Polymers for enhanced oil recovery: A paradigm for structure–property relationship in aqueous solution

When aqueous solutions of polycations and polyanions are mixed, polyelectrolyte complexes form. These are usually insoluble in water, so that they separate out as a new concentrated polymer phase, called a complex coacervate. The behavior of these complexes is reviewed, with emphasis on new measurements that shed light on their structural and mechanical properties, such as cohesive energy, interfacial tension, and viscoelasticity. It turns out that stoichiometric complexes can be considered in many respects as pseudo-neutral, weakly hydrophobic polymers, which are insoluble in water, but become progressively more soluble as salt is added. In fact, the solubility-enhancing effect of salt is quite analogous to that of temperature for polymers in apolar solvents. Since two-phase systems can be prepared in colloidal form, we also discuss several kinds of colloids or 'microphases' that can arise due to polyelectrolyte complexation, such as thin films, 'zipper' brushes, micelles, and micellar networks. A characteristic feature of these charge-driven two-phase systems is that two polymeric ingredients are needed, but that some deviation from strict stoichiometry is tolerated. This turns out to nicely explain how and when the layer-by-layer method works, how a 'leverage rule' applies to the density of the 'zipper brush', and why soluble complexes or micelles appear in a certain window of composition. As variations on the theme, we discuss micelles with metal ions in the core, due to incorporation of supramolecular coordination polyelectrolytes, and micellar networks, which form a new kind of physical gels with unusual properties.

Polyelectrolyte complexes: Bulk phases and colloidal systems

Water soluble polymers with pendant hydrophobic substituents associate in water to form extended structures. Solutions of the polymers have important applications in technologies ranging from paints and paper coatings (as rheology modifiers) to DNA sequencing (where the network structure serves as a sieving medium). Recent experiments are beginning to reveal the nature of the structures formed and their response to shear. Many facets of the behavior of these polymers are under active investigation.

http://mitran-lab.amath.unc.edu:8082/subversion/Papers/2011/VE_Entrain_JCP_Spec_Issue_MMS/biblio/NetworkModels/WennikYekta_AssociativePolymersAqueousSolution_1997.pdf

Associative polymers in aqueous solution

In this review, I present an idiosyncratic view of the current state of shear banding in complex fluids. Particular attention is paid to some of the outstanding issues and questions facing the field, including the applicability of models that have “traditionally” been used to model experiments; future directions and challenges for experimentalists; and some of the issues surrounding vorticity banding, which has been discussed theoretically and whose experiments are fewer in number yet, in many ways, more varied in character.

Perspectives on shear banding in complex fluids

In conventional polymer materials, mechanical performance is traditionally engineered via material structure, using motifs such as polymer molecular weight, polymer branching, or block copolymer design. Here, by means of a model system of 4-arm poly(ethylene glycol) hydrogels crosslinked with multiple, kinetically distinct dynamic metal-ligand coordinate complexes, we show that polymer materials with decoupled spatial structure and mechanical performance can be designed. By tuning the relative concentration of two types of metal-ligand crosslinks, we demonstrate control over the material's mechanical hierarchy of energy-dissipating modes under dynamic mechanical loading, and therefore the ability to engineer a priori the viscoelastic properties of these materials by controlling the types of crosslinks rather than by modifying the polymer itself. This strategy to decouple material mechanics from structure is general and may inform the design of soft materials for use in complex mechanical environments. Three examples that demonstrate this are provided.

/pdf/control-of-hierarchical-polymer-mechanics-with-bioinspired-xlvsyzpr5y.pdf

Control of hierarchical polymer mechanics with bioinspired metal-coordination dynamics

The properties of aqueous solutions of model HEUR associative thickeners under dynamic and steady shear have been studied as a function of concentration, molecular weight, temperature, and hydrophobic end‐cap length. It is shown that solutions of AT behave as near perfect Maxwell fluids inasmuch that Cole–Cole plots of the dynamic moduli are almost exactly semi‐circular. An Arrhenius law temperature dependence of the static viscosity and relaxation time is also observed, providing confirmation of a single relaxation process. In certain other respects, AT solutions show more complex behavior, e.g., the Cox–Merz rule is not obeyed, with the steady shear viscosity showing a weaker dependence on shear rate than does the complex viscosity upon frequency. Furthermore, weak shear thickening is seen to precede shear thinning in steady shear. The above results are consistent with the predictions of a transient network theory presented recently by Tanaka and Edwards and Jenkins (generalized Green–Tobolsky theory). ...

https://sor.scitation.org/doi/pdf/10.1122/1.550391

The rheology of solutions of associating polymers: Comparison of experimental behavior with transient network theory

Influence of surfactants on the rheology of associating polymers in solution

Network formation and its consequences for the physical behaviour of associating polymers in solution

The phase behavior of mixtures of a hydrophobically modified polymer capable of forming associations and an unmodified polymer of the same chemical composition has been investigated. The associative thickener (AT) consists of poly(ethylene glycol) (PEG) end-capped at both ends with hydrophobic alkane groups. It is found that mixtures of the AT solution and the unmodified PEG phase separate into two distinct solutions, provided AT molar fractions are <0.65. This is despite the fact that the overall polymer concentration throughout both phases remains the same. However, the viscosities of the two phases were found to be very different

Thermodynamics of phase separation in mixtures of associating polymers and homopolymers in solution

The present study focuses on the use of copolymer nanoparticles as a dispersant for a model pigment (silica). Reversible addition–fragmentation chain transfer (RAFT) alcoholic dispersion polymerization was used to synthesize sterically stabilized diblock copolymer nanoparticles. The steric stabilizer block was poly(2-(dimethylamino)ethyl methacrylate) (PDMA) and the core-forming block was poly(benzyl methacrylate) (PBzMA). The mean degrees of polymerization for the PDMA and PBzMA blocks were 71 and 100, respectively. Transmission electron microscopy (TEM) studies confirmed a near-monodisperse spherical morphology, while dynamic light scattering (DLS) studies indicated an intensity-average diameter of 30 nm. Small-angle X-ray scattering (SAXS) reported a volume-average diameter of 29 ± 0.5 nm and a mean aggregation number of 154. Aqueous electrophoresis measurements confirmed that these PDMA71–PBzMA100 nanoparticles acquired cationic character when transferred from ethanol to water as a result of protonati...

https://pubs.acs.org/doi/pdf/10.1021/acs.langmuir.6b04541

Adsorption of Small Cationic Nanoparticles onto Large Anionic Particles from Aqueous Solution: A Model System for Understanding Pigment Dispersion and the Problem of Effective Particle Density

Tom Annable

Papers

The rheology of solutions of associating polymers: Comparison of experimental behavior with transient network theory

Influence of surfactants on the rheology of associating polymers in solution

Network formation and its consequences for the physical behaviour of associating polymers in solution

Thermodynamics of phase separation in mixtures of associating polymers and homopolymers in solution

Adsorption of Small Cationic Nanoparticles onto Large Anionic Particles from Aqueous Solution: A Model System for Understanding Pigment Dispersion and the Problem of Effective Particle Density