Synthesis of alkyl polyamine with different functional groups and its montmorillonite swelling inhibition mechanism: Experiment and density functional theory simulation

In this work, low molecular weight alkyl polyamine (tris(2-methylaminoethyl)amine (TSA), hexamethyltris(2-aminoethyl)amine (TTA), nonamethyltris(2-aminoethyl)amine (TQA)) with different functional groups and the same hydrophobic chain was synthesized using tris(2-aminoethyl)amine (TPA). X-ray diffraction, scanning electron microscopy, X-Photoelectron spectroscopy, transmission electron microscopy, contact angle, and density functional theory simulation were used to investigate the montmorillonite swelling inhibition mechanisms. The results of the experiments showed that a small amount of TPA, TSA, TTA, and TQA can significantly reduce the basal spacing of montmorillonite (Mt). The basal spacing of montmorillonite did not change with increasing the inhibitor concentration. The basal spacing of Mt-TPA, Mt-TSA, and Mt-TTA had some differences in the dry and wet states, but there was no difference in Mt-TQA. This observation indicated that TPA, TSA and TTA exhibited a three-dimensional spatial configuration in the lamellar spacing of montmorillonite, while TQA was inserted into the space of montmorillonite layer in a single flat layer. As more amine groups were substituted by the methyl groups, the spatial configuration of inhibitors changes from a three-dimensional to a two-dimensional planar structure. The higher the number of hydrogen atom substitutions in the primary amine group by methyl groups, the larger the contact angle, and the stronger the hydrophobic capacity except for the quaternary ammonium groups. The simulation results indicated that the higher the number of substitutions, the larger the adsorption energy. Therefore, inhibitors with a quaternary amine group would have better inhibition performance.