The dilute solution behavior of sodium poly(styrene sulfonate) is studied in the presence of trivalent Al and bivalent Ba cations at various levels of excess NaCl. The study evaluates the phase behavior and the morphology of the polyelectrolyte chains with increasing extent of decoration with the Al and Ba cations and analyses the effect of temperature on these decorated chains. The phase behavior is presented in the form of the cation concentration versus the respective poly(styrene sulfonate) concentration, recorded at the onset of precipitation. Whereas poly(styrene sulfonate) with Al exhibits a linear phase boundary, denoted as the "threshold line," which increases with increasing poly(styrene sulfonate) concentration, Ba cations show a threshold line which is independent of the poly(styrene sulfonate) concentration. An additional re-entrant phase, at considerably higher cation content than those of the threshold lines, is observed with Al cations but not with Ba cations. The threshold line and the re-entrant phase boundary form parts of the liquid-liquid phase boundary observed at the limit of low polymer concentration. The dimensions of the polyelectrolyte chains shrink considerably while approaching the respective threshold lines on increase of the Al and Ba cation content. However, subtle differences occur between the morphological transformation induced by Al and Ba. Most strikingly, coils decorated with Al respond very differently to temperature variations than coils decorated with Ba do. As the temperature increases, the poly(styrene sulfonate) chains decrease their size in the presence of Al cations but increase in size in the presence of Ba cations.
A new class of viscoelastic surfactants for chemical enhanced oil recovery is presented. The triphenoxmethanes (TPM) show promise under harsh conditions of high salinity and high temperatures. The TPM's are viscoelastic at low concentrations (<0.5%w/w), show good stability in highly saline brine (18.6% TDS) that contains high concentrations of divalent cations at elevated temperatures (>70°C). Static adsorption measurements show acceptable values for the harsh conditions under study. Rheological measurements demonstrate that the viscoelasticity is not from formation of wormlike micelles and displays non-Maxwell behavior. We propose a novel supramolecular structure that explains the laboratory and rheological observations to date. The compounds show good injectivity into 2 Darcy Gildehaus sandstone The development of this class of compounds combines the efforts of a team comprised of synthesis, analytics, rheology, core lab and computational chemistry. The goal is to develop an understanding the system's behavior from the molecular level in-silico via computational chemistry, through coreflood tests -and beyond- for a future field pilot. The structure- property-relationships that are being developed will lead to further refinement and targeted development of next generation molecules with improved properties.
Dilute solutions of sodium poly(styrene sulfonate) (NaPSS) in the presence of Al, Ca, and Ba were analysed by means of isothermal titration calorimetry (ITC) in order to investigate the heat effect of bond formation between those cations and the anionic SO residues of NaPSS. The selection of the cations was guided by the solution behavior of the corresponding PSS salts from a preceding study [M. Hansch et al., J. Chem. Phys. 148(1), 014901 (2018)], where bonds between Ba and anionic PSS showed an increasing solubility with decreasing temperature and Al exhibited the inverse trend. Unlike to Al and Ba, Ca is expected to behave as a purely electrostatically interacting bivalent cation and was thus included in the present study. Results from ITC satisfactorily succeeded to explain the temperature-dependent solution behavior of the salts with Al and Ba and confirmed the non-specific behavior of Ca. Additional ITC experiments with salts of Ca and Ba and sodium poly(acrylate) complemented the results on PSS by data from a chemically different polyanion. Availability of these joint sets of polyanion-cation combinations not only offers the chance to identify common features and subtle differences in the solution behavior of polyelectrolytes in the presence of multi-valent cations but also points to a new class of responsive materials.
Sodium polyacrylate (NaPA) in dilute aqueous solution at an ionic strength of [NaNO3] = 0.01M establishes a rich phase behavior in the presence of low amounts of silver cations, which were introduced at a few millimoles or less by replacing the corresponding amount of Na+ cations. Beyond an extremely low level of Ag+ cations, anionic PA chains aggregate. By increasing the concentration of Ag+, the aggregates become denser and keep on growing without limit. Once a certain range of [Ag+] is reached, the instantaneously formed dense aggregates remain stable. Irradiation of the PA aggregate solutions with UV-light induces formation of silver nanoparticles (Ag-Nps). Based on a combination of UV-vis spectroscopy, light scattering, transmission electron microscopy, and small angle neutron scattering, the mechanism of this NaPA assisted formation of Ag-Nps is studied. One focus of the study is lying on the effect of the two different solution states of dense aggregates, corresponding to the unstable growing AgPA aggregates and to the stable AgPA aggregates and another focus is aiming at the characterisation of the morphology of the generated hybrid particles composed of Ag-Nps and hosting PA chains.
A new class of viscoelastic solutions -Triphenoxmethanes (TPM)-has been under development since early 2010 and remain a fruitful yet highly challenging research topic. The TPM's are viscoelastic at low concentrations (<0.5%w/w) and show good stability in highly saline hard brines. They have been tested in hard brines up to 25% TDS with high divalent cation concentration and show increasing performance with increasing salinity. The current lead candidate "TPM", which is also being scaled up for a first field trial, displays good performance to 75°C. Adsorption/retention measurements show quite acceptable values for the harsh conditions under study. Porous media testing has shown that the TPM's have good injectivity properties and mobilize significantly more oil than brine alone. In addition, oil displacement experiments with cores at residual oil concentration (Sor) have clearly shown that TPM mobilizes residual oil (ca.7% OOIP) without significant reduction of the IFT and with less than 1 PV injected fluid. The suitability for use in a particular reservoir is a complex interplay of the molecular structure of the TPM, temperature and brine salinity: lowering the salinity increases the application temperature. The interrelationship of the different factors is an on-going, high priority activity of the integrated R&D team. Here we report on the relevant aspects for application in harsh environments and give an outlook for field application.
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