Synergistic adsorption of mixtures of cationic gemini and nonionic sugar-based surfactant on silica

Adsorption behavior of cationic C12-C4-C12C12-C4-C12 gemini surfactant on silica has been investigated, along with that of nonionic surfactant n-dodecyl-β-d-maltoside (DM). While DM alone shows meager adsorption on silica, because of the lack of any electrostatic adsorption, cationic gemini adsorbs significantly on the oppositely charged silica surface. Due to the electrostatic nature of cationic gemini adsorption on silica, solution pH affects adsorption of C12-C4-C12C12-C4-C12 gemini dramatically. Meanwhile, C12-C4-C12C12-C4-C12 gemini hemimicelle size at silica/water interface does not seem to change with solution pH. For the mixtures of DM and cationic C12-C4-C12C12-C4-C12 gemini, there is a sharp increase of DM adsorption at silica/water interface, up to 100 times more than DM alone. After mixing with DM, saturation adsorption of cationic C12-C4-C12C12-C4-C12 gemini decreases, due to competition for adsorption sites from DM. At the same time, in its mixture with DM, there is an increased adsorption of C12-C4-C12C12-C4-C12 gemini in the rising part of the adsorption isotherm. Hydrophobic chain–chain interactions, especially with two hydrophobic chains in one C12-C4-C12C12-C4-C12 gemini molecule, and adsorbed C12-C4-C12C12-C4-C12 gemini molecule acting as an anchor or nucleation sites for forming mixed aggregates with DM on silica surface, are attributed to the marked adsorption synergy between DM and cationic C12-C4-C12C12-C4-C12 gemini. The adsorption of surfactants and their mixtures has a marked effect on silica surface charge and silica's wettability.

Enhanced nonionic n-dodecyl-β-d-maltoside (DM) adsorption by synergistic adsorption with cationic gemini surfactant from their mixtures on silica surfaces.Figure optionsDownload as PowerPoint slide