Rheological Properties Of Concentrated Solutions Research Articles

Rheological properties of concentrated solutions of fucoidan in water and in an ionic liquid

Dynamic viscoelasticity has been examined for concentrated solutions of fucoidan from Cladosiphon okamuranus in water and in an ionic liquid 1-butyl-3-methylimidazolium acetate (BmimAc). The existence of the electrostatic interaction between fucoidan chains in the aqueous solutions and its disappearance in the BmimAc solutions have been clearly shown by the difference in the terminal flow behavior between the aqueous and BmimAc solutions. On the other hand, the rubbery plateau indicating the entanglement coupling between fucoidan chains has been observed for both solvents at rather high concentrations. The molecular weight between entanglements (Me) for fucoidan in the BmimAc solutions has been determined from the plateau modulus at several concentrations and then Me for fucoidan in the molten state (Me,melt) has been estimated to be 1.0 × 104 as a measure of the specific chain characteristics of fucoidan.

Elucidating the Effects of Metal Complexation on Morphological and Rheological Properties of Polymer Solutions by a Dissipative Particle Dynamics Model

When a salt is added to a polymer solution, metal cations may coordinate with polymer ligands forming interchain and intrachain links. Metal coordination leads to drastic changes of polymer morphology, formation of clusters, and, ultimately, a sol–gel transition that affect the solution rheology. Although metal coordination is ubiquitous in polymeric systems, the physical mechanisms of coordination-induced morphological and rheological changes are still poorly understood due to the multiscale nature of this phenomenon. Here, we propose a coarse-grained dissipative particle dynamics (DPD) model to study morphological and rheological properties of concentrated solutions of polymers in the presence of multivalent cations that can coordinate the polymer ligands. The coordinating metal is introduced as a 3D complex of planar, tetrahedral, or octahedral geometry with the central DPD bead representing the metal cation surrounded at the vertices by either four or six dummy beads representing coordination sites, s...

Rheological properties of concentrated solutions of gelatin in an ionic liquid 1-ethyl-3-methylimidazolium dimethyl phosphate

Rheological properties of gelatin solutions were examined in concentrated regions. Gelatin species from porcine skin and from bovine bone were dissolved in an ionic liquid 1-ethyl-3-methylimidazolium dimethyl phosphate. The dynamic viscoelasticity data for the solutions exhibited rubbery plateaus, indicating the existence of entanglement coupling between gelatin chains in the solutions. From the analogy with rubber elasticity, assuming that the molecular weight between entanglements (Me) is the average mesh size of the entanglement network, Me for gelatin in the solutions were determined from the heights of the rubbery plateaus. Then the value of Me in the molten state (Me,melt), a material constant reflecting the chemical structure of polymer species, for gelatin was estimated to be 8.7×103. Compared to synthetic polyamides whose Me,melt were known, Me,melt for gelatin was significantly larger, which could be explained by the densely repeating amide bonds composing gelatin.

Some remarks on rheological properties of concentrated solutions of galactomannans

Rheological properties of concentrated solutions of galactomannans, locust bean gum (lb-gum) and guar gum (g-gum), were compared between samples from different manufacturers to examine the effects of prescreening for polysaccharides. The angular frequency dependence curves of the storage and loss moduli were similar in shape between lb-gum samples but were different quantitatively. This results in different values of the molecular weight between entanglements in the molten state (Me,melt) for the lb-gums, although Me,melt is a material constant. On the other hand, Me,melt for g-gum samples agreed with each other. It was demonstrated that the quantitative difference in the rheological properties of lb-gum solutions was attributed to the effective lb-gum concentration in the solutions and that Me,melt is surely a material constant even for these galactomannans. This study confirms that prescreening of samples is very important for polysaccharides to estimate Me,melt.

Rheological properties of concentrated solutions of galactomannans in an ionic liquid

The rheological behavior of galactomannans in concentrated solutions was examined by using dynamic viscoelasticity measurements. Concentrated solutions of three galactomannans, guar gum, tara gum, and locust bean gum were prepared with an ionic liquid 1-butyl-3-methylimidazolium chloride as the solvent. Each galactomannan solution showed angular frequency dependence curves of the storage modulus and the loss modulus which were characteristic of a solution of entangled polymer chains. The molecular weight between entanglements (Me) was obtained from the plateau modulus and the concentration dependence of Me showed Me in the molten state (Me,melt) to be 4.6×103, 3.2×103, and 2.7×103 for guar gum, tara gum, and locust bean gum, respectively. It was found that the material constant Me,melt depends on the mannose/galactose ratio of the galactomannans. The number of monosaccharide units between entanglements in the molten state for the galactomannans varied within the range found for other polysaccharides such as cellulose and agarose in ionic liquids, suggesting that all the galactomannans take a random-coil conformation in ionic liquid solutions.

Rheological properties of concentrated solutions of agarose in ionic liquid

AbstractThe rheological properties of agarose solutions were examined under the effect of entanglement coupling between agarose chains. Agarose solutions were prepared by using an ionic liquid 1‐butyl‐3‐methylimidazolium chloride as a solvent. The concentration of agarose was varied from 1.1 × 101–2.1 × 102 kg m−3. The master curves of the angular frequency (ω) dependence of the storage modulus (G′) and the loss modulus (G″) showed a rubbery region in the middle ω region and a flow region at low ω region, respectively. The molecular weight between entanglements (Me) for agarose was calculated from the plateau modulus. Moreover, Me for agarose melt was determined to be 2.3 × 103 from the concentration dependence curve of Me. By using well‐known empirical relations in polymer rheology, information on molecular characteristics of sample agarose was derived. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Rheological properties of concentrated solutions of high-molecular-weight polyacrylonitrile in dimethyl sulfoxide

The rheological properties of concentrated solutions of polyacrylonitrile in dimethyl sulfoxide are studied in steady and dynamic regimes of shear flow as a function of the molecular–mass characteristics of the polymer. It is found that as the molecular mass of PAN increases, the elastic component of the solution viscosity increases more rapidly than the viscous component; this is one of the main reasons for the instability of the formation and structural nonuniformity of fibers.

Rheological properties of concentrated solutions of cellulose and its mixtures with other polymers in orthophosphoric acid

We have investigated the specific features of the steady shear flow of concentrated spinning solutions of cellulose and its mixtures with polyvinyl alcohol, chitosan, and polyacrylonitryl in orthophosphoric acid in the temperature range of 303–323 K. Rheological curves including highest- and lowest-viscosity regions have been obtained. The influence of the nature of the polymer additive and its content on the profile of rheological curves of the cellulose solution has been established.

Rheological properties of concentrated solutions of gellan in an ionic liquid

The rheological properties of solutions of gellan were examined at high concentrations where there is entanglement coupling between gellan chains. An ionic liquid 1-butyl-3-methylimidazolium chloride (BmimCl) was used as a solvent. Concentrated solutions of gellan in BmimCl were obtained by using a hot-molding technique. The concentration of gellan was varied from 1.9 × 10 2 to 4.8 × 10 2 kg m −3. The measurement temperature ranged from 50 to 100 °C. The master curve of the angular frequency dispersion of the storage modulus for the gellan solutions showed a rubbery plateau at high angular frequency. The molecular weight between entanglements ( M e) for gellan was obtained from the plateau modulus. From the concentration dependence curve of M e, M e for gellan in the molten state was determined to be 2.3 × 10 3.

Synthesis and properties of epoxy derivatives of syndiotactic 1,2-polybutadiene

Samples of modified 1,2-polybutadiene were prepared by the reaction of the polymer with peracetic acid or tert-butyl hydroperoxide in the presence of a catalyst, hexacarbonylmolybdenum. The hydrodynamic characteristics of dilute solutions and the rheological properties of concentrated solutions of the starting and epoxidized polydiene in hydrocarbon solvents were studied. The Huggins constant K x, second virial coefficient A 2, root-mean-square size of macromolecular coils $$(\overline {R^2 } )^{1/2} $$ , and the enthalpy, entropy, and Gibbs energy of activation of the viscous flow of solutions of the starting and modified polydiene were estimated.

Rheological properties of concentrated solutions of carboxymethyl starch

Carboxymethyl starch was synthesized by the esterification of starch with monochloroacetic acid in ethanol as a reaction medium. Three samples of carboxymethyl starch having different degrees of substitution were prepared. The influence of temperature on the viscosity of concentrated carboxymethyl starch solutions, as well as the dynamic-mechanical properties of the concentrated solutions were investigated. The activation energy of viscous flow was determined and it was found that it decreased with increasing degree of substitution. The results of the dynamic-mechanical measurements showed that solutions of starch and carboxymethyl starches with higher degrees of substitution behave as gels. Values of the storage modulus in the rubbery plateau were used to calculate the molar masses between two points of physical crosslinking, the density of crosslinking and the distance between two points of crosslinking.

Rheological Properties of Concentrated Solutions of Mixtures of Lemon Pectin with Flexible-Chain Vinyl Polymers

Rheological properties of concentrated aqueous solutions of lemon pectin, polyvinylpyrrolidone, polyvinyl alcohol, and 1 : 1 blends of lemon pictin with these polymers were studied at 25-70°C.

Rheological Properties of (Meth)acrylic Cross-Linked Polymer Microparticles, 2. Role of Interactions in Non-Reactive and in Reactive Diluents. Copolymerization Studies

The rheological properties of (meth)acrylic cross-linked polymer microparticle solutions have been studied regarding the influence of physical interactions. Cross-linked polymer microparticles (CPM) were synthesized with different functionalities: epoxy, acrylic, carboxyl, hydroxyl, octadecyl and methyl. The viscosities of either dilute or concentrated solutions in non-reactive solvent (xylene) and in reactive solvents (styrene and isobornyl acrylate monomer) have been measured for each type of CPM. A very weak effect of functionality was noticed on the intrinsic viscosity of CPM, whatever the solvent. Only carboxyl groups had a significant influence by increasing the viscosity because of hydrogen bonding. Greater effects were shown on the rheological properties of concentrated solutions. All solutions exhibited shear-thinning behavior when the solvent was xylene or styrene. Carboxyl functionalized CPM still led to higher viscosity, while octadecyl groups reduced the low shear limiting viscosity. The recovery time was strongly increased for CPM with epoxy and acrylic functionalities when styrene was used instead of xylene, whereas it remained the same for all other CPM solutions. In isobornyl acrylate monomer, only CPM functionalized epoxy and acrylic showed shear-thinning behavior, the other solutions being Newtonian. Finally a copolymerization study has been done on three solutions, containing either non-reactive CPM in reactive diluent, or reactive CPM in non-reactive diluent, or reactive CPM in reactive diluent. This study confirmed the cross-linking mechanism of acrylic systems. First, intramolecular reaction took place within the CPM and small aggregates were formed. Then these aggregates interconnected leading to a viscoelastic solid.

Properties of Concentrated Solutions of Fibroin and Its Derivatives

Rheological properties of concentrated solutions of fibroin from natural silk and its chemically and physically modified derivatives were studied. The structure and properties of these solutions, which have characteristically anomalous viscous flow, are determined by the degree and type of modification.

Rheological properties of concentrated solutions of ternary acrylonitrile copolymers

Rheological properties of concentrated solutions of ternary acrylonitrile copolymers

Hydrogel composition based on carboxymethylcellulose and agar-agar

The results are given of a study of the rheological properties of concentrated solutions of CNC and agar-agar and the influence of their quantitative ratio on the anomalous flow behavior of their solutions. A hypothesis is put forward of the formation of intermolecular associates from CMC and agar-agar which leads to the formation of a stronger structural network of solutions of the initial polysaccharides.

Viscoelastic and rheological properties of concentrated solutions of proteoglycan subunit and proteoglycan aggregate

The oscillatory and steady shear rheological properties of concentrated solutions of proteoglycan subunit (PGS) and aggregate (PGA) from bovine articular cartilage have been studied using a Rheometrics fluids spectrometer. At comparable concentrations in the physiological range tan delta increases from 0.5 to 1.0 for PGA as the oscillation frequency (omega) increases from 10(-1) to 10(2) rads/s, compared to a decrease from 40 to 5 for PGS. Thus PGA solutions exhibit predominantly elastic response whereas those of PGS exhibit primarily viscous behavior. PGA solutions show pronounced shear-thinning behavior at all shear rates (gamma) in the range 10(-2) less than gamma (s-1) less than 10(2), whereas PGS solutions exhibit predominantly Newtonian flow. For PGA, the small-strain complex viscosity eta* (omega) is substantially smaller than the steady-flow viscosity eta(gamma) at comparable values of omega and gamma. These observations indicate that the presence of proteoglycan aggregates leads to formation of a transient or weak-gel network. Since aggregation leads to a large increase in molecular hydrodynamic volume and hence in the relaxation times for macromolecular rotation, it appears that role of aggregate formation is to shift the linear viscoelastic response from the terminal viscous flow into the plateau elastomeric regime of relaxational behavior. Normal or pathological changes that produce a decrease in aggregation will result in a loss of elastomeric behavior of the proteoglycan matrix.

Rheological properties of concentrated cellulose solutions in N-methylmorpholine-N-oxide

-- Rheological properties of concentrated solutions of cellulose in N-mcthylmorpholine-N-oxide on varying the concentration of cellulose in the solution from 10 to 28% by wt. have been studied. -- It has been found that on increasing the cellulose content of the solution, the viscoelastic properties of the solution qualitatively change. -- In spinning highly concentrated solutions (cellulose content greater than 20%) an abrupt impairment takes place in stability of jet formation; this is connected with a change in supermolecular structure and elastic properties of the solution.

Phase state, structure and rheological properties of concentrated solutions of the polyblock copolymer of polyarylene sulphone oxide and polybutadiene in selective solvents

The link between tke phase state, structure and rheological properties of concentrated solutions of the polyblock copolymer of a polyarylene sulphore oxide and polybutadiene with increase in the selectivity of the solvent has been studied. The phase diagram of the system block copolymer-solvent-selective precipitant has been obtained. The specifics of the equilibrium swelling of the block copolymers in mixtures of good and selective solvents determined by the partial destruction of the domains has been established.

The influence of different unit structures related to asymmetry of one of the monomers on polyamidobenzimidazole properties

From comparative studies of thermodynamic rigidity, rheological properties of concentrated solutions, ability to form intermolecular hydrogen bonds and also of phase transitions from the isotropic to the liquid crystalline state it has been shown that polyamidobenzimidazoles of regular and irregular unit structures hardly differ from another.