Search results for "VISCOSITY"
showing 10 items of 542 documents
Molecular association in water-isomeric pentanol mixtures at 25�C
1982
The results of static dielectric constant and viscosity measurements on solutions of water (concentration range 0 to 0.3 mole fraction) in 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol, and 2-methyl-2-butanol together with previous results for solutions of water in n-pentanol are discussed in terms of the information that they provide on the nature and the extent of molecular association in these solutions. We conclude that in most systems this association leads to the formation of tetrahedral complexes such as H2O(ROH)4. Evidences of the correlation of water-alcohol interactions with molecular parameters (position of OH group, steric hindrance of alkyl chain) of alcohols a…
A novel and simple method for the purification of extracellular levansucrase from Zymomonas mobilis.
2003
A new and simple method for the purification of extracellular levansucrase from Zymomonas mobilis from highly viscous fermentation broth was developed. After incubation of the fermentation broth with a fructose-polymer cleaving enzyme preparation (Fructozyme, Novozymes, DK) for 48 h, levansucrase precipitated as aggregates and was redissolved in a 3 M urea solution. By ongoing size-exclusion chromatography on Sephacryl S-300 the final levansucrase preparation was purified 100-fold and exhibited a specific activity of 25-35 U/mg(protein). The levansucrase was stable in 3 M urea solution for at least four months without inactivation. To maximize the enzyme yield the dynamic changes of extrace…
Mechanistic Understanding of Food Effects: Water Diffusivity in Gastrointestinal Tract Is an Important Parameter for the Prediction of Disintegration…
2013
Much interest has been expressed in this work on the role of water diffusivity in the release media as a new parameter for predicting drug release. NMR was used to measure water diffusivity in different media varying in their osmolality and viscosity. Water self-diffusion coefficients in sucrose, sodium chloride, and polymeric hydroxypropyl methylcellulose (HPMC) solutions were correlated with water uptake, disintegration, and drug release rates from trospium chloride immediate release tablets. The water diffusivity in sucrose solutions was significantly reduced compared to polymeric HPMC and molecular sodium chloride solutions. Water diffusivity was found to be a function of sucrose concen…
Ascorbic Acid Oxidation in Sucrose Aqueous Model Systems at Subzero Temperatures
2004
The reduction of Tempol by ascorbic acid in concentrated sucrose solutions was measured by electron paramagnetic resonance (EPR) at temperatures ranging from 16 to −16 °C. This method allowed the determination of the rate constants (k) of this fast reaction, by recording the Tempol reduction as a function of time. The two reactants were initially separated and had to migrate for the reaction to occur. The experimental findings were compared with predicted values according to the equation for diffusion-controlled reaction proposed by Atkins. The experimental reaction rate constants were observed to be lower than the calculated ones. However, the experimental values were found to be controlle…
On the significance of molecular surfaces and thermodynamic interactions for the excess viscosities of liquid mixtures
1994
The viscosities η of homogeneous binary mixtures of liquids are usually approximated as In η = ϕ1 In η1 + ϕ2 In η2 where ϕi and ηi are the volume fractions and the viscosities, resp., of the i-th pure substance; the behavior of real systems is then discussed in terms of Δ In η, the deviations from the above reference behavior. Here a semi-empirical approach is presented according to which volume fractions are replaced by the surface fractions Ωi to create a more realistic reference state, and the thermodynamic interaction parameter g is taken into account. The new equation reads (expressing it for practical purposes still in the terms of ϕi) γ is a geometric factor, measuring the difference…
Influence of the electrical interface properties on the rheological behavior of sonicated soy lecithin dispersions
2006
A significant effect, on the rheological behavior, due to the electrical properties of vesicles formed from concentrated soy lecithin dispersions have been studied in this work. The rheopectic behavior of concentrated soy lecithin dispersions (120, 150, 180, 210 and 240 g L−1) prepared by swelling–light sonication–freezing–unfreezing procedure is studied and it is specially emphasized on the transition under steady shear from lamellar phase of planar sheets to closed structures as multilamellar vesicles. Samples have been exposed to a different number of sonication cycles (from 0 to 100) and the changes in the hysteresis loop area, the apparent viscosity and the electrophoretic mobility hav…
A proposed equation of correlation for the study of thermodynamic properties (density, viscosity, surface tension and refractive index) of liquid bin…
2009
Abstract The literature on the physicochemical properties of liquid binary mixtures shows that most such systems exhibit nonlinear behavior. As a result, rigorous data and equations capable of affording a reliable estimate of the behavior of such mixtures are needed. The present study offers an equation of correlation providing a reliable estimation of the properties (density, viscosity, surface tension and refractive index) of binary mixtures of liquids as a function of mole fraction. In order to assess the validity of the proposed equation, the latter has been applied to reference binary mixtures, and comparisons have been made of the experimental values of the studied magnitudes versus t…
Binding of Na+ ions to proteins: Effect on taste perception
2015
Abstract This study investigated the relationship between the ionic binding of sodium and salty perception in protein matrices. Protein type (i.e. gelatin, milk protein and soy protein), protein concentration and pH were varied to obtain matrices with distinct compositions and rheological properties. 23Na NMR spectroscopy was used to determine the ratio of sodium ions bound to proteins and the mobility of sodium ions. The results showed that protein type, concentration and pH affected the rheological properties of the protein matrices, the ionic binding of sodium ions and taste intensity. As the protein concentration increased, the mobility of sodium ions decreased and the ratio of bound so…
Solution properties of polyelectrolytes—V. Viscometric study of mixed polyanions in pure water
1990
Abstract A viscometric study of sodium polystyrene sulphonate (NaPSS) and sodium poly( l -glutamate) (NaPLG) in salt-free water has been carried out as a function of the total concentration, cm, and the concentration of one polyelectrolyte at fixed concentration of the other. The influences of the molecular weight and concentration are considered in order to establish the degree of compatibility. For the first time, an equation is proposed to define the reduced viscosity of the NaPSS + NaPLG mixture in water. The viscometric interaction parameter, Bm, taking into account the electrostatic and thermodynamic interactions between both polyions, is defined as a geometrical mean of the contribut…
Predictability of properties of ternary systems solvent/solvent/polymer from interaction parameters of the binary systems—III. Analysis of binary pot…
1990
Abstract The assumption that the ternary parameter, g τ , and its derivative with respect to polymer concentration, ( ∂g τ / ∂φ 3 ) μ 1 , φ 3 → 0 , can be described by three binary interaction parameters, g o i 3 ( i = 1, 2) and g 12 , implies that these must be independent functions. This feature has been demonstrated by using g o i 3 values obtained from A/B/polymer(P) and C/D/P ternary polymer systems to predict the ternary properties, namely preferential solvation (λ), second virial coefficient ( A 2 ) and intrinsic viscosity ([η]), of a A/C/P ternary system. Two distinct polymers, polystyrene(PS) and poly(dimethylsiloxane)(PDMS), have been utilized in three solvent mixtures, benzene(BZ…