Phase diagrams and microstructure of aggregates in mixed ionic surfactant/foam booster systems

The phase behavior and microstructure of surfactant systems containing a new alkanolamide-type foam booster, dodecanoyl N-methyl ethanolamide (NMEA-12), were investigated by means of phase study and small angle X-ray scattering. Different from other similar alkanolamides, NMEA-12 possesses a low melting point and forms a lyotropic liquid-crystalline phase (L(alpha) phase) at room temperature. This is attributed to the attached methyl group, which increases the fluidity of the molecule. In the SDS/NMEA-12/water system, hexagonal and lamellar (L(alpha)) liquid-crystalline phases are obtained at significantly low surfactant concentrations. The stability of these phases decreases when SDS is replaced with a nonionic surfactant (C12EO8). However, for both ionic and nonionic surfactants, the effective area per surfactant molecule at the interface shrinks upon addition of NMEA-12, indicating that the surfactant layer is getting more compact. The possible implications of these results on the potential applications of NMEA-12 as foam stabilizer are discussed.