Behavior Of Dilute Solutions Research Articles

‘Weak gel’ properties of khan flour from Belschmiedia sp.—a traditional food thickener from tropical West Africa

Khan flour from Belschmiedia sp. has a long history of use in tropical West Africa as a food thickener. The polysaccharide fraction, which is the principal constituent of the flour, shows typical polyelectrolyte behaviour in solution, giving an intrinsic viscosity of[η] = 6.4 dl/g in 0.1 mol/dm 3 NaCl. The solutions comply with the general form of shear thinning observed for disordered polysaccharide coils, with close Cox—Merz superposition of η *(ω) and η ( γ ˙ ) . The concentration dependence of ‘zero shear’ specific viscosity, however, shows departure from dilute solution behaviour at c[η] ≈ 2.5, in comparison with the typical value of ≈4.0 for most disordered polysaccharides, and the slope of log η sp versus log c at higher concentrations is unusually steep (≈4.2, in comparison with the usual value of ≈3.3). Similar behaviour has been reported previously for plant galactomannans, and attributed to chain—chain associations augmenting physical entanglement. Khan flour hydrates readily in water, and at concentrations within the approximate range 3–6% wlv gives ‘weak gel’ properties similar to those of ordered xanthan ( G′ > G″; little frequency dependence in either modulus; η * ( ω ) > η ( γ ˙ ) . The gel-like character decreases with decreasing concentration, and is attributed to weak interactions between swollen particles within a surrounding matrix of dissolved polysaccharide.

Viscoelastic properties of dilute nematic mixtures containing cyclic and hyperbranched liquid crystal polymers dissolved in a nematic solvent

AbstractThe twist and bend viscosities of dilute solutions of cyclic and hyperbranched liquid crystal polymers (LCP) dissolved in low molar mass nematic solvents were determined via dynamic light scattering analysis. These results were compared to those of linear chains with similar chemical repeat structures. The nematic solvent used was 4′‐pentyloxy‐4‐cyanobiphenyl (50CB). The cyclic LCP oligomers, Cy TPB10, have a mesogenic group, 1‐(4‐hydroxy‐4′‐biphenyl)‐2‐(4‐hydroxyphenyl) butane, separated by flexible decamethylene spacers. The twist viscosity of the cyclic Cy‐TPB10 oligomers increases with molecular weight more strongly than the linear, TPB‐10, suggesting that the hydrodynamic behavior of Cy‐TPB10 is closer to that of a rigid rod than TPB10. Surprisingly, the intrinsic bend viscosity [ηbend] of Cy‐TPB10 decreases with molecular weight, in contrast to the positive dependence for linear TPB10. This may reflect the higher strain energy in the smaller ring sizes. The hyperbranched LCP, TPD‐b‐8, is also based on the mesogen 10‐bromo‐1‐(4‐hydroxy‐4′‐biphenyl)‐2(4‐hydroxyphenyl) decane but with octyl groups at the chain ends. We compare the viscoelastic behavior of dilute nematic solutions of TPD‐b‐8 in 50CB against that of a linear main‐chain LCP, TPB7, with the same mesogenic group but with heptamethylene spacers. The viscometric properties of TPD‐b‐8/50CB and TPB7/50CB are quite different. The results suggest that each chain is prolate (i. e., R∥ > R⊥) but that TPD‐b‐8 has a smaller chain anisotropy than that of TPB7. © 1995 John Wiley & Sons, Inc.

Generalized Rouse model for a dilute solution of clustered polymers

A theory analogue to tha of Rouse is given, to describe the rheological behavior of dilute solutions consisting of clusters of crosslinked polymers. The frequency-dependent behavior of the dynamic moduli of these fluids differs substantially from that of the well-known Rouse-like fluid (G′∼G′∼ω1/2). In our case the storage modulus becomes proportional to ω3/2, while the loss modulus is proportional to ω. The loss modulus dominates the dynamic behavior for frequencies smaller than the largest normal frequency of the clusters.

Molecular characterization of polysaccharides dissolved in Me 2NAc-LiCl by gel-permeation chromatography

Polysaccharides function in key roles in textiles, biomass, foodstuffs, and plant cell walls, in addition to pharmaceuticals and immunological interactions. Structural information is urgently needed, but the complexity of the polymers, their interactions, and poor solubility have been limiting aspects. The dilute solution behavior of polysaccharides representing typical classes of natural products was investigated via gel-permeation chromatography (GPC) using refractive index and viscometric detectors. The solvent of choice for high-molecular weight cellulose analysis, dimethylacetamide with lithium chloride (Me 2NAc-LiCl), was used for direct polysaccharide dissolution without extraction or derivatization. The utility of this aprotic solvent for effective characterization of carbohydrates was explored. The polysaccharides studied spanned a range of molecular sizes, branching configurations, and linkage types, i.e., celluloses, amyloses, amylopectins, dextrans, pullulans, and curdlan. In addition to molecular weight values and distributions, calculated parameters defining each polysaccharides' dilute solution characteristics (intrinsic viscosity, radius of gyration, Mark-Houwink coefficients) were determined. Comparison between polysaccharides of similar molecular weight differing either in their branching patterns or linkage distribution were made. The calculated values were correlated with theoretical results predicted in the available literature and/or with known results. Relations among polymer linkage type, molecular chain compositions, branching assessments, and solution properties are described.

Solution rheology of mesquite gum in comparison with gum arabic

Commercial samples of mesquite gum and food-grade gum arabic were purified by filtration, alcohol precipitation, and extensive dialysis, and their Theological properties were characterised over the full range of concentrations at which solutions could be prepared (up to ~50% w/w). Both gave typical solution-like mechanical spectra, with close Cox-Merz superposition of η (⋗g) and η ∗(ω) and only slight shear thinning at the highest accessible concentrations, and (ln η rel) c varied linearly with log c from below 2% w/w to above 50%. The intrinsic viscosity of mesquite gum ([η]≈ 0.11 dl g −1) was appreciably lower than that of gum arabic ([η]≈ 0.19 dl g −1 in 0.1 m NaCl at 20 °C), and was independent of ionic strength above I ≈ 0.05, indicating a compact structure capable of only limited contraction. Departures from dilute-solution behaviour (η ~ c 1.4) occurred at c [η]≈ 1 for both materials, with a progressive increase in concentration dependence at higher space-occupancy, behaviour typical of soft, deformable particles, rather than of interpenetrating macromolecules. The increase in viscosity with increasing concentration was steeper for mesquite, consistent with evidence from size-exclusion chromatography and dynamic light scattering that the larger (and presumably more deformable) ‘wattle blossom’ component of gum arabic was absent from the mesquite gum sample.

Rheological properties of dextran related to food applications

Chemical, physical and mechanical properties of dextran were evaluated to assess the potential use of this microbial polysaccharide in food applications. Dextran demonstrated high solubility characteristics and promoted low solution viscosities. Newtonian behaviour was observed at concentrations <30% w/w for dextran (mol. wt 500 000). Higher mol. wt ‘native’ dextran solutions demonstrated slight pseudoplasticity at concentrations >1.5% w/w. Dilute and concentrated solution behaviour indicated the conformation of dextran in solution is dependent on both molecular weight and polysaccharide concentration. At low concentrations dextran (mol. wt 500 000) demonstrated properties typical of a ‘random coil’ polysaccharide. Increased concentration resulted in the polymer chain adopting a more compact coil geometry. Non-Newtonian behaviour observed in ‘native’ dextran solutions (>1.5% w/w) is attributable to the formation of inter-chain entanglements through polymer size effects and unique branching properties. Dextran (mol. wt 500 000) demonstrated two critical concentrations ( c * = 4.7% and c ** = 19% w/v); quasi-elastic light scattering measurements verified the coil overlap region ( c * ~ 4.6% w/v). Dynamic oscillatory evaluations indicated dextran (mol. wt 500 000) solutions exhibited dilute solution characteristics at concentrations <20% (w/w) and obeyed the empirical Cox—Merz rule. ‘Native’ dextran solutions (10–15% w/w) demonstrated mechanical spectra typical of concentrated polysaccharide solutions. Calorimetric analysis of ternary dextran:sucrose:water solutions demonstrated that dextran addition modified the frozen system behaviour of sucrose solutions. Increasing dextran concentration effectively increased the onset of melting temperatures ( T g ) by as much as 12°C.

Brownian dynamics of rigid polymer chains with hydrodynamic interactions.

With the idea of a broad investigation of the flow behavior of dilute polymer solutions in mind, the dynamics of polymer chains with rigid constraints and hydrodynamic interaction is formulated in various equivalent ways. Starting from a very general diffusion equation of polymer kinetic theory, equivalent stochastic differential equations of motion both in terms of generalized coordinates and in terms of constraint conditions are derived. Then an efficient Brownian dynamics simulation algorithm is constructed rigorously, and a convenient expression for evaluating stresses in simulations is suggested. Furthermore, a modified simulation algorithm, which is appropriate for infinitely stiff rather than rigid systems, is discussed.

Importance of Chemical Mismatch in Tricritical Polymer Solutions

Using a renormalization group analysis for the tricritical behavior of dilute polymer solutions with many chemically different polymers, we show that the chemical mismatch is indeed important. This is contrary to the irrelevance of chemical mismatch in good solutions. We find the second virial coefficients at the tricritical point to vanish with chain length L as L -1/2 [ln(L/a)] -9/11 , where a is the small cut-off. behavior is in a different universality class from the one for the tricritical solutions of polymers of the same chemical type. The generalization to block copolymers is also addressed

Water soluble copolymers. 54: N‐isopropylacrylamide‐co‐acrylamide copolymers in drag reduction: Synthesis, characterization, and dilute solution behavior

AbstractCopolymers of N‐isopropylacrylamide (IPAM) and acrylamide (AM) have been synthesized by free radical polymerization in deionized water using potassium persulfate as the initiator. Copolymer compositions were obtained by elemental analysis and 13C NMR. An r1r2 value of 0.99 indicates ideal copolymerization with random incorporation of the comonomers in the copolymers. Weight average molecular weights, second virial coefficients, diffusion coefficients, and average diameters were obtained via classical and quasielastic low angle laser light scattering. The molecular weights for all the copolymers and the homopolymers of IPAM and AM ranged from 2.2 × 106 to 5.2 × 106 g/mol. The second virial coefficients in deionized water increased with increasing acrylamide content in the copolymers. The dilute solution properties of the copolymers were studied by turbidimetry, microcalorimetry and viscometry. All the copolymers, with the exception of IPAM‐40 (the copolymer synthesized with 40 mole% IPAM in the feed), showed lower critical solution temperatures below 100°C. The solution studies were performed in deionized water, 0.514 M NaCl, and 1 M urea. The properties of the IPAM copolymers were influenced by both hydrophobic associations and hydrogen bonding. In 0.2% (∼7mM) sodium dodecyl sulfate, the alkyl chain of the surfactant molecules associates with the IPAM moieties on the copolymer backbone, leading to high intrinsic viscosities and the elevation of the LCST above 100°C.

Water-Soluble Polymers. 60. Synthesis and Solution Behavior of Terpolymers of Acrylic Acid, Acrylamide, and the Zwitterionic Monomer 3-[(2-Acrylamido-2-methylpropyl)dimethylammonio]-1-propanesulfonate

Terpolymers of acrylic acid (AA), acrylamide (AM), and the zwitterionic monomer 3-[(2-acrylamido-2-methylpropyl) dimethylammonio]-1-propanesulfonate (AMPDAPS) have been prepared by the free-radical polymerization in a 0.5 M NaCl aqueous solution using potassium persulfate as the initiator. The feed ratio of AMPDAPS:AA:AM was varied from 5:5:90 to 40:20:20 mol%, with the total monomer concentration held constant at 0.45 M. Terpolymer compositions were obtained by [sup 13]C NMR. Low-angle laser light scattering provided molecular weights and second virial coefficients which varied from (3.0 to 7.9) [times] 10[sup 6] and (2.23 to 2.95) [times] 10[sup [minus]4] ml mol g[sup [minus]2], respectively. The solubilities of the resulting terpolymers are dependent on pH as well as the amount of AMPDAPS and AA present in the feed. At pH 4 and for higher incorporation of AA and AMPDAPS in the feed (>25 mol %), the terpolymers are insoluble in deionized water and 0.25 M NaCl. At pH 8, all terpolymers are soluble in deionized water and salt solutions. The dilute and semidilute solution behavior f the terpolymers were studied as a function of composition and added electrolytes. Polyelectrolyte behavior was observed for all terpolymers at pH 8 as evidenced by a viscosity decrease in the presence of addedmore » electrolytes. The terpolymers exhibit higher viscosities in the presence of NaSCN versus NaCl. Comparison of the solution behavior of the terpolymers to copolymers of AM and AA as well as copolymers of AMPDAPS and AM has been made.« less

Viscometric behaviour of polymer blends based on poly (vinylidene fluoride)

The viscosity behaviour of dilute dimethylformamide solutions of poly(vinylidene fluoride)-poly (methyl methacrylate) and poly(vinylidene fluoride)-polystyrene has been studied at 25°C. The polymer concentration ranges are such that neither phase separation nor microgel formation occurs, although we are very close to theta conditions. The intrinsic viscosity and viscosity interaction parameter of the ternary mixtures have been calculated. The estimation of the compatibility of the above polymer pairs has been studied based on: a) specific viscosities; b) viscosity interaction parameters, according to Krigbaum and Wall formalism, and c) viscosity interaction parameters of a system formed by a dilute probe polymer in the presence of a matrix polymer and a small molecule solvent.

End-Functionalized Block Copolymers of Styrene and Isoprene: Synthesis and Association Behavior in Dilute Solution

Di- and triblock copolymers of isoprene and styrene having a highly polar sulfozwitterion group on one or both ends of the chain were prepared by anionic polymerization using high-vacuum techniques with [3-(dimethylamino)propyl]lithium as initiator. The dimethylamino end group of the chain was transformed to a zwitterion by reaction with cyclopropanesultone. The monofunctional zwitterion-capped copolymers were found to associate in CCl 4 (a good solvent for polystyrene and polyisoprene) whereas the difunctional versions formed gels even below the coil overlap concentration c * . The aggregation number was found to decrease with increasing base molecular weight due to the excluded vulume repulsions of the copolymeric tails

Thermodynamic consideration on phase behavior of the ternary two-phase system of water, nonane, and ethylene glycol monobutyl ether

The phase behavior of a ternary two-phase system composed of water, nonane, and ethylene glycol monobutyl ether (C4E1) was investigated thermodynamically. The compositions of the water and nonane phases were measured precisely as a function of the total concentration of C4E1 and temperature under atmospheric pressure by gas liquid chromatography. A new kind of criterion of ideality for the two-phase equilibrium was proposed and examined by using the composition data obtained. The composition region of ideal dilute solution behavior was determined for the two phases as a function of temperature. It was suggested that the formation of the aggregate of C4E1 in the water phase is enhanced at lower temperatures and that in the nonane phase at higher temperatures, respectively

Tricritical theory of dilute polymer solutions with quenched disorder

We have performed a renormalization group analysis of the tricritical behavior of dilute polymer solutions containing quenched impurities in three dimensions. We have treated the quenched disorder using the replica formalism. The logarithmic corrections to the mean field results for the quenched problem are found to be in a different universality class from those for the pure or annealed problem. For example, the leading corrections to the second virial coefficient and the specific heat are proportional to L1/2(ln L/a0)−2/11 and L(ln L/a0)7/11, respectively, where L is the chain length and a0 is the cutoff; the coexistence curve is found to follow the universal equation u∼−𝒞(‖ln 𝒞2a0‖)−9/11 when 𝒞2a0≪1, where 𝒞 is the monomer concentration and u is the two-body excluded volume interaction parameter.

Combined collapse-swelling behavior of acrylamide gel in polymeric solution.

It is found that acrylamide gel shows combined collapse-swelling behavior in dilute aqueous solution of poly(vinyl methyl ether) when transferred from the equilibrium swelling state in pure water. Namely, it starts to collapse quickly and then it is swollen again with its volume approaching the original value in water. The phenomenon can be explained by thermodynamic analysis of osmotic pressure. The re-swelling is caused by the penetration of linear polymer into the network. The analysis can also explain differences of the collapsing and re-swelling behavior between samples with different shapes.

Reversible electrode potentials for formation of solid and liquid chlorozirconate and chlorohafnate compounds

The standard electrode potentials for the formation of the pure solid and molten compounds Li2ZrCl6, Li2HfCl6, Na2ZrCl6, Na2HfCl6, K2ZrCl6, K2HfCl6, Cs2ZrCl6, and Cs2HfCl6 have been calculated from measured vapour pressures corresponding to their thermal decomposition at equilibrium and from available thermochemical data. Reversible potentials for the formation of Na2ZrCl6 and of K2ZrCl6 in solution according to the reaction[Formula: see text]where A is Na or K, have been calculated from available equilibrium vapour pressures as functions of the mole fractions of the alkali hexachlorocompounds. Standard potentials for the above reaction and "formal" potentials are also given. The latter are useful in predicting the electrochemical behaviour of dilute solutions of the hexachlorozirconates in alkali metal chlorides.

Dilute solution behavior of polystyrene latex particles and their interaction with Triton X 100

Dilute solution behavior of polystyrene latex particles and their interaction with Triton X 100

Shear‐thickening behavior of dilute polymer solutions: Kinetic interpretation

An equation of the kinetic of the formation of reversible associations of macromolecules in flow is proposed. The results are compared with experimental data which were derived from viscosity measurements displaying a shear‐thickening behavior of dilute polymer solutions.

Properties of polyelectrolytes—2. Poly(monoethyl itaconate), conformational and viscometric behaviour in dilute solution

The dilute solution behaviour of poly(monoethyl itaconate) (PMEI) has been studied in 2-ethoxyethanol, methanol, dimethylsulfoxide and water, at 298 K, by intrinsic viscosity and light scattering measurements, and size exclusion chromatography (SEC). Weight-average molecular weight was determined in methanol. PMEI shows typical polyelectrolyte behaviour. The Kuhn-Mark-Houwink-Sakurada relationships were established in the media studied. The conformational parameters (σ and C ∞) and the thermodynamic parameter ( B) were calculated. The results are compared with previous studies of poly(monomethyl itaconate).

Thermal behavior of Landolt reactions in comparatively dilute aqueous solutions followed by heat exchange calorimetry of batch type

In batch-type Landolt reactions composed of potassium iodate and sodium hydrogen sulfite, the color of the solution changes suddenly at a time interval after mixing the component substances. This is often presented as chemical magic with the nickname “clock reaction”. The thermal behavior of more dilute solutions than in the demonstration is studied by heat exchange calorimetry of batch type. Sample and reference vessels are fixed differentially in a precision water bath. Heat evolved in the vessel is exchanged freely with the surrounding water. Crystalline sodium hydrogen sulfite is added to an aqueous solution of potassium iodate to start the reaction. The temperature change in the vessels is detected by a thermistor, and treated by an analogue computation to obtain the rate of heat evolution and total heat effect. The heat of reaction Q reac is estimated after correction for the negative heat of solution of sodium hydrogen sulfite. Free iodine may be produced after the consumption of sodium hydrogen sulfite, if [NaHSO 3] init, is not larger than three times [KIO 3] init Q reac increases in direct proportion to [NaHSO 3 init in the region of excess [KIO 3] init However, as expected, constant values of Q reac were observed in the region of excess [NaHSO 3] init when it is more than 3.6 times larger than [KIO 3] init. The reaction enthalpy at infinite dilution was estimated to be −228.4 kJ per 1 mole of [NaHSO 3] init.