Interactions between mineral surfaces and organic molecules are fundamental to life processes. The presence of cations in natural environments can change the behavior of organic compounds and thus alter the mineral-organic interfaces. We investigated the influence of Na, Mg, Ca, Sr, and Ba on the interaction between two models, self-assembled monolayers, that were tailored to have hydrophobic -CH or hydrophilic -COO(H) terminations. Atomic force microscopy in chemical force mapping mode, where the tips were functionalized with the same terminations, was used to measure adhesion forces between the tip and substrate surfaces, to gather fundamental information about the role of these cations in the behavior of organic compounds and the surfaces where they adsorb. Adhesion force between hydrophobic surfaces in 0.5 M NaCl solutions that contained 0.012 M divalent cations did not change, regardless of the ionic potential, that is, the charge per unit radius, of the cation. For systems where one or the other surface was functionalized with carboxylate, -COO(H), mostly in its deprotonated form, -COO, a reproducible change in the adhesion force was observed for each of the ions. The trend of increasing adhesion force followed the pattern: Na ≈ Mg < Sr < Ca < Ba, suggesting that ionic potential, thus hydrated radius, controls the interaction. The presence of a -CH surface in the asymmetric system leads to lower adhesion forces than in the hydrophilic system, whereas the ionic trend remains the same. Although specific ion effects are felt in both systems, the lower adhesion force in the asymmetric system, compared with the hydrophilic system, implies that the -CH surface plays an important role.

The effectiveness of low salinity flooding for enhanced oil recovery (EOR) in sandstone reservoirs has been demonstrated in core plug and field tests as well as at molecular scale, but in carbonate reservoirs the results are mixed. With atomic force microscopy (AFM) chemical force mapping (CFM), using a methyl (CH3) functionalized tip, we tracked the wettability of limestone pore surfaces (before and after solvent treatment) during exposure to high and low salinity solutions at a submicrometer scale. The correlation between adhesion and salinity was weak for both the treated and the fresh samples, but detailed analysis of the force maps demonstrated that on the fresh limestone there are areas that clearly respond to changes in salinity. Adhesion decreased when salinity decreased on some areas, and on others adhesion increased. To understand this behavior, we analyzed the surfaces with X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDXS). The amount of organic material on the solvent treated samples was lower than on the fresh samples, but the amount and type of organic compounds were considerably different. These differences provide a likely explanation for the differences in the effectiveness of low salinity flooding that have been reported in the literature and lead us to conclude that for the samples analyzed in our study, the response in carbonate rocks is controlled by an intricate interplay between the composition of the tightly adsorbed organic material, the minerals on which it is adsorbed, and the functional groups present in the oil. Consequently, if the effectiveness of low salinity flooding in carbonate reservoirs is to be predicted, characterization of the organic compounds in the oil and on the pore surfaces is essential.

Pyrolytic carbon microelectrodes (PCMEs) are a promising alternative to their conventional metallic counterparts for various applications. Thus, methods for the simple and inexpensive patterning of PCMEs are highly sought after. Here, we demonstrate the fabrication of PCMEs through the selective pyrolysis of SU-8 photoresist by irradiation with a low-power, 806 nm, continuous wave, semiconductor-diode laser. The SU-8 was modified by adding Pro-Jet 800NP (FujiFilm) in order to ensure absorbance in the 800 nm range. The SU-8 precursor with absorber was successfully converted into pyrolytic carbon upon laser irradiation, which was not possible without an absorber. We demonstrated that the local laser pyrolysis (LLP) process in an inert nitrogen atmosphere with higher laser power and lower scan speed resulted in higher electrical conductance. The maximum conductivity achieved for a laser-pyrolyzed line was 14.2 ± 3.3 S/cm, with a line width and thickness of 28.3 ± 2.9 µm and 6.0 ± 1.0 µm, respectively, while the narrowest conductive line was just 13.5 ± 0.4 µm wide and 4.9 ± 0.5 µm thick. The LLP process seemed to be self-limiting, as multiple repetitive laser scans did not alter the properties of the carbonized lines. The direct laser writing of adjacent lines with an insulating gap down to ≤5 µm was achieved. Finally, multiple lines were seamlessly joined and intersected, enabling the writing of more complex designs with branching electrodes and the porosity of the carbon lines could be controlled by the scan speed.