No abstract

The adsorption of surfactants (DTAB, SDS, and CAPB) at the calcite-water interface was studied through surface zeta potential measurements and multiscale molecular dynamics. The ground-state polarization of surfactants proved to be a key factor for the observed behavior; correlation was found between adsorption and the hard or soft charge distribution of the amphiphile. SDS exhibits a steep aggregation profile, reaching saturation and showing classic ionic-surfactant behavior. In contrast, DTAB and CAPB featured diversified adsorption profiles, suggesting interplay between supramolecular aggregation and desorption from the solid surface and alleviating charge buildup at the carbonate surface when bulk concentration approaches CMC. This manifests as an adsorption profile with a fast initial step, followed by a metastable plateau and finalizing with a sharp decrease and stabilization of surface charge. Suggesting this competition of equilibria, elicited at the CaCO3 surface, this study provides atomistic insight into the adsorption mechanism for ionic surfactants on calcite, which is in accordance with experimental evidence and which is a relevant criterion for developing enhanced oil recovery processes.

The PC-SAFT equation of state was applied to the study of RAFT polymerization of methyl methacrylate in supercritical CO2.

A free-radical inverse emulsion polymerization formulation has been developed for preparation of acrylamide (AAm)/sodium 2-acrylamido-2-methylpropanesulfonate (AMPSNa)/N-vinylpyrrolidone (VP) terpolymers. An aqueous solution of a blend of monomers is emulsified in ndecane using Tween 85 (Tw85). Ammonium persulfate (APS) and dicumyl peroxide (DCP) were used as initiators for water and oil phases, respectively. The reactions were catalyzed by temperature and by a redox pair; the former is achieved at 608C and the latter by adding tetramethylethylenediamine (TEMED) and sodium bisulphite (BisNa) to activate the initiator in water and oil phase, respectively. The emulsion type, stability, conversion, and rate of polymerization were analyzed. The obtained terpolymer was characterized by elemental analysis, infrared spectroscopy (FTIR), 13 C nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and rheology. Thermal catalyzed emulsion polymerization initiated with DCP showed the best performance as viscosity control agent and as polymeric precursor for in situ gel forming, for water mobility control and flow diversification, respectively. Both application for enhanced oil recovery purposes in harsh oil reservoir conditions are presented.