Flow Behavior Of Aqueous Solutions Research Articles

Effect of Recombinant Spidroins Self-Assembly on Rheological Behavior of Their Dispersions and Structure of Electrospun Nanofibrous Materials.

The effect of primary amino acid sequence in recombinant spidroins on their spatial organization is crucial for the fabrication of artificial fibers and fibrous materials. This study focuses on the rheological properties of aqueous and alcoholic solutions of recombinant analogs of natural spidroins (rS1/9 and rS2/12), as well as the structure of their films and nanofibrous materials. Non-Newtonian flow behavior of aqueous solutions of these proteins was observed at certain concentrations in contrast to their solutions in hexafluoroisopropanol. The secondary structure of recombinant spidroins was addressed by IR spectroscopy, whereas their self-organization in various solvents was studied by AFM and cryo-TEM. The influence of the solvent on the structure and properties of the films and nanofibrous materials produced by electrospinning has been established.

Shear-induced phase transition in the aqueous solution of an imidazolium-based ionic liquid.

An ionic liquid (IL) is a salt in the liquid state that consists of a cation and an anion, one of which possesses an organic component. Because of their non-volatile property, these solvents have a high recovery rate, and, hence, they are considered as environment-friendly green solvents. It is necessary to study the detailed physicochemical properties of these liquids for designing and processing techniques and find suitable operating conditions for IL-based systems. In the present work, the flow behavior of aqueous solutions of an imidazolium-based IL, 1-methyl-3-octylimidazolium chloride, is investigated, where the dynamic viscosity measurements indicate non-Newtonian shear thickening behavior in the solutions. Polarizing optical microscopy shows that the pristine samples are isotropic and transform into anisotropic after shear. These shear thickened liquid crystalline samples change into an isotropic phase upon heating, which is quantified by the differential scanning calorimetry. The small angle x-ray scattering study revealed that the pristine isotropic cubic phase of spherical micelles distort into non-spherical micelles. This has provided the detailed structural evolution of mesoscopic aggregates of the IL in an aqueous solution and the corresponding viscoelastic property of the solution.

Ce(IV)-ion initiated grafting of 1,3 galactomannan biopolymer with acrylonitrile

Galactomannans based biopolymers are common constituents of ungerminated seeds of numerous leguminous plants present in endosperm of seeds. They are highly valuable in industries due to their ability to modify the flow behavior of aqueous solutions viz. thicken, suspend, gel, stabilize, swell and film formation. Consequently, they have diverse applications in food and non-food due to their biocompatibility, biodegradability, sustainability and abundance. Cassia occidentalis, an annual weed occurring throughout India is a rich source of seed galactomannans (∼30% endosperm). The gum derived from seed endosperm can be potentially utilized in a number of industries to replace the conventional expensive gums. However, the extracted gum has considerable disadvantages such as uncontrolled hydration, changes in viscosity during storage, pH-dependent solubility, lower shelf life etc, thereby, limiting their vast industrial applications. Intriguingly, these limitations can be overcome by functionalization of hydroxyl groups. Therefore, grafting onto C. occidentalis seed gum was carried out with acrylonitrile in presence of ceric ammonium nitrate under inert atmosphere. The reaction conditions were optimized by varying concentration of CAN, nitric acid, acrylonitrile, reaction temperature and time. The grafted gum was characterized using FTIR, TGA, DTG, X-Ray and SEM analysis.

Oscillatory and steady shear rheological properties of aqueous polyacrylamide solutions

Abstract Dynamic and steady shear data representing the flow behaviour of aqueous solutions of Polyacrylamide, in the concentration range of 0.25–0.6% wt./vol. and temperature range of 5–45 °C, have been reported. Maxwell model, Carreau model and power law model were used to represent the present experimental data. Rheological parameter such as fluid relaxation time (λ), representative of fluid elasticity, was evaluated by fitting the oscillatory shear data to the four element Maxwell model. Other rheological parameters such as flow behaviour index (n) and flow consistency index (K) were evaluated by fitting the steady shear data to the power law model in the relevant shear rate range. The shear dependent viscosity data are well represented by Carreau model. Predictive equations for λ, n and K are proposed by incorporating the combined effect of temperature and concentration. Presented data could be of great use in various engineering applications such as enhanced oil recovery.

The effect of high hydrostatic pressure on the flow behaviour of skim milk–gelatin mixtures

The flow behaviour of aqueous solutions of gelatin, and skim milk–gelatin mixtures treated by high-pressure processing (HPP) were investigated. HPP was carried out at 5 °C for 15 min, at 150 MPa, 300 MPa, 450 MPa and 600 MPa, and the gelatin concentrations were varied from 0 to 1 wt.%. Viscosity measurements showed that the HPP treatment did not affect the flow behaviour of gelatin alone, nor that of the skim milk–gelatin mixtures made with < 0.4 wt.% gelatin. However, at gelatin concentration > 0.4 wt.%, the mixtures treated with 300 and 450 MPa exhibited a peculiar flow behaviour, where at intermediate shear rates the viscosity was higher than that of the non-treated mixture or the mixtures treated at 150 MPa and 600 MPa. Particle size measurements showed that for gelled mixtures (> 0.4 wt.% gelatin) 300 MPa HPP treatment resulted in an increase in the particle size, while at all other pressure treatments (> 150 MPa), a shift in particle size distribution to lower sizes was observed. Confocal microscopy showed that these skim milk–gelatin mixtures were phase-separated with a gelatin continuous phase, this was confirmed by dynamic rheological measurements which showed that qualitatively the viscoelastic properties of the mixtures were the same. A mechanism of the effect of high-pressure treatment on the casein micelle in skim milk–gelatin mixtures is proposed. This fundamental work, dealing with the effect of high pressure on the physicochemical properties skim milk–gelatin mixtures could be relevant to the industry in several ways. Firstly, skim milk–gelatin mixtures are widely used in the dairy industry, particularly in yoghurt manufacture, where gelatine is used as a stabiliser. In addition the application of High Hydrostatic Pressure to such a system is also relevant, as this technology could be used as a substitute to the conventional heat treatment processes. Secondly, an important finding of this study is that under certain conditions of high pressure and gelatine concentration, an increase in viscosity is observed at intermediate shear-rate (between 10 and 100 s − 1 ). This is highly relevant to Industry if the system requires subsequent pumping. Thirdly, from a sensory view point, this range of shear rates (10 and 100 s − 1 ) is comparable to that experienced by a food bolus during swallowing. Thus, this effect of high pressure on the viscosity can influence sensory attribute of the skim milk–gelatin food system.

0510 金属イオンと水溶性ポリマー溶液の混合による粘稠性変化の実験的検討(OS5-2 非ニュートン流体の流動現象,オーガナイズドセッション)

Effects of ionic species on flow behavior of aqueous solutions of polyacrylamide (PAM) were experimentally investigated. Elastic property of PAM solution is transiently increased by addition of Fe^<3+> solution and then it is decreased to initial value. In order to elucidate this phenomenon, we investigated the Weissenberg effect of the solution. The phenomenon was explained by the interaction between Fe^<3+> and PAM solution.

Intrinsic Viscosity and Flow Behaviour of Arabic Gum Aqueous Solutions

The intrinsic viscosity and flow behaviour of aqueous solutions of different concentrations of Arabic gum were studied. The molecular weight of this polymer was calculated using the value of the intrinsic viscosity, employing both Huggins and Kramer and Mark-Houwink equations. The value of the apparent viscosity and the influence of the shear rate on the rheological behaviour of different polymer concentrations in aqueous solution were determined. The effect of temperature over the flow behaviour was also studied. The Ostwald model has been employed to fit the experimental data and model parameters have been obtained.

The effect of (2-hydroxypropyl)-β-cyclodextrin on rheology of hydrophobically end-capped poly(ethylene glycol) aqueous solutions

(2-Hydroxypropyl)-β-cyclodextrin (HPBCD), a modified cyclic oligosaccharide, changes the flow behavior of aqueous solutions of a model telechelic associative polymer, hydrophobically end-capped poly(ethylene glycol) (ODU-12), because the inclusion complexation of HPBCD and octadecyl end-capping groups interferes with aggregation of the polymer end groups. The HPBCD-induced decrease in the high-frequency modulus can be well described assuming a 1:1 binding isotherm, but cannot fully explain the decrease in the low shear rate Newtonian viscosity, because HPBCD also strongly decreases the relaxation time. Consequently, besides decreasing low shear rate Newtonian viscosity, HPBCD also extends the Newtonian behavior to higher shear rates as predicted by the free-path version of the transient network theory [Marrucci et al., Macromolecules 26, 6483–6488 (1993)].

Elongational Flow of Solutions of Poly(ethylene oxide) and Sulfonated Surfactants

In this work, the elongational flow behavior of aqueous solutions of poly(ethylene oxide) (PEO) was studied in the presence of sulfonated surfactants. The technique of opposed-jets flow was used to generate an elongational flow field in which pressure drops were measured as a function of strain rates. The surfactants used were sodium dodecyl benzene sulfonate (SDBS) and an α-olefin sulfonate (AOS). Solutions of PEO and other flexible polymers exhibit extension thickening in opposed-jets flow due to the formation of transient networks of entangled molecules. This effect is present at concentrations below the static coil overlap concentration, due to the changes in molecular conformation induced by the flow. When SDBS or AOS are added to PEO solutions at low concentrations, the extension thickening weakens due to an increase in PEO intramolecular interactions that lead to coil contraction. This occurs until the surfactant concentration is close to the critical aggregation concentration reported in the literature. Further addition of surfactant induces the formation of intermolecular interactions as the PEO molecules are expanded by the electrostatic repulsion between attached micellar aggregates, with an associated strengthening of extension thickening. Intramolecular effects were not seen beyond a specific PEO concentration.

Temperature-Induced Transitions from Rodlike to Globular Micellar Aggregates in Aqueous Cetyltrimethylammonium Bromide in the Presence of 9-Anthrylalkanols

The flow behavior of aqueous solutions of cetyltrimethylammonium bromide was investigated as a function of temperature (15−50 °C) in the presence of various amounts of three 9-anthrylalkanols: 9-anthrylmethanol; 9-(1-(1-hydroxy)ethyl)anthracene; 9-(1-(1-hydroxy-2,2,2-trifluoro)ethyl)anthracene. Changes from non-Newtonian flow to Newtonian flow were observed upon increasing the temperature or decreasing the content of the 9-anthrylalkanols. The temperatures (between 291 and 321 K) and concentration ratios, at which these changes were observed, are distinct for the three solubilizates. Evaluations of rheological and light scattering data are in accordance with the presence of very big globular micellar aggregates (diameters up to 35 nm) in the Newtonian and long rodlike aggregates (lengths up to 800 nm) in the non-Newtonian cases. Electron micrographs confirm this interpretation.

Effect of ethanol addition on the elongational flow behavior of aqueous solutions of poly(ethylene oxide)

In this work, we explore the effect of ethanol addition on the extension thickening behavior of aqueous solutions of poly(ethylene oxide) (PEO) in porous media and opposed-jets flow. The main aspect analyzed is the formation of transient entanglements of polymer molecules, which are responsible for the sudden increase in pressure drops and apparent extensional viscosities with strain rates observed in elongational flows of PEO solutions. The results show that changing the solvent by adding ethanol modifies the solution behavior because of two effects. First, the increase in the solvent viscosity increases the disentanglement time of the transient entanglements so that the onset of extension thickening occurs at lower strain rates in the presence of ethanol. Second, ethanol solutions are poorer solvents than water for PEO. This promotes intermolecular interactions between PEO coils when the solutions are semi-dilute. The net result is a lowering of the onset strain rate for extension thickening to values that are much smaller than those expected for the same PEO chains dissolved in a higher viscosity and poorer solvent. The results also show that coil-coil interactions in solution can be detected at lower concentrations in porous media flow than in opposed jets flow.

Rheological characterization of the dilatant flow behavior of highly substituted hydroxypropylmethyl- cellulose solutions in the presence of sodium lauryl sulfate

The flow behavior of aqueous solutions of three highly substituted, hydrophobic hydroxypropylmethylcelluloses (HPMC) in mixtures containing the anionic surfactant sodium lauryl sulfate (SLS) was investigated both rheo-mechanically and rheo-optically. For the first time it was possible to demonstrate dilatant flow in these systems, a phenomenon which is otherwise only known of some suspensions and associative thickening solutions. Without addition of SLS, the aqueous HPMC solutions showed the predicted flow behavior of polymer solutions, and the Cox–Merz rule was fulfilled. With the addition of SLS to these HPMC solutions, the least hydrophobic HPMC displayed no dilatancy. The solutions of a more hydrophobic HPMC with SLS exhibited on the one hand an increase in viscosity, and on the other hand shear thinning as well as shear thickening. The most hydrophobic HPMC displayed more clearly the effects of an SLS-dependent viscosity increase and the appearance of dilatant flow. At constant HPMC concentration (0.5% w/w), a maximum increase in viscosity (factor 15) was observed in the critical micelle concentration range for SLS. By rheo-optical measurements it was possible to detect an unusually pronounced alignment of the polymer segments as well as a sharp increase in the birefringence values, even before the macroscopic occurrence of dilatant flow. According to the existing network theories, this behavior of the aqueous solutions of highly substituted HPMCs in mixture with SLS has been interpreted as a shear-induced transition from intra-molecular to intermolecular interactions.

Studies on a purification method for locust bean gum by precipitation with isopropanol

A commercial sample of locust bean gum was dissolved in hot water, centrifuged, and the supernatant and the sediment were recovered. Part of the supernatant was freeze-dried and the rest was poured into isopropanol to yield a precipitate of purified gum. This precipitate was recovered and a part of it was subjected to a second purification with isopropanol; an almost pure galactomannan sample was obtained. Another sample of the crude gum was fractionated on the basis of its solubility in water at different temperatures. Five fractions were obtained with mannose to galactose ratios (M/G) increasing with the temperature of fractionation. The purified samples exhibited higher M/G ratios and number average molecular weights (M n) than the crude gum, whereas the opposite was observed with the freeze-dried sample. The polydispersity index decreased quite significantly in purified samples, meaning that they were more homogeneous than the original sample. Intrinsic viscosities were lower for the purified samplesv The flow behaviour of aqueous solutions of the gums was studied in the concentration range 0.6–1.2 g/dl: the solutions of the crude gum had higher viscosities than those of the purified and the freeze-dried gums at similar concentrations, throughout the shear rate range.

The behaviour of polymer solutions in extension-dominated flows, with applications to Enhanced Oil Recovery

The rheometry and flow behaviour of aqueous solutions of polyacrylamide and xanthan gum are discussed, with the expectation that the results will be of use in Enhanced Oil Recovery (EOR). The rheometrical study gives particular prominence to the dramatically high values of extensional viscosity which are possible in aqueous solutions of flexible polymers such as polyacrylamide. The effect of such factors as polymer concentration, salt concentration and mechanical degradation on rheometrical properties is outlined. Reference is also made to the qualitatively-different rheometrical behaviour experienced by comparable solutions of xanthan gum.

Rheological Properties of Leucaena glauca Gum in Aqueous Solutions

AbstractThe flow properties of Leucaena glauca gum solutions were studied in the range of shear rates 1.5 to 1310 s−1, using a rotational viscometer Rheotest 2. The flow behaviour of aqueous solutions of the polysaccharide is pseudoplastic, and transition from Newtonian to pseudoplastic behaviour occurs in the low shear rate range at concentrations of interest to the industry. The flow of polysaccharide solutions is described by equation of state proposed by M. M. Cross. The basic rheological parameters, like zero shear rate viscosity (ηo), infinite shear rate viscosity (ηα) and a constant associated with the rupture of linkages (α) were calculated applying simple and established relations. The effect of concentration and temperature on rheological parameters have been studied. The Cross equation is found to be applicable to the data with a good degree of accuracy over a wide range of shear rates.