Investigation of the Precipitation Behavior of Asphaltenes in the Presence of Naphthenic Acids Using Light Scattering and Molecular Modeling Techniques

A delay in the onset of flocculation is observed for asphaltenes in the presence of several naphthenic acids: methyl abietate, hydrogenated methyl abietate, 5β-cholanic acid, and 5β-cholanic acid-3-one. This flocculation behavior is monitored as a function of the added precipitant (<i>n</i>-heptane) to solutions of suspended asphaltenes and naphthenic acids in model solutions of toluene/<i>n</i>-heptane, using a combination of dynamic light scattering (DLS) and near-infrared (NIR) spectroscopic techniques. DLS and NIR show very good correlation in indentifying the onsets of flocculation, which varied among the series of naphthenic acids. Specific interaction energies and equilibrium intermolecular distances of asphaltenes and naphthenic acids are calculated using molecular mechanics. The results from molecular mechanics calculations support the experimental results of the titrations, and structure–property relationships are defined. Structure–property relationships are established for naphthenic acids, defining the relative contributions and importance of various functional groups: CC, CO, COOR, and COOH. The additive effects of naphthenic acids, defined by an increase in the precipitation onset, increase in the order of 5β-cholanic acid-3-one < hydrogenated methyl abietate < methyl abietate < 5β-cholanic acid, with experiments containing 5β-cholanic acid-3-one containing unexpected and interesting results

Preparation and Characterization of Polyhedral Oligomeric Silsesquioxane-Containing, Titania-Thiol-Ene Composite Photocatalytic Coatings, Emphasizing the Hydrophobic–Hydrophilic Transition

Coatings prepared from titania-thiol-ene compositions were found to be both self-cleaning, as measured by changes in water contact angle, and photocatalytic toward the degradation of an organic dye. Stable titania-thiol-ene dispersions at approximately 2 wt % solids were prepared using a combination of high-shear mixing and sonication in acetone solvent from photocatalytic titania, trisilanol isobutyl polyhedral oligomeric silsesquioxane (POSS) dispersant, and select thiol-ene monomers, i.e., trimethylolpropane tris­(3-mercaptopropionate) (TMPMP), pentaerythritol allyl ether (APE), and 1,3,5-triallyl-1,3,5-triazine-2,4,6­(1<i>H</i>,3<i>H</i>,5<i>H</i>)-trione (TTT). The dispersed particle compositions were characterized by DLS and TEM. The synthetic methods employed yield a strongly bound particle/POSS complex, supported by IR, ²⁹Si NMR, and TGA. The factors of spray techniques, carrier solvent volatility, and particle size and size distributions, in combination, likely all contribute to the highly textured but uniform surfaces observed via SEM and AFM. Polymer composites possessed thermal transitions (e.g., <i>T</i>_g) consistent with composition. In general, the presence of polymer matrix provided mechanical integrity, without significantly compromising or prohibiting other critical performance characteristics, such as film processing, photocatalytic degradation of adsorbed contaminants, and the hydrophobic–hydrophilic transition. In all cases, coatings containing photocatalytic titania were converted from superhydrophobic to superhydrophilic, as defined by changes in the water contact angle. The superhydrophilic state of samples was considered persistent, since long time durations in complete darkness were required to observe any significant hydrophobic return. In a preliminary demonstration, the photocatalytic activity of prepared coatings was confirmed through the degradation of crystal violet dye. This work demonstrates that a scalable process can be found to prepare titania-thiol-ene coatings having improved coating properties which also exhibit photocatalytic and self-cleaning attributes