Reduced viscosity of aqueous solution

In Figure 8, the reduced viscosity of aqueous solutions of the monomeric cationic surfactant is... 

The relativeand reduced viscosities of aqueous solutions of poly(maleic acid) neutralized with NaOH increase as the degree of neutralization is increased, reaching a peak at the half-neutralization point, and then decrease. 

The degradation rate of chitosan in aqueous solutions increases with detreasing polymer concentration (Figure 31.1). It is mainly caused by the enhanced "OH mobility rising with the reduced viscosity of diluted solution (Wasikiewicz et al. 2005b). Moreover, in diluted solutions the distance between... 

Hyaluronidase activity was originally determined biol( cally by the intradermal spread of colored indicator solutions and chemically by the reductometric method. The purification of hyaluronidase and the study of its mechanism of action depended on the development of assay methods more accurate than the spreading effect and less time consuming than the determination of reducing substances. New methods were based on certain high polymeric properties of hyaluronic acid (a) the viscosity of aqueous solutions of the polysaccharide, and (b) the formation of mucin clots with acidified proteins. 

Pfansteil and Her demonstrated that as the K2O-P2O5 ratio is reduced from 0.998, the influence of cross-linking in solutions of Kurrol s salt diminishes, if it is not eliminated entirely. The behavior expected for very long linear chains persists after the expected behavior for cross-linkages is gone, as judged from viscosities of aqueous solutions obtained from salts with K2O--P2O5 ratios well below 0.98. 

Polyelectrolytes are used to modify the interaction (i.e., to increase electrostatic repulsion) between particles when absorbed on a surface. They are used in hair conditioners to coat hairs and reduce static (conditioners also contain silicones to provide a smooth coating on the hair surface). Polyelectrolytes also modify the viscosity of aqueous solutions and are extensively used as emulsifiers and thickeners. Polyelectrolyte gels based on polyacrylates are used as super-absorbent gels (termed hydrogels) in baby nappies (diapers, US). The materials are able to swell up to many... 

The second system described by Lovrien, which belongs to mechanism (2), is poly(methacrylic acid) with pendant azobenzene groups. In aqueous solution, the viscosity was found to increase by ultraviolet irradiation. Matejka et. al, have developed the system to styrene -maleic anhydride copolymer with pendant azobenzene groups. The copolymer exhibited a pronounced photodecrease of the viscosity in 1,4-dioxane solution, i.e. a reversible decrease by 24 - 30 % in the reduced viscosity of the solution after ultraviolet irradiation. In THF, the viscosity decreased by 1 - 8 %. The contraction of the dimensions of the copolymer coil is explained as follows trans to cis isomerization induces a strong dipole in the azo bond. These dipoles become mutually oriented and attract each other so that compact coil conformations are preferred. In the dark, the viscosity of the copolymer solution returned to the original value as shown in Figure 3. The increase rate of the viscosity, however, was much slower, by a factor of 1/2.5 to 1/7, than the rate of cis to trans isomerization of the pendant azobenzene chromophores measured by optical absorption in the dark. The discrepancy requires further examination of the postulated mechanism of the conformational change. 

The microphase separation of an amphiphilic polyelectrolyte is clearly reflected in the viscosity behavior of its aqueous solution. As a representative example, Fig. 5 shows the reduced viscosities of ASt-x with different styrene (St) content plotted against the polymer concentration in salt-free aqueous solution [29], The AMPS homopolymer and its copolymers with low St content exhibit negative slopes, which is the typical behavior of polyelectrolytes in the concentration range shown in Fig. 5. With increasing St content, however, the slope systematically decreases and eventually turns to be slightly positive, while reduced viscosity itself markedly decreases. These data indicate that, with increasing St content, the... 

Table 1 contains details of experimental conditions used in the preparation of the polyethers. It can be seen that the reduced viscosity of the polymers which were obtained increased with the concentration of the aqueous KOH solution and was inversely related to the amount of dibromomethane used in the reaction. 

Polvcondensation of DHTN with dibromomethane under phase transfer conditions. The polycondensation of DHTN [13.13g, 0.080 mole] with 32mL dibromomethane was carried out in the presence of tetrabutyl ammonium bromide [2.48g or 0.008 mole] and 160mL 60 wt% aqueous KOH solution with vigorous stirring at room temperature for 24h. The polymer was precipitated in methanol and purified by reprecipitation from THF solution into distilled water to afford 13.51 g (94.8%) of the desired polyether which exhibits a reduced viscosity of 0.27 dL/g [measured at 30°C in DMF at a concentration of 0.5g/dL]. The polymer had an IR spectrum with a prominent C-O-C peak at 1210 cm". The NMR spectrum of the polyether [CDC13] showed peaks atff 1.7-2.5 (C-CH2-CH2-C), 4.6-5.3 (0-CH2-0), and 7.3-8.0 (aromatic). 

Proteins can be modified by proteolytic enzymes with limited reduction in their nutritional bioavailability. Enzymatic hydrolysis of peptide bonds of proteins will reduce their molecular size, affect their structures, expose different regions of their molecules to the environment, and thereby alter their contribution to functionality, e.g. by increasing and decreasing the solubility and viscosity properties, respectively, of aqueous solutions. These changes can be controlled by carefully selecting proteolytic enzymes, maintaining proper treatment conditions, and monitoring the hydrolysis reactions. 

The surface tension of aqueous solutions of PVA varies with concentration, temperature, degree of hydrolysis, and acetate distribution on the PVA backbone. Surface lension decreases slightly as the molecular weight is reduced. The relationship between the intrinsic viscosity and molecular weight changes with degree of hydrolysis of the polymer. 

In several previous papers, the possible existence of thermal anomalies was suggested on the basis of such properties as the density of water, specific heat, viscosity, dielectric constant, transverse proton spin relaxation time, index of refraction, infrared absorption, and others. Furthermore, based on other published data, we have suggested the existence of kinks in the properties of many aqueous solutions of both electrolytes and nonelectrolytes. Thus, solubility anomalies have been demonstrated repeatedly as have anomalies in such diverse properties as partial molal volumes of the alkali halides, in specific optical rotation for a number of reducing sugars, and in some kinetic data. Anomalies have also been demonstrated in a surface and interfacial properties of aqueous systems ranging from the surface tension of pure water to interfacial tensions (such as between n-hexane or n-decane and water) and in the surface tension and surface potentials of aqueous solutions. Further, anomalies have been observed in solid-water interface properties, such as the zeta potential and other interfacial parameters. 

The dilution of solutions33 containing equimolar ratios of monomer units of the complex components results in the dissociation of the complexes of PMAA with low-molecular weight PEG. The reduced viscosity of solutions rapidly increases, which indicates the existence of the equilibrium PMAA + PEG complex. In the case of a relatively high-molecular weight PEG, the PMAA macromolecules are firmly connected with PEG and at the dilution of aqueous solution, an increase of the reduced viscosity typical of polyelectrolytes does not occur, i.e. the complex does not dissociate. The absence of temperature dependence of the relative viscosity in the temperature range 15-40 °C is indicative of the stability of this complex (Fig. 4). 

Some papers60-61 have been devoted to phase separation of polyionic complexes from partially furated (PVA-S) and aminoacetylated (PVA-AAC)poly(vinyl alcohol) in aqueous salt solutions. The separation liquid-liquid or complex coacervation occurs at a definite value of the charge density on the macromolecule. From the concentration dependence of the reduced viscosity of the initial components PVA-S, PVA-AAc and their equivalent mixture in water it follows that the viscosity of the components noticeably increases with dilution, and the curve of the equivalent mixture is concentration independent. This fact confirms the formation of the neutral polymer salt, due to electrostatic interactions of PVA-S (strong polyadd) and PVA-AAc (weak polybase). 

Many salts reduce the viscosity of aqueous acacia solutions, while trivalent salts may initiate coagulation. Aqueous solutions carry a negative charge and will form coacervates with gelatin and other substances. In the preparation of emulsions, solutions of acacia are incompatible with soaps. 

The distribution coefficient, K, of a solute for an equilibrium between the aqueous phase and micelle, or the micellar solubilization, depends on temperature generally, the distribution coefficient decreases with an increase in temperature. This means that the migration time of a solute, will be reduced when the temperature is elevated under typical micellar electrokinetic chromatography (MEKC) conditions, where, for example, sodium dodecyl sulfate (SDS) is employed as a pseudo-stationary phase at a neutral condition (i.e., pH 7). Also, the velocity of the electro-osmotic flow (EOF), Meof> and the electrophoretic velocity of the micelle, (me), will be increased by an increase in temperature because of a reduced viscosity of the micellar solution employed in a MEKC system. 

Concentrations and types of sugars or oligosaccharides also affect the viscosity of pectin solutions. Chen and Joslyn (1967) and Kar and Arslan (1999a) found that sucrose, dextrose and maltose increased the viscosity of aqueous pectin solutions whereas dextrins reduced it. The viscosity-enhancing effect of the sugars was interpreted in terms of the decrease in dielectric constant of the solvent, dehydration action and hydrogen bonding formation. However, the effect of dextrins on the viscosity of pectin was apparently an artifact due to ionic impurities in the dextrin. 

Another characteristic viscosity behavior of polyelectrolyte solution, viz., the effect of added salts, has been reported for ionomer solutions [55]. The reduced viscosity of sulfonated PS (Li salt) in DMF increases markedly with decreasing polymer concentration in the absence of added salt, LiCl. However, as the concentration of LiCl increases, the reduced viscosity significantly decreases, then a maximum appears in the viscosity curve, and finally straight lines are obtained. The last behavior is characteristic of neutral polymer solutions. Table 3 summarizes ionomer nonaqueous solutions whose viscosity behavior has been reported. Those results have demonstrated that the viscosity behavior of random ionomers is basically similar to that of polyelectrolyte aqueous solutions. 

---