The study of surface dilational properties of nonionic surfactant solutions by propagation of electrocapillary waves

An efficient experimental technique for the study of dynamic surface dilational properties through electrocapillary waves has been developed. Surface waves at the air/liquid interface are generated with electrocapillary deflection and detected by specular reflection of a focused laser beam. Without contacting the surface, the capillary wavelengths and damping coefficients were measured and, thus, the surface moduli were determined in the frequency range of 50 to 500 Hz for various nonionic surfactants. We found that the dilational modulus in the entire submicellar range is frequency independent in this frequency range. This observation is consistent with the data obtained at low frequencies previously published in the literature. Above the CMC, the wavelengths and damping coefficients become constant with increasing concentration. This implies that the surface properties are essentially independent of concentration.