An Electrode-Separated Piezoelectric Sensor as a Surface Monitoring Technique for Anionic Surfactant Adsorption on Quartz Surface

Abstract

In the configuration of an electrode-separated piezoelectric sensor (ESPS), the quartz crystal surface is in a direct contact with the liquid phase. With the pre-adsorption of Ca2+ as the ionic bridge, anionic surfactant can adsorb on the negatively charged quartz surface (pH > 2.0). The adsorption process of sodium dodecyl benzenesulfonate (SDBS) was monitored in real time with the ESPS method. It was shown that the adsorption of SDBS on quartz surface by Ca2+ inducement was reversible with respective to the dilution of solution phase. The adsorption behavior can be analyzed using Langmuir model. The adsorption and desorption rate constants were estimated to be ka = (108.4 ± 6.4) mol−1L s−1 and kd = (2.57 ± 0.32) × 10−3 s−1, respectively. The observed adsorption densities in the ESPS method were significantly greater than the true ones. The influence on surface roughness of the quartz disc on adsorption densities should be corrected by adding a calibration coefficient in the Sauerbrey equation. The saturation adsorption density is 0.223 µg/cm2 for SDBS on quartz surface. Double layer occurs for the adsorption of SDBS on quartz surface.