Star-Like Branched Polyacrylamides by RAFT polymerization, Part II: Performance Evaluation in Enhanced Oil Recovery (EOR)

In the present study the performance of a series of star-like branched polyacrylamides (SB-PAMs) has been investigated in oil recovery experiments to ultimately determine their suitability as novel thickening agent for enhanced oil recovery (EOR) applications. Hereby, SB-PAMs were compared with conventional linear PAM. The effect of a branched molecular architecture on rheology, and consequently on oil recovery was discussed. Rheological measurements identified unique properties for the SB-PAMs, as those showed higher robustness under shear and higher salt tolerance than their linear analogues. EOR performance was evaluated by simulating oil recovery in two-dimensional flow-cell measurements, showing that SB-PAMs perform approximately 3–5 times better than their linear analogues with similar molecular weight. The salinity did not influence the solution viscosity of the SB-PAM, contrarily to what happens for partially hydrolyzed polyacrylamide (HPAM). Therefore, SB-PAMs are more resilient under harsh reservoir conditions, which can make them attractive for EOR applications

Polystyrene–Poly(sodium methacrylate) Amphiphilic Block Copolymers by ATRP: Effect of Structure, pH, and Ionic Strength on Rheology of Aqueous Solutions

Three well-defined polystyrene–poly­(sodium methacrylate) amphiphilic block copolymers characterized by different molecular architecture (diblock, triblock, and four-arm star) have been synthesized by ATRP. The rheology of their water solutions has been evaluated by measuring dynamic moduli and shear viscosity at different concentrations. All polymers show remarkable thickening properties and a sol–gel transition at low concentration (0.1 wt %). Above the gel concentration the solutions are shear thinning without an apparent Newtonian plateau. The observed viscosity profile can be interpreted in terms of percolation theory applied to highly stretched polymeric micelles, which start to contract above the percolation threshold. An interesting correlation between solution viscosity and concentration of hydrophilic block (defined here as “arm concentration”) has been observed, giving indirect evidence for the arrangement of the polymers into micelles. The influence of ionic strength and pH on the rheology of these systems has also been preliminary investigated

Polystyrene–Poly(sodium methacrylate) Amphiphilic Block Copolymers by ATRP: Effect of Structure, pH, and Ionic Strength on Rheology of Aqueous Solutions

Three well-defined polystyrene–poly­(sodium methacrylate) amphiphilic block copolymers characterized by different molecular architecture (diblock, triblock, and four-arm star) have been synthesized by ATRP. The rheology of their water solutions has been evaluated by measuring dynamic moduli and shear viscosity at different concentrations. All polymers show remarkable thickening properties and a sol–gel transition at low concentration (0.1 wt %). Above the gel concentration the solutions are shear thinning without an apparent Newtonian plateau. The observed viscosity profile can be interpreted in terms of percolation theory applied to highly stretched polymeric micelles, which start to contract above the percolation threshold. An interesting correlation between solution viscosity and concentration of hydrophilic block (defined here as “arm concentration”) has been observed, giving indirect evidence for the arrangement of the polymers into micelles. The influence of ionic strength and pH on the rheology of these systems has also been preliminary investigated

Pickering Emulsions and Antibubbles Stabilized by PLA/PLGA Nanoparticles

Micrometer-sized double emulsions and antibubbles were produced and stabilized via the Pickering mechanism by colloidal interfacial layers of polymeric nanoparticles (NPs). Two types of nanoparticles, consisting either of polylactic acid (PLA) or polylactic-co-glycolic acid (PLGA), were synthesized by the antisolvent technique without requiring any surfactant. PLA nanoparticles were able to stabilize water-in-oil (W/O) emulsions only after tuning the hydrophobicity by means of a thermal treatment. A water-in-oil-in-water (W/O/W) emulsion was realized by emulsifying the previous W/O emulsion in a continuous water phase containing hydrophilic PLGA nanoparticles. Both inner and outer water phases contained a sugar capable of forming a glassy phase, while the oil was crystallizable upon freezing. Freeze drying the double emulsion allowed removing the oil and water and replacing them with air without losing the three-dimensional (3D) structure of the original emulsion owing to the sugar glassy phase. Reconstitution of the freeze-dried double emulsion in water yielded a dispersion of antibubbles, i.e., micrometric bubbles containing aqueous droplets, with the interfaces of the antibubbles being stabilized by a layer of adsorbed polymeric nanoparticles. Remarkably, it was possible to achieve controlled release of a flourescent probe (calcein) from the antibubbles through heating to 37 °C leading to bursting of the antibubbles

Pickering Emulsions and Antibubbles Stabilized by PLA/PLGA Nanoparticles

Micrometer-sized double emulsions and antibubbles were produced and stabilized via the Pickering mechanism by colloidal interfacial layers of polymeric nanoparticles (NPs). Two types of nanoparticles, consisting either of polylactic acid (PLA) or polylactic-co-glycolic acid (PLGA), were synthesized by the antisolvent technique without requiring any surfactant. PLA nanoparticles were able to stabilize water-in-oil (W/O) emulsions only after tuning the hydrophobicity by means of a thermal treatment. A water-in-oil-in-water (W/O/W) emulsion was realized by emulsifying the previous W/O emulsion in a continuous water phase containing hydrophilic PLGA nanoparticles. Both inner and outer water phases contained a sugar capable of forming a glassy phase, while the oil was crystallizable upon freezing. Freeze drying the double emulsion allowed removing the oil and water and replacing them with air without losing the three-dimensional (3D) structure of the original emulsion owing to the sugar glassy phase. Reconstitution of the freeze-dried double emulsion in water yielded a dispersion of antibubbles, i.e., micrometric bubbles containing aqueous droplets, with the interfaces of the antibubbles being stabilized by a layer of adsorbed polymeric nanoparticles. Remarkably, it was possible to achieve controlled release of a flourescent probe (calcein) from the antibubbles through heating to 37 °C leading to bursting of the antibubbles

Polymer Molecular Architecture As a Tool for Controlling the Rheological Properties of Aqueous Polyacrylamide Solutions for Enhanced Oil Recovery

The controlled synthesis of high molecular weight branched polyacrylamide (PAM) has been accomplished by using atomic transfer radical polymerization (ATRP) of acrylamide (AM) in water at room temperature. Halogen-functionalized aliphatic polyketones acted as macroinitiators in the polymerization. The obtained branched polymers were used in water solutions to study the effect of the molecular architecture on the rheological properties. For comparison purposes, linear PAM was synthesized by using the same procedure. The intrinsic viscosities and light scattering data suggest that the 13- and 17-arm PAMs are more extended in solution compared to the linear, 4-arm, and 8-arm analogues, at equal total molecular weight. The comparison of linear and 4-, 8-, 12-, 13-, and 17-arm PAM in semidilute solutions demonstrated that the 13- and 17-arm PAM have the highest solution viscosity at equal molecular weight. Depending on the PAM molecular weight and concentration, a significant (as much as 5-fold) increase in solution viscosity (at a shear rate of 10 s^–1) is observed. The elastic response of aqueous solutions containing the polymers critically depended on the molecular architecture. Both the 4- and 8-arm polymers displayed a larger phase angle value compared to the linear analogue. The 13- and 17-arm PAMs displayed a lower phase angle than the linear one. Ultimately, the rheological properties are dependent on the number of arms present. The combination of a higher hydrodynamic volume and higher entanglement density leads to an improved thickening efficiency (for <i>N</i> ≥ 13, <i>N</i> being the average number of arms). The improved thickening efficiency of the branched (<i>N</i> ≥ 13) PAMs makes these polymers highly interesting for application in Enhanced Oil Recovery and drag reduction

Kinetic Study on the Sulfuric Acid-Catalyzed Conversion of d‑Galactose to Levulinic Acid in Water

Levulinic acid is an interesting building block for biofuel (additives) and biobased chemicals. It is accessible by an acid-catalyzed reaction of a wide variety of carbohydrates. We here report a kinetic study on the conversion of d-galactose to levulinic acid in aqueous solutions with sulfuric acid as the catalyst. The experiments were carried out in a broad range of temperatures (140–200 °C), initial concentrations of galactose (0.055–1.110 M), and concentrations of sulfuric acid (0.05–1 M). The experimental data were modeled using a power-law approach, and good agreement between the experimental data and the model was obtained. The maximum yield of levulinic acid (54 mol %) was achieved at 130–140 °C, low initial galactose concentrations (0.055 M), and high acid concentrations (1 M). With the kinetic information available, the most suitable reactor configuration was determined, and it is predicted that a continuously stirred-tank reactor is preferred over a plug-flow reactor. The findings presented here may also be applicable to the kinetic modeling of levulinic acid synthesis from more complex biomass sources such as lignocellulosic (woody) and aquatic (e.g., seaweed) biomass

Efficient Conversions of Macroalgae-Derived Anhydrosugars to 5‑Hydroxymethylfurfural and Levulinic Acid: The Remarkable Case of 3,6-Anhydro‑d‑galactose

Macroalgae or seaweed is considered a renewable and sustainable resource to produce biobased fuels, polymers, and chemicals due to its high content of polysaccharides. Various studies have reported the obtained 5-hydroxymethylfurfural (HMF) and levulinic acid (LA) from seaweeds. However, the source of the saccharides that is responsible for HMF formation, accurate yield data (often only HMF concentrations are given instead of yields on feed), and the reaction pathways (including byproducts) is not well understood. We here report a kinetic study on the conversion of 3,6-anhydro-d-galactose (D-AHG), one of the main building blocks of the polysaccharides in seaweed, to HMF and LA in water using sulfuric acid as a catalyst with the aim to rationalize and optimize the production of HMF and LA from seaweeds. The experiments were carried out in batch at temperatures between 160 and 200 °C using various initial concentrations of D-AHG (0.006–0.06 M) and sulfuric acid (0.0025–0.05 M) as the catalyst. The highest experimental yield of HMF within this range of experimental conditions was remarkably high (61 mol %) and obtained at 160 °C, with a low initial D-AHG concentration (0.006 M) and a low acid concentration (0.0025 M). These findings imply that D-AHG is a very good precursor for the HMF synthesis. Additional experiments outside the experimental window gave an even higher HMF yield of 67 mol %. The highest LA yields were 51 mol % [160 °C, low initial D-AHG concentration (0.006 M), and high acid concentration (0.05 M)]. The experimental data were modeled using a power law approach, and the kinetic model was used to determine reactor configurations giving the maximum yield of HMF and LA. The result showed that a plug flow reactor is favorable to achieve the highest yield of HMF, whereas a continuously ideally stirred tank reactor is the preferable reactor configuration to obtain the highest yield of LA

Electroactive Self-Healing Shape Memory Polymer Composites Based on Diels–Alder Chemistry

Both shape memory and self-healing polymers have received significant attention from the materials science community. The former, for their application as actuators, self-deployable structures, and medical devices; and the latter, for extending the lifetime of polymeric products. Both effects can be stimulated by heat, which makes resistive heating a practical approach to trigger these effects. Here we show a conductive polyketone polymer and carbon nanotube composite with cross-links based on the thermo-reversible furan/maleimide Diels–Alder chemistry. This approach resulted in products with efficient electroactive shape memory effect, shape reprogrammability, and self-healing. They exhibit electroactive shape memory behavior with recovery ratios of about 0.9; requiring less than a minute for shape recovery; electroactive self-healing behavior able to repair microcracks and almost fully recover their mechanical properties; requiring a voltage in the order of tens of volts for both shape memory and self-healing effects. To the best of our knowledge, this is the first report of electroactive self-healing shape memory polymer composites that use covalent reversible Diels–Alder linkages, which yield robust solvent-resistant polymer networks without jeopardizing their reprocessability. These responsive polymers may be ideal for soft robotics and actuators. They are also a step toward sustainable materials by allowing an increased lifetime of use and reprocessability