Rheological properties of carboxymethyl cellulose (CMC) solutions

In this study, we investigated the way of predicting two critical concentrations of sodium carboxymethyl cellulose (CMC) solutions using simple experimental procedures with a rotational rheometer. It was found that, above a critical shear rate, all CMC solutions (0.2 to 7 wt.%) exhibit shear-thinning behavior and the flow curves could be described by the Cross model. A first critical CMC concentration c*, transition to semidilute network solution, was determined using the following methods (1) study of the flow curve shapes, (2) Cross model parameters, (3) plot of the specific viscosity vs the overlap parameter, and (4) empirical structure–properties relationships. Furthermore, both creep and frequency-sweep measurements showed that the solutions behaved as viscoelastic materials above a second critical CMC concentration c** (transition to concentrated solution). The characterization of CMC solutions was completed with a time-dependent viscosity study that showed that the CMC solutions exhibited strong thixotropic behavior, especially at the highest CMC concentrations.     

Zero shear viscosity in miscible polymer blends of polystyrene and poly(2,6-dimethylphenylene ether)

The dynamic viscosities of blends of high molecular weight, narrowmolecular-weight distributed polystyrene and poly(2, 6-dimethylphenylene ether) are studied. The zero shear viscosity η_o depends on the weight average molecular weight M̄_w and on the average entanglement molecular weight M̄_e in the blend according to η_o ≈︁ M̄^3.4 _w(blend)/M̄^2.4_e(blend).     

Apparent Molar Volume and Viscosity Studies on Some Carbohydrates in Solutions

 The apparent molar volume (φ_v) and viscosity (η) of L(+)-arabinose, D(+)-galactose, D(−)-fructose, D(+)-glucose, sucrose, lactose, and maltose in water and in 0.1% and 0.3% water-Surf Excel solutions were measured as a function of solute concentrations at 308.15, 313.15, and 323.15 K, respectively. The apparent molar volume (φ_v) of the carbohydrates was found to be a linear function of the concentration. From a φ_v versus molality (b) plot, the apparent molar volume at infinite dilution (), which is practically equal to the partial molar volume at infinite dilutions () of these substances was determined. The viscosity coefficients B and D for the carbohydrates were calculated on the basis of the viscosity of the solutions and the solvent using the Jones-Dole equation. The activation free energy for viscous flow (ΔG ^≠) of the solutions was also calculated using the Eyring equation. The carbohydrates showed structure making behaviour both in water and in water-Surf Excel solutions. When water-Surf Excel solutions and pure water solutions containing carbohydrate molecules are compared, the former were found to be more structured. The behaviour of these solutes in water and in water-Surf Excel solution systems is discussed in the light of solute–solvent interactions.     

Study of Micellar Behavior of SDS and CTAB in Aqueous Media Containing Furosemide—A Cardiovascular Drug

Sound velocity and density measurements of aqueous solutions of the anionic surfactant SDS (sodium dodecyl sulfate) and the cationic surfactant CTAB (cetyltrimethylammonium bromide) with the drug furosemide (0.002 and 0.02 mol⋅dm⁻³) have been carried out in the temperature range 20–40 °C. From these measurements, the compressibility coefficient (β), apparent molar volume (φ _v ) and apparent molar compressibility (φ _κ ) have been computed. From electrical conductivity measurements, the critical micelle concentrations (CMCs) of SDS and CTAB has been determined in the above aqueous furosemide solutions. From the CMC values as a function of temperature, various thermodynamic parameters have been evaluated: the standard enthalpy change (DH_m^o\Delta H_{\mathrm{m}}^{\mathrm{o}}), standard entropy change (DS_m^o\Delta S_{\mathrm{m}}^{\mathrm{o}}), and standard Gibbs energy change (DG_m^o\Delta G_{\mathrm{m}}^{\mathrm{o}}) for micellization. This work also included viscosity studies of aqueous solutions of SDS and CTAB with the drug in order to determine the relative viscosity (η _r). UV-Vis studies have also been carried for the ternary drug/surfactant/water system having SDS in the concentration range 0.002–0.014 mol⋅dm⁻³. All of these parameters are discussed in terms of drug–drug, drug–solvent and drug–surfactant interactions resulting from of various electrostatic and hydrophobic interactions.     

Apparent Molar Volume and Viscosity Studies on Some Carbohydrates in Solutions

Summary.  The apparent molar volume (φ_v) and viscosity (η) of L(+)-arabinose, D(+)-galactose, D(−)-fructose, D(+)-glucose, sucrose, lactose, and maltose in water and in 0.1% and 0.3% water-Surf Excel solutions were measured as a function of solute concentrations at 308.15, 313.15, and 323.15 K, respectively. The apparent molar volume (φ_v) of the carbohydrates was found to be a linear function of the concentration. From a φ_v versus molality (b) plot, the apparent molar volume at infinite dilution (), which is practically equal to the partial molar volume at infinite dilutions () of these substances was determined. The viscosity coefficients B and D for the carbohydrates were calculated on the basis of the viscosity of the solutions and the solvent using the Jones-Dole equation. The activation free energy for viscous flow (ΔG ^≠) of the solutions was also calculated using the Eyring equation. The carbohydrates showed structure making behaviour both in water and in water-Surf Excel solutions. When water-Surf Excel solutions and pure water solutions containing carbohydrate molecules are compared, the former were found to be more structured. The behaviour of these solutes in water and in water-Surf Excel solution systems is discussed in the light of solute–solvent interactions. Corresponding author. E-mail: chemistry_ru@yahoo.com Received March 19, 2002; accepted (revised) July 31, 2002 Published online February 24, 2003     

Hydrophobic Interactions of Methylureas in Aqueous Solutions Estimated with Density, Molal Volume, Viscosity and Surface Tension from 293.15 to 303.15 K

Density (ρ), viscosity (η), and surface tension (γ) for 0.005–0.25 mol ⋅ kg⁻¹ solutions of urea, 1-methylurea, and 1,3-dimethylurea solutions have been measured at intervals of 0.005 mol ⋅ kg⁻¹. Apparent molal volume (V _o, cm³ ⋅ mol⁻¹) and intrinsic viscosity coefficients (B and D) are calculated from the ρ and η values, respectively. Primary data were regressed and extrapolated to zero concentration for the limiting density (ρ ⁰), apparent molal volume (V _φ ⁰), viscosity (η ⁰), and surface tension (γ ⁰) values for solute–solvent interactions. The –CH₃ (methyl) groups of N-methylureas weaken hydrophilic interactions and enhance hydrophobic interactions, and the values of the ρ ⁰ and V _φ ^o reflect the intermolecular forces due to electrostatic charge, whereas the η ⁰ and γ ⁰ values reflect the frictional and surface forces. The B values depict the size of hydrodynamic sphere due to heteromolecular forces whereas D shows the effect of concentration. The molar surface energy (ΔE _m/sur) for dropwise flow was calculated from the γ values and decreases with concentration and temperature, but increases with –CH₃ weakening of the hydrophilic interactions and strengthening the hydrophobic interactions.     

VISCOSITY BEHAVIOR OF LACQUER POLYSACCHARIDE IN AQUEOUS SOLUTION

The dependence of measured viscosity on NaCl concentration (0.1 to 3.0M), pH (range of 2—13) and cadoxen composition w_(cad) (from 2% to 100%) for the lacquer polysaccharide in NaCl/cadoxen/H_2O mixture containing HCl or without were obtained. All the viscosity exponents γin the Mark-Houwink equations under three different solvent condition arc close to 0.5. The w_(cad) dependence of reduced viscosity ηsp/c confirms the single strand chain of the polysaccharide. As the γvalues close to 0.5 and values of unperturbed dimension _θ/M and [η] much smaller than those for usual linear polymers, these facts suggest that the polysaccharide chains in the aqueous solutions should be dense random coil owing to the highly branched structure.     

Rheological Behavior of Dope Solutions of Poly(acrylonitrile‐co‐itaconic acid) in N,N‐dimethylformamide: Effect of Polymer Molar Mass

The rheological behavior of dope solutions of poly(acrylonitrile‐co‐itaconic acid) or poly(AN‐co‐IA) is important from the point of view of deriving the spinning conditions for good quality special acrylic fibers. The viscosity of the resin dope is dictated by the polymer concentration, molar mass, temperature and shear force. The dynamic shear rheology of concentrated poly(AN‐co‐IA) polymer dope solutions in N, N‐dimethylformamide, in the molar mass (M¯_v) range of 1×10⁵ to 1×10⁶ g/mol, was investigated in the shear rate (γ′) range of 1×10¹ to 5×10⁴ min^?1. An empirical relation between η and M¯_v was found to exist at constant shear rate. The dope viscosity was dependent on the molar mass and the shear rate at a given temperature (T) and concentration. The polymer molar mass index of dope viscosity (m) was calculated as functions of concentration (c), shear rate and temperature. The m values increased with shear rate and temperature. A master equation relating m, with shear rate and temperature was derived for a given dope concentration. At higher shear rates, m tends to the value of 3.4, which is close to the molar mass index of viscosity reported for molten thermoplastics. m increased significantly with shear rate and nominally with temperature, while an increase in concentration decreased it. The onset of shear thinning of the dope shifted to a lower shear rate regime with an increase in polymer concentration and the molar mass. For a given value of molar mass, the increase in viscosity of the dope solution with polymer concentration was dependent on the shear rate.     

Electrospun cellulose acetate fibers: effect of solvent system on morphology and fiber diameter

This paper reports an investigation of the effects of solvent system, solution concentration, and applied electrostatic field strength (EFS) on the morphological appearance and/or size of as-spun cellulose acetate (CA) products. The single-solvent systems were acetone, chloroform, N,N -dimethylformamide (DMF), dichloromethane (DCM), methanol (MeOH), formic acid, and pyridine. The mixed-solvent systems were acetone–DMAc, chloroform–MeOH, and DCM–MeOH. Chloroform, DMF, DCM, MeOH, formic acid, and pyridine were able to dissolve CA, forming clear solutions (at 5% w/v), but electrospinning of these solutions produced mainly discrete beads. In contrast, electrospinning of the solution of CA in acetone produced short and beaded fibers. At the same solution concentration of 5% (w/v) electrospinning of the CA solutions was improved by addition of MeOH to either chloroform or DCM. For all the solvent systems investigated smooth fibers were obtained from 16% (w/v) CA solutions in 1:1, 2:1, and 3:1 (v/v) acetone–DMAc, 14–20% (w/v) CA solutions in 2:1 (v/v) acetone–DMAc, and 8–12% (w/v) CA solutions in 4:1 (v/v) DCM–MeOH. For the as-spun fibers from CA solutions in acetone–DMAc the average diameter ranged between 0.14 and 0.37 μm whereas for the fibers from solutions in DCM–MeOH it ranged between 0.48 and 1.58 μm. After submersion in distilled water for 24 h the as-spun CA fibers swelled appreciably (i.e. from 620 to 1110%) but the physical integrity of the fibrous structure remained intact.     

Rheological behavior of an elongated micellar solution at low and high salt concentrations

 The aim of this experimen-tal work is to investigate the mechanism responsible of the decrease of the zero shear viscosity at high inorganic salt content. We report the linear and some nonlinear rheological properties of aqueous worm-like micellar solutions of CTAB containing NaNO₃ salt. The zero-shear viscosity η₀ curve versus salt concentration exhibits a well-defined maximum. We choose two salt concentrations (low and high) having the same zero-shear viscosity, and carefully explore the rheological characteristics and their evolutions in (and around) these two situations. The experimental results presented here, without excluding the possibility of the connections, suggest the possibility that the decreasing of η₀ is a result of the reduction in size of the worm-like micelles. Received: 16 February Accepted: 8 June 1998     

A note on overpotential dependence of AC impedance data

Charge-transfer resistance [R _ct = (dη/di)_{η = 0}] and Tafel plots of current density (i) versus overpotential (η) data are generally known to yield values of the energy-transfer coefficient (α) and exchange current density (i _o) of an electrochemical reaction. In the present investigation, the resistance (dη/di)_η≠0 that could be calculated by differentiating a wide range of i−η curves was also shown to provide the values of α and i _o, by plotting ln(dη/di)_η≠0 against η. Since α and i _o could also be evaluated directly from the experimental DC polarization data, the procedure was not of significant importance. Nevertheless, it was considered important in evaluating α and i _o from AC impedance data, because the procedure was based on data analysis, which was much simpler than that reported in the literature. A cobalt electrode prepared from fine metal powder was used in 1 M KOH electrolyte and the hydrogen evolution reaction was studied by AC impedance at several potentials. The resistance values measured from the complex plane impedance diagram were plotted against the potential, and the values of α and i _o were evaluated. Received: 8 October 1998 / Accepted: 11 January 1999     

Temperature dependence of viscosity for sucrose laurate/water micellar systems

The viscous behavior of sucrose laurate aqueous systems of high hydrophilic-lipophilic balance up to a 50% (wt) surfactant concentration at temperatures between 5°C and 60°C has been studied. Systems up to a 45% (wt) surfactant concentration show Newtonian behavior. The influence of temperature was studied using the activated diffusive relaxation model described by Goodwin. A maximum specific viscosity that appears at lower temperature as sucrose laurate concentration increases can be observed. These results are related to the micellar growth of the sucrose laurate aggregates as temperature rises. More concentrated systems show complex viscous response. Thus, a limit viscosity at low shear rates and a shear-thinning behavior after a critical shear rate are observed. Limit viscosity decreases and critical shear rate increases as temperature rises. This behavior is related to the threshold micelle concentration for entanglement of rod-like micelles.Nomenclature A Parameter of the equation that relatesE and temperature - B Pre-exponential factor of the Arrhenius equation - C Sucrose ester concentration (kg · m^–3) - CMC Critical micelle concentration - E Activation energy for long-range diffusive motion (Goodwin model) - E _a Activation energy of the viscous flow (Arrhenius equation) - E ₀ Parameter of the equation that relatesE and temperature - HLB Hydrophilic/lipophilic balance of the sucrose ester - J Constant that depends on the aqueous phase viscosity and mean micellar radius - k Boltzmann's constant - k ₁ Parameter of the Goodwin equation - k ₂ Parameter of the Goodwin equation - q _rel Contribution of the hydrodynamic interactions - R _e External radius of the sensor system - R _i Inner radius of the sensor system - T Temperature - T _max Temperature at the maximum viscosity - Newtonian viscosity - _i Intrinsic viscosity - _rel Relative viscosity = _solution/_water - _red Reduced viscosity = _sp/C - _sp Specific viscosity = _rel – 1 - ₀ Zero-shear-rate viscosity     

Welding dynamics in an atomistic model of an amorphous polymer blend with polymer–polymer interface

We consider an atomistic model of thermal welding at the polymer-polymer interface of a polyetherimide/polycarbonate blend, motivated by applications to 3D manufacturing in space. We follow diffusion of semiflexible chains at the interface and analyze strengthening of the samples as a function of the welding time t_w by simulating the strain–stress and shear viscosity curves. The time scales for initial wetting, and for fast and slow diffusion, are revealed. It is shown that each component of the polymer blend has its own characteristic time of slow diffusion at the interface. Analysis of strain–stress demonstrates saturation of the Young's modulus at t_w = 240 ns, while the tensile strength continues to increase. The shear viscosity is found to have a very weak dependence on the welding time for t_w > 60 ns. It is shown that both strain–stress and shear viscosity curves agree with experimental data.     

Characterization of water-soluble,cationic polyelectrolytes as exemplified by poly(acrylamide-co-trimethylammoniumethylethacryate chloride) and the establishment of structure-property relationships

The cationic copolymerization products of poly (acrylamide-co-trimethylammoniumethylmethacrylate chloride (PTMAC) having cationic monomer percentages of 8%, 25%, and 50% as well as the cationic homopolymer, were characterized with respect to their molecular dimensions. The light-scattering and viscometric measurements were carried out for molecular weights ranging from 200 000 to 12 800 000 g/mol in 1 M NaCl solution at 25°C. It was possible to establish a relationship between the molecular weight and the two parameters: intrinsic viscosity and radius of gyration, for all four polymers.Rheological investigations of the flow properties in 1 M NaCl solution were also carried out using the polymer with a cationic monomer of 50% (PTMAC 50). Structure-property relationships were formulated which made it possible to describe and predict the shear viscosity, both in the zero-shear region (Newtonian region) and in the shear-dependent region (non-Newtonian region) as a function of the polymer concentration, the molecular weight, and shear rate.Abbreviations a exponent of the []-M relationship - A ₂ 2^nd virial coefficient/mol·cm³·g^–2 - AAm acrylamide - b slope of the flow-curve in the shear-rate dependent region - c concentration/g·cm^–3 - dn/dc refractive index increment/cm³·g^–1 - f function - K constant of the []-M relationship/cm³·g^t-1 - m _c proportion of cationic monomers/mol % - M molecular weight/g·mol^–1 - M _w weight-average molecular weight/g·mol^–1 - M _n number-average molecular weight/g·mol^–1 - NaCL sodium chloride - PAAm polyacrylamide - PS polystyrene - PTMAC poly(acrylamide-co-trimethylammoniumethylme thacrylate chloride) - R_G ^20.5 radius of gyration/nm - TMAC trimethylammoniumethylmethacrylate chloride - shear rate/s^–1 - critical shear rate/s^–1 - viscosity/Pa·s - 0 zero-shear viscosity/Pa·s - _s solvent viscosity/Pa·s - _sp specific viscosity - [] intrinsic viscosity/cm³·g^–1 - relaxation time/s     

Study on the shear viscosity behavior of keratin/PEO blends for nanofibre electrospinning

Graessley's theory has been applied to keratin/PEO concentrated aqueous solutions giving qualitative insight to the rheology of these polymer blends in electrospinning. The shear rate dependent viscosity of different blends was compared with that of pure polymer solutions. The characteristic time τ_η was calculated by the minimum value of at the beginning of the non‐Newtonian viscosity behavior. Flow curves of PEO (at concentration from 1.0 to 7.0 wt %) reduce to a single curve by plotting η/η₀ against . Moreover, PEO solutions exhibit a linear proportionality between zero‐shear viscosity and the characteristic time η₀ ∝ τ_η. Keratin/PEO blend solutions follow the same proportionality at very high and low keratin content, whereas linearity drops when the keratin content range from 50 to 70%. The departure from the theory has been interpreted as a sign of some interaction between the macromolecules of keratin and PEO. It was supposed that keratin displaces solvent molecules and expands the PEO chain coils increasing the relaxation time of the polymer solution. This behavior was correlated with changes in the morphology of the nanofibres produced by electrospinning from these polymer blends. Finally, additive rules to zero‐shear viscosity were applied to keratin and PEO solutions, indicating that the experimental η₀ values were higher than the theoretical ones for all the proportions of the blends, especially for high keratin amount. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1193–1201, 2008     

Volumetric and Viscometric Studies on Some Inorganic Electrolytes in Water and in Water-SDS Solution Systems

The apparent molal volumes (φ _v ) of NaCl, NaNO₃, NH₄Cl, CuCl₂, CuSO₄, CoSO₄ and MgSO₄ in water and in water-SDS (Sodium dodecyl sulphate) solutions were determined from density measurements at 308.15, 313.15 and 323.15 K respectively. The limiting apparent molal volume at infinite dilution φ ^o _v which is practically equal to the partial molal volume V ^o ₂) of these electrolytes were found to be higher in water-SDS solution systems than those in water solutions. Viscosity coefficients (A and B) for these systems were also determined by Jones-Dole equation. All these electrolytes, except NH₄Cl exhibit structure making behaviour in water and in water-SDS solutions. Ammonium chloride showed structure breaking properties in water and in 0.01 molar water-SDS solutions. In 0.1 molar SDS solution, it showed structure making behaviour at the temperature range studied. The properties of these electrolytes in water and in water-SDS solution systems have been discussed in terms of the charge, size and hydrogen bonding effect.     

Frequency dispersion of the viscoelastic properties of solutions of electrolytes

Analytical expressions obtained earlier are used to numerically calculate the dynamic coefficients of the bulk η_ν(ω) and shear η _s (ω) viscosity and the corresponding modules of their bulk K(ω) and shear μ(ω) elasticity at a certain choice of the model of solution structure in an approximation of the osmotic solution theory. The potential energy of the interaction between ions Φ _ab (r) was taken as the sum of the Lennard-Jones potential and the generalized Debye potential, taking into account the configuration and size of ions. In this approximation, the viscoelastic properties of the NaCl water solution were numerically calculated over a wide interval of change in the thermodynamic parameters and frequency ranges. Satisfactory agreement with the literature experimental data was obtained.     

Solution viscosity behavior of complexes of poly(γ-benzyl-L-glutamate) with lightly sulfonated polystyrene or its zinc salt

The rheological behavior of solutions containing blends of poly(γ-benzyl-L -glutamate) (PBLG) and either the free acid or the zinc salt of lightly sulfonated polystyrene (SPS) was studied as a function of blend composition, polymer concentration, degree of sulfonation of the SPS, and the polypeptide molecular weight. The zinc salt of SPS formed a transition metal complex with the amine-end groups of the PBLG, and this resulted in an enhancement of the solution viscosity relative to a weighted average of the viscosities of the individual polymer solutions. The ZnSPS/PBLG solutions showed no anomalous time or shear dependencies. In contrast, solutions containing PBLG and the sulfonic acid derivative of SPS also had enhanced viscosities, but in addition, they exhibited time-dependent viscosities (thixotropic behavior) and shear thickening (dilatant behavior). This was attributed to a nonequilibrium structure of the interpolymer complex due to a competition between acid-amine and acid-ester interactions. Although the acid-amine interaction is enthalpically favored, when sufficient sulfonic acid groups were available, interactions between the sulfonic acid and the glutamate ester side groups of PBLG developed and this interaction promotes a helix-to-coil transition of the PBLG. ©1995 John Wiley & Sons, Inc.     

Dynamic scaling for gelation of a thermosensitive chitosan-β-glycerophosphate hydrogel

This paper investigates the thermal gelation of a chitosan-β-glycerophosphate system using rheometry. The gelation, performed for two polymer concentrations, was achieved in isothermal conditions to examine the effect of various temperatures (between 35 and 65 °C) on the sol-gel transition. The oscillatory shear data was used to verify the scaling behavior (G′ ~ G″ ~ ω ⁿ ) at the gel point, and the power-law index n was found to be dependent to some extent on chitosan concentration and temperature. The solutions zero shear viscosity (η ₀) and the gels low frequency modulus (G _e) were analyzed in terms of the relative distance to gelation time (ɛ). The two properties showed power–law relationships with ɛ, i.e., η ₀ ~ ɛ ^−s and G _e ~ ɛ ^z, and the indexes slightly increased with temperature. The dynamic scaling theory predicts a relationship between the indexes, i.e., n  =  z/(z  +  s), and this was in reasonably good agreement with the experimental findings.     

Aggregation and disaggregation of Aeromonas gum in an aqueous solution under different conditions

The aggregation and disaggregation of Aeromonas (A) gum, an acidic heteropolysaccharide, were investigated by viscometry, a fluorescent probe, and gel permeation chromatography combined with laser light scattering techniques in aqueous solutions containing desired NaCl at different temperatures. The A gum had a strong tendency of aggregation and high viscosity in the aqueous solutions. The weight‐average molecular weight, z‐average radius of gyration, weight‐average molar number (w_ag), and apparent aggregation number (N_ap) of the aggregates were investigated and discussed. The results indicated that there were three regions that corresponded to three kinds of aggregates and two transition temperatures at about 35 and 75 °C in the disaggregation course. When the temperature was higher than 75 °C, the w_ag hardly changed, and there was still a certain amount of aggregates even at 100 °C, indicating that the aggregates were difficult to disrupt completely. Moreover, the aggregation was thermally irreversible. Decreasing polysaccharide concentration reduced the content of the aggregate. However, N_ap remained constant around 20, independent of the polysaccharide concentration in a 0.5 M NaCl aqueous solution at 25 °C. At a salt concentration greater than or equal to 0.05 M, the aggregation was almost independent of the salt concentration used here. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2644–2651, 2000