Asphaltene Adsorption onto Self-Assembled Monolayers of Alkyltrichlorosilanes of Varying Chain Length
Daniel A. Fischer, Saloman Turgman-Cohen, P K. Kilpatrick, Jan Genzer
The adsorption of asphaltenes onto flat silica surfaces modified with self-assembled monolayers (SAMs) of alkyltrichlorosilanes of varying thickness due to a variable number of carbon atoms (NC) has been studied by means of contact angle measurements, spectroscopic ellipsometry and NEXAFS spectroscopy. The extent of asphaltene adsorption was found to depend primarily on the ability of the SAM layer to shield the underlying silicon substrate from interacting with the asphaltenes present in solution. Specifically, asphaltene adsorption decreased with increasing SAM grafting density, SAM, (i.e., number of SAM molecules per unit area), or/and NC. The effect of solvent quality on the extent of asphaltene adsorption was gauged by adsorbing asphaltenes from toluene, 1-methylnaphthalene, tetralin, decalin and toluene/heptanes mixtures. The extent of asphaltene adsorption was found to increase proportionally with decreasing the Hildebrand solubility parameter of the solvent.