Rheology and viscosity scaling of the polyelectrolyte xanthan gum

The viscosity as a function of concentration for xanthan gum in both salt‐free solution and in 50 mM NaCl is measured and compared with a scaling theory for polyelectrolytes. In general, the zero shear rate viscosity and the degree of shear thinning increase with polymer concentration. In addition, shear thinning was observed in the dilute regime in both solvents. In salt‐free solution, four concentration regimes of viscosity scaling and three associated critical concentrations were observed (c* ≈ 70 ppm, c_e ≈ 400 ppm, and c_D ≈ 2000 ppm). In salt solution, only three concentration regimes and two critical concentrations were observed (c* ≈ 200 ppm and c_e ≈ 800 ppm). In the presence of salt, the polymer chain structure collapses and occupies much less space resulting in higher values of the critical concentrations. The observed viscosity‐concentration scaling is in very good agreement with theory in the semidilute unentangled and semidilute entangled regimes in both salt‐free and 50 mM NaCl solution. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Hydrophobically modified poly(sodium 2‐acrylamido‐2‐methylpropanesulfonate): synthesis and viscosity of aqueous solution

BACKGROUND: Hydrophobically modified polyelectrolytes are widely used polymers due to their good water solubility, stretched configuration in water and strong hydrophobic association. The study reported here aimed at researching the double action of hydrophobic association and electrostatic effect of novel hydrophobically modified polyelectrolytes in solution. RESULTS: A series of novel hydrophobically modified polyelectrolytes were synthesized by micellar copolymerization with various feed ratios of sodium 2‐acrylamido‐2‐methylpropanesulfonate, N‐n‐dodecylamine and sodium dodecylsulfonate. Their structure was characterized using Fourier transform infrared spectroscopy, nuclear magnetic resonance and gel permeation chromatography, and the viscosities of their aqueous and salt solutions were studied. CONCLUSION: The results show that the addition of the hydrophobic comonomer results in a decrease in molecular weight (M_w). The smaller the initial number of hydrophobes in one micelle, the higher is M_w of the resulting copolymer. The viscosity of PAD‐1.73 polyelectrolyte is less sensitive to salt than those of the others. According to the zero shear viscosity and corresponding concentration, the critical cluster‐forming concentration, critical overlap concentration and critical entanglement concentration of these polymer solutions were determined. Moreover, in the dilute regime the viscosity decreases with increasing salinity, while in the semi‐dilute regime the viscosity decreases first and then increases. It is suggested that in dilute and semi‐dilute regimes, hydrophobic intramolecular association and intermolecular association dominate, respectively. Copyright © 2009 Society of Chemical Industry     

Altering the viscosity of cationically modified cellulose polymers by the addition of salt

The concentration dependence of viscosity is examined for four cationically modified cellulose polymers (UCARE? JR400, UCARE? JR30M, UCARE? LR400, and UCARE? LR30M) in both salt‐free and 50 mM NaCl solution. Similarities in the four polymer systems include: Newtonian viscosity in the dilute regime, shear thinning at higher concentrations, four concentration regimes in salt‐free solution, and three concentration regimes in salt solution. The zero shear rate viscosity and the degree of shear thinning increase with increasing polymer concentration in both salt and salt‐free solutions. While the addition of salt to the lower molecular weight polymers JR400 and LR400 resulted in small changes in viscosity across all concentrations, JR30M and LR30M exhibited significant decreases (up to 81%) and increases (up to 57%) in viscosity upon the addition of salt in the semidilute and entangled regimes, respectively. This viscosity increase in the entangled regime (when comparing salt‐free and 50 mM NaCl solutions) is reported for the first time in cationically modified cellulose polymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41616.     

Rheological studies of hyaluronan solutions based on the scaling law and constitutive models

We have investigated the scaling relationship between rheological behavior and concentration for both salt-free and saline solutions of hyaluronan (HA), and adopted three viscoelastic constitutive models to predict the linear/non-linear viscoelastic behavior of these aqueous solutions of HA with different molecular weights at different concentrations up to 20 mg/ml. A series of concentration equations are obtained to describe the influence of HA concentration on solution viscosity. Corresponding to dilute and semi-dilute concentration region, salt-free HA solutions have scaling relationship between specific viscosity and HA concentration as η_sp ∼ c^1.0 and η_sp ∼ c^3.5, respectively, while for 0.15 M NaCl HA solutions, the scaling exponents are 1.5 and 4.2, respectively. Simulation results indicate that these constitutive models have good applicability to describe quantitatively the rheological properties of HA entangled solutions under either dynamic or steady shear flow. In addition, the plateau modulus scaling of HA solutions can be well described by the concentration-dependent length scale.     

Rheological behaviour of polystyrene latex near the maximum packing fraction of particles

Additional developments in the comprehension of the rheological behaviour of polymer latices, especially near the high critical concentration ?_c, are presented for two polystyrene latices of average particle diameters close to 200 nm with different electrostatic properties. Not surprisingly, there is a rapid transition in the rheological characteristics over a narrow range of polymer volume fractions as the concentration of the disperse phase increases. By examining twelve different polymer volume fractions a unique value of the critical volume concentration, ?_c, was found for each latex. At this point, the steady shear viscosity, dynamic modulus, and dynamic shear viscosity change dramatically. Furthermore, these critical concentrations are well confirmed by the percolation theory for the dynamic zero shear viscosity as a function of volume fraction. The Cox-Merz rule is not obeyed by these dispersions at the concentrations greater than ?_c. By using a controlled strain Couette rheometer with a gap of 1.2 mm, shear thickening limits were also observed for both latices. The concentration dependence of the onset shear rate for shear thickening changes near ?_c for each of the two latices.     

Equation of state for polymer solution

The flow pattern through a cloud of polymer segments is obviously different from the flow pattern around a solid object. It can be shown theoretically, however, that the partial viscosity due to the cloud can take the same value as for a solid sphere with the radius of gyration of the cloud as its radius. The specific viscosity of polymer solution has been derived as 2.5(c/c_I), with c_I being the internal concentration associated with a polymer molecule. The internal concentration is the ratio of mass over the volume of gyration of segments in a polymer chain. A radius of gyration exists for any type of polymers, flexible or rigid, exhibiting different kinds of dependence on the molecular weight. From the expression of the specific viscosity, the intrinsic viscosity is shown to be equal to 2.5/c^∗, c^∗ being the (minimum) internal concentration for the state of maximum conformational entropy. The equation for the specific viscosity, thus obtained, is expanded into a polynomial in c[η]. This formula is shown to agree with data for several kinds of polymers, with flexible, semi-rigid and rigid.The quantity 1/c_I can be interpreted as an expression for the chain stiffness. In polyelectrolytes, coulombic repulsive potentials affect the chain stiffness. The dependence of c_I on the effective population of polyions in the polyelectrolyte molecule is discussed.An equation of state for the polymer solution is formulated that included the internal concentration. The virial coefficients emerge as a result of c_I not always being equal to c^∗, and they are molecular weight dependent.     

Solvents effect on the physical properties of semi-dilute poly(N-isopropyl acryl amide) solutions

The physical properties of 5 wt% poly(NIPAM) (M_v=3.22×10⁵) semi-dilute solutions in H₂O, D₂O, and THF (tetrahydrofuran) solvents were studied using dynamic light scattering (DLS) and dynamic shear viscosity (DSV) measurements. The DLS data showed that there were poly(NIPAM) slow mode inter-polymer chains associations in H₂O and D₂O solvents. However, no DLS slow mode was observed in poly(NIPAM)/THF solutions. The DSV data showed that there are shear thickening behavior in these three poly(NIPAM) solutions, resulting in a maximum shear viscosity η_peak in the viscosity η′(ω) versus shear frequency ω curve. The slow mode hydrodynamic radius 〈R_hs〉 of DLS measurements and the zero shear rate viscosity η₀ and maximum viscosity η_peak data of DSV measurements from poly(NIPAM)/H₂O and poly(NIPAM)/D₂O solutions show two critical transition temperatures with T_cr1=30-32 °C and T_cr2=32-34 °C. Poly(NIPASM)/D₂O has higher T_cr1 and T_cr2 than poly(NIPASM)/H₂O. However, no transition temperatures of poly(NIPAM)/THF solution were observed. The different temperature dependencies of these three solutions were attributed to the ‘solubility’ and ‘hydrogen bonding’ effects between poly(NIPAM) with H₂O, D₂O, and THF solvents. Without considering the polymer-solvent hydrogen bonding, the solubility of poly(NIPAM) in solvents decreases in the following sequence: THF>H₂O>D₂O and the degree of polymer-solvent hydrogen bonding increases in the following sequence: THF<H₂O<D₂O. The effects of the degree of ‘hydrogen bonding’ and the ‘solubility’ of polymer in solvents on the physical properties of poly(NIPAM) solutions are discussed.     

Cyanine dye polyelectrolytes for organic bilayer solar cells

Polyelectrolytes composed of an anionic sulfoethyl methacrylate/methacrylate backbone and cationic cyanine dyes counter ions are synthesized. The effective reaction sequence is confirmed by NMR spectroscopy and consists of a thermal radical copolymerization to obtain the polymer backbone (M_n ∼ 40 kg mol⁻¹), followed by deprotonation of the sulfoethyl group and a salt metathesis reaction with elimination of silver halide to incorporate the dye. With increasing cyanine content (20–50% of polymer repeating units) polyelectrolytes become insoluble in apolar solvents. This allows the fabrication of simple solution-processed bilayer organic solar cells, where an electron acceptor fullerene layer is coated from the orthogonal solvent chlorobenzene onto an underlying polyelectrolyte electron donor layer. The optimization of solar cells is described, and photo-CELIV measurements are used to identify the low hole mobility in the polyelectrolyte layer as the main reason that currently limits solar cell performance to ∼0.9%.     

Electrospinning of linear homopolymers of poly(methyl methacrylate): exploring relationships between fiber formation, viscosity, molecular weight and concentration in a good solvent

A series of seven linear homopolymers of poly(methylmethacrylate) ranging from 12,470 to 365,700 g/mol M_w, were utilized to further explore scaling relationships between viscosity and concentration in a good solvent at 25 °C and to investigate the impact of these relationships on fiber formation during electrospinning. For each of the polymers investigated, chain dimensions (hydrodynamic radius and radius of gyration) were measured by dynamic light scattering to determine the critical chain overlap concentration, c^*. The experimentally determined c^*, was found to be in good agreement with the theoretically determined value that was calculated by the criteria c^*∼1/[η], where the intrinsic viscosity was estimated from the Mark-Houwink parameters, K and a (at 25 °C in dimethyl formamide) obtained from the literature. The plot of the zero shear viscosity vs. c/c^* distinctly separated into different solution regimes, viz. dilute (c/c^*<1), semidilute unentangled (1<c/c^*<3) and semidilute entangled (c/c^*>3). The crossover between semidilute unentangled and semidilute entangled regimes in the present investigation occurred at c/c^*∼3, which, therefore, marked the onset of the critical chain entanglement concentration, c_e, according to the procedure utilized by Colby and co-workers [Colby RH, Rubinstein M, Daoud M. J de Phys II 1994;4(8):1299-310. [52]]. Electrospinning of all solutions was carried out at identical conditions to ascertain the effects of solution concentration, molecular weight, molecular weight distribution and viscosity on fiber formation and morphological features of the electrospun material. Only polymer droplets were observed to form from electrospinning of solutions in the dilute concentration regime due to insufficient chain overlap. As the concentration was increased, droplets and beaded fibers were observed in the semidilute unentangled regime; and beaded as well as uniform fibers were observed in the semidilute entangled regime. Uniform fiber formation was observed at c/c^*∼6 for all the narrow MWD polymers (M_w of 12,470-205,800 g/mol) but for the relatively broad MWD polymers (M_w of 34,070 and 95,800 g/mol), uniform fibers were not formed until higher concentrations, c/c^*∼10, were utilized. Dependence of fiber diameter on concentration and viscosity was also determined, viz. fiber dia∼(c/c^*)^3.1 and respectively. These scaling relationships were in general agreement with that observed by Mckee et al. [McKee MG, Wilkes GL, Colby RH, Long TE. Macromolecules 2004;37(5):1760-67. [33]].     

Hybrid nanocomposites of semiconductor nanoparticles and conjugated polyelectrolytes and their application as fluorescence biosensors

Weakly emissive silicon nanoparticles with an average diameter of about 5 nm are prepared via pulsed laser ablation of silicon wafers in water. Electrostatic assembly of water-soluble conjugated polyelectrolytes on the surface of the silicon nanoparticles steadily enhances the photoluminescence of these nanocomposites, indicating the possibility of energy transfer between the semiconductor nanoparticles and the conjugated polymer, or silicon nanoparticle-induced elimination of chain aggregates of the conjugated polyelectrolyte. Fluorescence emission of the hybrid silicon-conjugated polymer nanocomposites is steeply quenched by cytochrome c, and the minimum detection concentration for the redox-active protein is found to be 50 nM. The sensitization is realized by ultrafast photoinduced electron transfer between the electron-deficient protein and the conjugated polyelectrolyte binding on the silicon nanoparticle surfaces. The results offer guidelines to explore novel sensors for detecting nanoparticles, and also help develop high-efficiency sensory materials based on electrostatic complexes of conjugated polyelectrolytes and inorganic semiconductor nanoparticles.     

Scaling of activation energy for macroscopic flow in poly(ethylene glycol) solutions: Entangled – Non-entangled crossover

We postulate an empirical scaling equation, which accurately describes flow of polymer solutions, complimenting the paradigm of length-scale-dependent viscosity. We investigated poly(ethylene glycol) aqueous solutions and observed an exponential dependence of viscosity on the hydrodynamic radius of a single coil R_h divided by the correlation length ξ. Properties of the system changed abruptly with the onset of chain entanglement at concentration corresponding to ξ = R_h. We propose a single equation valid for all the investigated systems, analyze the physical meaning of parameters appearing therein and discuss the impact of chain entanglement. Viscous flow is treated as an activated process, following the Eyring rate theory. We show that the difference of activation energy for flow between pure solvent and polymer solution, ΔE_a, is a function of concentration, whose derivative has a discontinuity at the crossover concentration. For dilute PEG solutions ΔE_a takes values of up to several kJ/mol and is proportional to the intrinsic viscosity. We successfully apply the scaling approach to the diffusive motion of a protein (aldolase) in solutions of 25 kg/mol PEO (concentrations of 2–20%), investigated by fluorescence correlation spectroscopy (FCS). A significant difference in the influence of crowding on translational and rotational motion of the protein is revealed.     

Viscosity properties of homogeneous polyelectrolyte complex solutions from sodium carboxymethyl cellulose and poly(acrylamide‐co‐dimethyldiallylammonium chloride)

The viscosity properties of homogeneous polyelectrolyte complex solutions of sodium carboxymethyl cellulose (CMC) and poly(acrylamide‐co‐dimethyldiallylammonium chloride) have been investigated by means of a rotation viscometer at different complexation ratios, shear rates and temperatures. Compared with aqueous solutions of the component polyelectrolytes, such complex solutions can afford substantially increased viscosities at the complexation ratios examined, together with enhanced shear‐thinning rheology and temperature stability. According to this study, it is possible to improve the viscosity properties of water‐soluble polymers by homogeneous interpolyelectrolyte complexation in aqueous solutions. © 2000 Society of Chemical Industry     

Dipolar polymeric compounds and their properties in the aqueous medium

Reactions between poly(4-vinylpyridine) and acrylic acid as well as poly(vinylimidazole) and the same acid led to polymers containing carboxybetaine repeating units with a percentage higher than 90%. Chemical structures and compositions of chemically modified polymers were established from their ¹H NMR and IR spectra. The solution properties of the two poly(carboxybetaines) were analyzed by potentiometric titrations and viscometric measurements. Deionized water as well as CaCl₂ and NaCl aqueous solutions of different concentrations were used as solvents. From potentiometric titrations with 0.5 M HCl, the apparent pK_a values were determined using Henderson–Hasselbach equation. These values are strongly depended of the solvent nature. Thus, both poly(carboxybetaines) have the lowest pK_a values when deionized water was used as solvent. Therefore, the lowest binding ability of the H⁺ by COO⁻ groups occurs in this solvent.The viscometric measurements revealed that reduced viscosity values are non-responsive towards the polymer solution concentrations irrespective of the used solvent (i.e., deionized water or NaCl and CaCl₂ aqueous solutions). Therefore, the behaviour of these carboxybetaine macromolecules in the above-mentioned solvents is that of hung up hard spheres. Consequently, the intrinsic viscosity values were calculated according to the Einstein–Simha equation applicable for such systems. The [η] versus salt solution concentration plots show a decreasing part in the concentration range from 0 to 0.05 M that is followed by a slow [η] increasing.In 0.5 M HCl both poly(carboxybetaines) exhibit the viscometric polyelectrolyte behaviours because of their shift to the corresponding cationic polyelectrolytes.     

Dilute solution properties of anionic poly(potassium-2-sulphopropylacrylate)

The dilute solution properties of an anionic polyelectrolyte, poly(potassium-2-sulphopropylacrylate) (poly(SPA)) are studied by measurements of intrinsic viscosity, degree of binding, ionic strength and critical micelle concentration. The intrinsic viscosity of this polyelectrolyte is related to the type and concentration of the salt added. The intrinsic viscosity behaviour of an anionic polyelectrolyte resulting from the electrostatic repulsive force of the polymer chain is in contrast to that of a polyampholyte. The polyelectrolyte in high concentration of NaCl has a low degree of binding, indicating that the proton ion (H⁺) is relatively difficult to bind to the sulphonate group (SO⁻₃) at the polymer end. An increase in ionic strength causes the pK_a to decrease at the half-neutralization point. The monomer solutions exhibit a plot typical of those observed for detergents, with a break in the curve occurring at the critical micelle concentration. For the polymer solutions, no break in the equivalent conductance curve was found for the concentrations studied.     

Physico-chemical concept of drag reduction nature in dilute polymer solutions (the Toms effect)

The physicochemical concept of turbulent drag reduction (the Toms effect) integrates physicochemical characteristics of polymer solutions with hydrodynamic and rheological flow parameters into a generalized equation, where the increment in volumetric flow rate Q_P is a function of the external shear stress τ_w, temperature, volume of macromolecular coils with immobilized solvent V_c and a function of their volume fraction Ψ = C · [η]/(1 + C · [η]). The Q_P depends on the coil intrinsic elasticity [G] = kT/V_c as well. This model allows one: (1) to describe the Toms effect in terms of useful elastic work spent by macromolecular coils with immobilized solvent to overcome the frictional forces (i.e. the forces of intermolecular interactions), (2) to forecast the initial conditions of the Toms effect (τ_* ≈ (RT)/(M · [η])) and (3) to explain the unusual temperature dependence of the polymer solutions flow.     

Shear thickening behavior of dilute poly(diallyl dimethyl ammonium chloride) aqueous solutions

Using dynamic light scattering (DLS) and capillary dynamic viscoelasticity (DVE) analyzer, we investigated dilute (0.5 mg/ml) poly(diallyl dimethyl ammonium chloride) (PDADMAC) aqueous solution properties for three different molecular weights of PDADMACs mixed with various concentrations of NaCl. The dependence of PDADMAC molecular chain conformations in aqueous solutions on polymer molecular weight and NaCl concentration were studied. By analyzing dynamic shear viscosity η′(ω), viscoelastic relaxation times t_r, and shear rate at tube wall ?_a(ω) of PDADMAC aqueous solutions in oscillatory flows, we proposed that polymer chain conformations varied with increasing shear frequency ω via the following steps: intra-polymer associations, dissociation of intra-polymer associations, stretching of polymer chains, inter-polymer aggregations, and dissociations of inter-polymer aggregations. The intra-polymer associations lowered the n′ exponent of storage modulus G′(ω) (G′(ω) ∼ ω^n′) with n′ < 2, and the polymer chain stretching and inter-polymer aggregations caused shear thickening (i.e. upturn of η′(ω)) of PDADMAC aqueous solutions. The behaviors of the lowering of n′ exponent with n′ < 2 and the shear thickening were favored by increasing ionic strength of solutions. By comparing η′(ω) data with DLS hydrodynamic radii (R_h) data, we also confirmed the possibility of inter-polymer aggregations in dilute solutions when polymer chains were stretched in oscillatory flows.     

Diffusion of rigid rodlike polymer in isotropic solutions studied by dissipative particle dynamics simulation

Dissipative particle dynamics (DPD) was employed to simulate the diffusion of rigid rodlike polymers in isotropic solutions. In a dilute solution range, the simulated diffusion behavior is in good agreement with that as described by the Kirkwood theory. In a semi-dilute range, the simulation shows that the DPD model adopting soft repulsive interactions can effectively reproduce the entanglement effect on both rotational and translational diffusions. The rotational diffusion coefficient D_r obeys the asymptotic scaling law D_r ∼ (νL³)⁻² (ν is the number of polymers per volume and L is the polymer length) for the large νL³, which corresponds to formation of a completely enclosed tube in the Doi-Edwards theory. The parallel translational diffusion coefficient D_‖ decreases with ν increase, which can be attributed to the friction effect of surrounding medium. The perpendicular translational diffusion coefficient D_⊥ decays more drastically with ν increase, which is caused by the topological constraint.     

Characterization of viscoelastic properties of polyacrylamide/Cr(III) hydrogels

Summary The viscoelastic properties of polyacrylamide/Cr(III) hydrogels were characterized with the help of oscillatory shear rheometer. The serrated-plate geometry rather than the cone-plate geometry was used in order to avoid the slip effect. The dynamic storage modulus (G') increased with increasing polyacrylamide and/or Cr(III) concentrations. The mean molecular weight of the chains adjoining adjacent crosslinks (M_c), calculated according to the elastic rubber theory, exhibited the same order of the primary polymer. G' decreased with increasing monovalent salt concentration, owing to the polyelectrolyte effect.     

Rheological properties of a hydrophobically modified anionic polymer: Effect of varying salinity and amount of hydrophobic moieties

Hydrophobically modified polyelectrolytes have been suggested as an alternative to the more commonly used polyelectrolytes in enhanced oil recovery (EOR) applications involving polymers. Compared to regular polyelectrolytes, the hydrophobically modified polyelectrolytes are known to be more stable at high salinities. In this study, we have investigated the influence of brine salinity and ionic composition for a series of six hydrophobically modified polyelectrolytes with the same polymer backbone, but with an increasing average number of hydrophobic groups per polymer molecule. Polymer characterization has been performed using a combination of steady‐state shear viscosity and dynamic oscillatory measurements. Hydrophobic interactions leading to a change in rheological properties was only observed above a threshold value for the concentration of hydrophobe. At the threshold value, salt‐induced hydrophobic interactions were observed. For higher concentrations of hydrophobe, high salinity solutions showed one order of magnitude increase in viscosity compared to the polymer without hydrophobic groups. This could partly be explained by an increase in elasticity. These findings have important implications for polymer selection for EOR. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43520.     

Synthesis and electrostatic assembly of an optically active derivative of poly(ethylene-alt-maleic anhydride) with l-phenylalanine as a chiral material

The layer-by-layer (LbL) assembly of polyelectrolytes is an excellent method for the fabrication of functional ultra-thin multilayers. The functional properties of the film depend on the nature of the polyelectrolyte. Thus, to develop new applications for LbL multilayer films, it is first necessary to synthesize new functional polyelectrolytes. We have prepared a novel, optically active polyelectrolyte, an l-phenylalanine derivative of poly(ethylene-alt-maleic anhydride) (PEMA-l-Phe), via ring-opening of the succinic anhydride unit. We have characterized this polyelectrolyte by FTIR, UV–Vis spectroscopy, ¹H NMR, and polarimetric analysis. The specific rotatory power, [α]_D, of the chiral polymer was ?101.3°, greater than that of l-phenylalanine (?35.1°). We fabricated an ultra-thin film of (PEMA-l-Phe)/poly(allylamine hydrochloride) (PAH) with the electrostatic LbL self-assembly method. The assembly of this ultra-thin film was monitored with a UV–Vis spectrophotometer. The results indicate that the absorbance of the multilayer at 210 nm grows exponentially with the number of bilayers, and that the mass of each bilayer is 1.263 times that of the previous bilayer. This multilayer has potential applications in chiral identification and separation.