Wettability alteration of organo-vermiculites induced by layer charge and tailored bis-N-heterocyclic quaternary ammonium salts

Wettability is an important surface property that deserves to further explore the factors on its alteration. Series of bis-N-heterocyclic quaternary ammonium salts with different spacer length and N-heterocyclic headgroups (morpholinium (BMMB, BMMD and BMMH), piperidinium (BPMH) and piperazinium (BMPMH)) have been synthesized and employed for altering the wettability of vermiculite and its derivates (Vts) treated by Li+-saturated heating method. The results of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TG-DTG), scanning electron microscopy (SEM) and N-2 adsorption/desorption isotherms indicate that all of the bis-N-heterocyclic quaternary ammonium salts have been successfully inserted into the vermiculite layers, leading to the organic monolayer. The results of capillary rise tests combined with Lipophilic to Hydrophilic Ratio (LHR) values unveil the wettability alteration of the organo-Vts. As the layer charge decreases, the hydrophilicity of the organo-Vts gradually increases, which is probably caused by the decline in binding sites. As the result of the change in spacer length of modifier, the wetting properties of morpholinium-based organo-Vts change in order of BMMD-Vts > BMMH-Vts > BMMB-Vts, and difference in N-heterocyclic headgroups leads to the sequence of wettability: BMPMH-Vts > BPMH-Vts > BMMH-Vts. Layer charge of Vt, spacer length and the type of the N-heterocyclic headgroup of modifier have the synergistic effect on the regulation of the wettability.

Automated summary

Wettability is an important surface property that can be altered by various factors. In this study, a series of bis-N-heterocyclic quaternary ammonium salts were synthesized and used to modify the wettability of vermiculite and its derivatives. The results showed that the salts were successfully inserted into the vermiculite layers, resulting in the formation of an organic monolayer. The wettability was found to be influenced by the layer charge of the vermiculite, the spacer length of the modifier, and the type of N-heterocyclic headgroup.