Experimental Study on Van der Waals Interactions Between Organic Groups of Quaternary Ammonium Salt Surfactants and Montmorillonite in Aqueous Solutions

Obtaining the dielectric constant and refractive index of the siloxane surface of montmorillonite (Mnt) and organic groups is difficult, limiting the study of Van der Waals (VDW) interactions between the hydrophilic end of quaternary ammonium surfactants (QASs) and Mnt. In this study, the average adsorption distance, VDW adsorption energy, and VDW constant of QASs and their groups adsorbed on the montmorillonite surface are obtained by microcalorimeter. Herein, the VDW interactions between five QASs and a Mnt surface are compared. Interactions between QASs with different hydrophilic ends and Mnt in aqueous solution were positively correlated with the dipole moment of the hydrophilic end groups, and the VDW interaction energies differed depending on the superposition of CH2 adsorption at the hydrophobic ends. The electrostatic and VDW adsorption capacities were studied through zeta potential and adsorption capacity experiments. Physical adsorption was determined using Fourier-transform infrared spectroscopy, and the hydrophobic floc morphology was characterized using environmental scanning electron microscopy. Focused beam reflectance measurements, thermogravimetric-differential scanning calorimetry, and light transmittance were used to quantitatively analyze the hydrophobic effect of the QASs.