Pyromellitic-Based Low Molecular Weight Gelators and Computational Studies of Intermolecular Interactions: A Potential Additive for Lubricant

Abstract

Low molecular weight gelators (LMWG) have been extensively explored in many research fields due to their unique reversible gel-sol transformation. Intermolecular interactions between LMWG are known as the main driving force for self-assembly. During this self-assembly process, individually analyzing the contribution difference between various intermolecular interactions is crucial to understand the gel properties. Herein, we report 2,5-bis(hexadecylcarbamoyl)terephthalic acid (<b>BHTA</b>) as a LMWG, which could efficiently form a stable organogel with <i>n</i>-hexadecane, diesel, liquid paraffin, and base lubricant oil at a relatively low concentration. To investigate the contribution difference of intermolecular interactions, we first finished FT-IR spectroscopy and XRD experiments. On the basis of the <i>d</i>-spacing, a crude simulation model was built and then subjected to molecular dynamics (MD) simulations. Then, we knocked out the energy contribution of the H-bonding interactions and π-π stacking, respectively, to evaluate the intermolecular interactions significantly influencing the stability of the gel system. MD simulations results suggest that the self-assembly of the aggregates was mainly driven by dense H-bonding interactions between carbonyl acid and amide moieties of <b>BHTA</b>, which is consistent with FT-IR data. Moreover, wave function analysis at a quantum level suggested these electrostatic interactions located in the middle of the <b>BHTA</b> molecule were surrounded by strong dispersion attraction originating from a hydrophobic environment. Furthermore, we also confirmed that 2 wt % <b>BHTA</b> was able to form gel lubricant with 150BS. The coefficient of friction (COF) data show that the gel lubricant has a better tribological performance than 150BS base lubricant oil. Finally, XPS was performed and offered valuable information about the lubrication mechanism during the friction.