Influence of Size and Surface Functionality of Surface-Modified Colloidal Silica Nanoparticles on Oil Wax Deposition Inhibition

This study investigated the impact of silica nanoparticle (SiNP) size (ranging from 10 to 90 nm) and surface functionalization on wax deposition inhibition. SiNPs were synthesized via a controlled sol–gel method and characterized using SEM, XRD, and BET. Two quaternary ammonium surfactants, cetrimonium bromide (CTAB) and benzalkonium chloride (BAC), were direclty grafted onto the SiNP surfaces at room conditions. The functionalized nanoparticles were analyzed using FTIR, TGA, and DLS to confirm the functional groups, surfactant loading, and stability, respectively. Surface adsorption isotherms were used to fix surfactant loading at 0.15 mg/m 2 to isolate the effect of nanoparticle size on the inhibition performance. Results showed that BAC was more effective for grafting than CTAB, likely due to stronger adsorption mechanisms, probably involving of π-cloud interactions between aromatic functional groups and SiNP surface silanol hydroxyls. Smaller nanoparticles possessing higher specific surface areas demonstrated superior performance in interacting with wax crystals. BAC-grafted nanoparticles were particularly effective at reducing the oil gelation point and yield strength. Notably, the addition of 10 nm BAC-grafted SiNPs at a low concentration of 100 ppm reduced the oil gelation point ( T g ) by 9 ± 0.7 °C and the deposit yield strength by 53%. The study proposed the critical role of nanoparticle electronegativity and surface compatibility in effectively interacting with and dispersing wax crystals to form finer, segregated crystal structures.