EG/PG mixtures at different PG levels, defined in terms of the concentration (mol %) of PG. Aggregation was investigated using small-angle neutron scattering (SANS) with h-CiE8 surfactants, at 10 and 5 wt %, in deuterated glycol solvents to improve contrast. Increasing PG concentration (mol %) in the background EG/PG solvent leads to a consistent decrease in the SANS intensity, until in pure d-PG only very weak scattering is observed. These SANS data were analyzed using cylinder or ellipsoidal form factors for the EG-rich and PG-rich systems, respectively, hence demonstrating an aggregate shape change as a function of solvent composition. The results show that aggregation of nonionic surfactants occurs in glycol solvents and that the EG:PG ratio may be used as an effective means to switch aggregation “on” or “off”, as required.