Diffusivity and dissolution rate in polymeric solutions

Abstract

The diffusivity of benzoic acid was measured in various concentrations of aqueous solutions of methylcellulose, hydroxypropyl cellulose and guar gum. An increase in concentration of the polymer increases the viscosity of the polymeric solution to a greater degree than it decreases diffusivity. Dissolution rates of benzoic acid in various concentrations of polymeric solutions were measured. An equation is presented for calculating the relative dissolution rates in polymeric solutions.     

Hydrodynamics of Dissolution in a Newtonian and a Non-Newtonian Solution

The dissolution rate of benzoic acid was measured in various concentrations of aqueous solutions of propylene glycol and colloidal solutions of guar gum. In polymeric solutions of guar gum the dissolution rate was influenced primarily by the effect of viscosity on the hydrodynamic shear in the dissolution medium. In the aqueous solutions of propylene glycol the dissolution rate was a complex function of kinematic viscosity, solubility, diffusivity and rotational speed. By means of dimensionless analysis it appears that the difference in the hydrodynamics of the true and colloidal solutions causes a difference in dissolution rate because of dissimilar fluid flow patterns.     

Hydrodynamics of Dissolution in a Newtonian and a Non-Newtonian Solution

Abstract

The dissolution rate of benzoic acid was measured in various concentrations of aqueous solutions of propylene glycol and colloidal solutions of guar gum. In polymeric solutions of guar gum the dissolution rate was influenced primarily by the effect of viscosity on the hydrodynamic shear in the dissolution medium. In the aqueous solutions of propylene glycol the dissolution rate was a complex function of kinematic viscosity, solubility, diffusivity and rotational speed. By means of dimensionless analysis it appears that the difference in the hydrodynamics of the true and colloidal solutions causes a difference in dissolution rate because of dissimilar fluid flow patterns.     

Comparison of Several Diffusion Equations in the Calculation of Viscosity and its Relation to Dissolution Rate

The viscosity of polymeric solutions as measured by a rotational viscometer may not be the viscosity of the environment through which a solute molecule diffuses. By use of the Stokes-Einstein equation a viscosity, which is not affected by the mechanics of the viscometer, may be calculated if the size and diffusivity of the solute molecule are determined. The values of such viscosity calculated by using several diffusion equations compare favorably with the value calculated with the Stokes-Einstein equation. The dissolution rates of benzoic acid in aqueous solutions of three non-ionic suspending agents is related to the viscosity.     

Photothermal characterization and stability analysis of polymeric dye lasers

The millisecond heat dissipation of pump energy in polymeric, solid-state dye lasers has been studied with photothermal deflection spectroscopy (PTDS) to determine the contribution of that process to photodegradation of the active material. The samples were solutions of Rhodamine 6G in 2-hydroxyethyl methacrylate copolymerized with various amounts of methyl methacrylate or ethylene glycol dimethylacrylate to change the microstructure properties of the matrix. Values of the thermal diffusivity measured with PTDS were in the range 0.6-1.1 x 10(-3) cm(2) s(-1) for all the compositions studied here. A comparison of these values with previous optical data on lasing efficiency and photostability for the same samples indicates that the macroscopic rate of thermal diffusion is not the key factor that limits the efficiency and stability of these lasers, at least for low pump repetition rates (<1 Hz).     

Absorption of water vapour into falling films of aqueous lithium bromide

In this study, experiments have been performed for water vapour absorption into 50 and 60 mass% aqueous lithium bromide solution films flowing down a vertical surface to investigate the effects of liquid diffusivity values, molecular properties of the concentrated solutions and non-absorbable gases. The experimental results for wavy films over a film Reynolds number range of 15–90 indicate larger dimensionless mass transfer rates than for strictly laminar flow when the diffusivity of water in a concentrated lithium bromide solution is less than that in a dilute solution. The complete set of results shows that the physical property data for lithium bromide solutions including the diffusivities measured by Kashiwagi are sufficient to explain mass transfer behavior.     

A New Technique for Hydrate Thermal Diffusivity Measurements

Thermal property measurements of natural gas hydrates in various sediment mixtures are necessary to describe heat transfer to surroundings during well boring and gas production. An apparatus for measuring thermal diffusivity in various mixtures of hydrates with sediment has been constructed. The apparatus uses a new method for determining thermal diffusivity that has advantages over the von Herzen and Maxwell probe method. The new experiment is simple and inexpensive to construct and appears to be much more accurate than the ±30% reported for an earlier probe. The thermal diffusivity of ice has been measured to determine the uncertainty of the technique, i.e., within ±6% with a 95% confidence level. The thermal diffusivity for pure methane hydrate at various temperatures is reported. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

Dissolution of Manganese Oxides of Various Compositions in Sulfuric Acid Solutions Studied by Kinetic Methods

The dissolution of manganese oxides in sulfuric acid solutions of various concentrations has been studied by kinetic methods. We have investigated the dissolution of manganese oxides of various compositions in sulfuric acid solutions of various concentrations. The composition of the manganese oxides and the sulfuric acid concentration have been shown to influence the dissolution rate. We have calculated kinetic parameters of the dissolution of manganese oxides in sulfuric acid solutions (dissolution rate, activation energy for dissolution, and reaction orders) and proposed a model for the dissolution of manganese oxides in sulfuric acid solutions.     

Thermal and spectrophotometric studies of new crosslinking method for collagen matrix with glutaraldehyde acetals

Despite the many existing crosslinking procedures, glutaraldehyde (GA) is still the method of choice used in the manufacture of bioprosthesis. The major problems with GA are: (a) uncontrolled reactivity due to the chemical complexity or GA solutions; (b) toxicity due to the release of GA from polymeric crosslinks; and (c) tissue impermeabilization due to polymeric and heterogeneous crosslinks formation, partially responsible for the undesirable calcification of the bioprosthesis. A new method of crosslinking glutaraldehyde acetals has been developed with GA in acid ethanolic solution, and after the distribution inside de matrix, GA is released to crosslinking. Concentrations of hydrochloride acid in ethanolic solutions between 0.1 and 0.001 mol/L with GA concentration between 0.1 and 1.0% were measured in an ultraviolet spectrophotometer to verify the presence of free aldehyde groups and polymeric compounds of GA. After these measurements, the solutions were used to crosslink bovine pericardium. The spectrophotometric results showed that GA was better protected in acetal forms for acid ethanolic solution with HCl at 0.003 mol/L and GA 1.0%(v/v). The shrinkage temperature results of bovine pericardium crosslinked with acetal solutions showed values near 85 °C after the exposure to triethylamine vapors.     

New resorbable polymeric systems with antithrombogenic activity

The synthesis and application as resorbable coatings of vascular grafts of a new polyacrylic derivative of Triflusal (2-acetyloxy-4-trifluoromethyl)benzoic acid, a commercial drug with antithrombogenic properties, are described. The high-molecular-weight polyacrylic system is rather stable in physiological conditions and provides a chemical support for the slow release of the pharmacologically active compound, Triflusal, or its main metabolite (2-hydroxy-4-trifluoromethyl)benzoic acid (HTB). Experiments of deposition and retention of platelets in static basal conditions using plasma-rich medium from blood of sheep, seem to indicate that the polymeric coating of the polyacrylic derivative of Triflusal improves the antiaggregating character for platelets of the surface of small-diameter vascular grafts without the application of other antithrombogenic drugs.     

Dissolution Characteristics of Benzoic Acid and Salicylic Acid Mixtures in Reactive Media

The dissolution rates of mixtures of the two acids, benzoic acid and salicylic acid were determined in a phosphate buffered medium. Dissolution properties from compressed discs under sink conditions were essentially linear. Plots of dissolution rate versus compact composition deviated from the two component models for both non-interacting and interacting components. Dissolution rates, particularly for benzoic acid at intermediate weight fractions, were lower than predicted by the theory for two non-interacting components. These lower than expected rates were explained in terms of the physicochemical changes occurring in the microenvironment at the solid liquid interface.     

The role of Lewis acid-base processes in ligand-exchange chromatography of benzoic acid derivatives on zirconium oxide.

Porous microparticulate zirconium oxide shows very different selectivities and pH dependencies for the separation of benzoic acid derivatives than do conventional bonded-phase anion-exchange supports. This results from a very significant ligand-exchange contribution to the retention of hard Lewis bases on the surface of transition-metal oxide supports. We have found that the capacity factors of a wide variety of derivatives of benzoic acid are closely correlated with their Bronsted acidities. The eluent pH is also a critical factor in determining the magnitude of the capacity factor, but it does not have much influence on chromatographic selectivity. The differential selectivity of this phase in comparison to conventional polymeric and bonded-phase anion exchangers can be attributed to complexation and steric effects which profoundly alter the elution patterns of certain solutes.     

Isobaric Heat Capacity of Binary Solutions of Methyl and n- Hexyl Alcohols at High Pressures

The pulsed-regular mode is used to measure the isobaric heat capacity of solutions of methyl and n-hexyl alcohols at different temperatures, pressures, and concentrations. An empirical equation is suggested for the calculation of the isobaric heat capacity of the methanol- n-hexanol system as a function of concentration, and the coefficients of thermal diffusivity and thermal activity are calculated at high pressures.     

Metrological Characteristics of K-1 and K-3 Reference Benzoic Acids

A principle is presented for reproducing the unit of combustion energy, the joule, on the GÉT 16-96 State Primary Standard, which is based on using high-purity benzoic acid grade K-1. Metrological characteristics are given for various types of benzoic acid produced in various countries and used in combustion calorimetry. A comparison is made of the combustion energies for Russian K-3 benzoic acid and American 39i, which have been obtained with a GÉT 16-96.     

Relationship of dissolution rate in anionic polymeric solutions to viscosity

The influence of viscosity on the dissolution rate of m-acetotoluidide in aqueous solutions of acacia, gelatin type B, sodium carboxymethylcellulose, sodium alginate and xanthan gum was investigated. The viscosity was measured by a rotational viscometer. The dissolution rates decreased as the viscosities of solutions of anionic polymers increased. The curves representing the relationship of dissolution rate and viscosity varied for each polymeric solution depending on the structural characteristics of the polymer.     

Dissolution Characteristics of Benzoic Acid and Salicylic Acid Mixtures in Reactive Media

Abstract

The dissolution rates of mixtures of the two acids, benzoic acid and salicylic acid were determined in a phosphate buffered medium. Dissolution properties from compressed discs under sink conditions were essentially linear. Plots of dissolution rate versus compact composition deviated from the two component models for both non-interacting and interacting components. Dissolution rates, particularly for benzoic acid at intermediate weight fractions, were lower than predicted by the theory for two non-interacting components. These lower than expected rates were explained in terms of the physicochemical changes occurring in the microenvironment at the solid liquid interface.     

Transient diffusion through a porous plate between two compartments

Abstract

A general model describing transient diffusion through a porous or perforated plate between two compartments of changing concentrations is proposed. The equations derived from this model can be used to evaluate the effective diffusivity of a diffusing species in a porous material and the molecular diffusivity in a liquid phase. Several charts plotted from solutions to these equations are also presented for determination of diffusivity.     

Experimental verification of localized defect states in Ga-Ge-Se nano colloidal solutions

Linear optical studies on Ga₉Ge₂₇Se₆₄ nanocolloidal solutions were carried out. Evidence for the existence of defect states in these nanoclusters are obtained from absorption spectra, and its occurrence is emphasized by analyzing the fluorescence and thermal diffusivity studies. An intermediate peak in the band tail of the absorption spectrum is observed at high concentration, and it is interpreted as the absorption due to localized defect states. Fluorescence emission corresponding to this peak confirms the same. The thermal diffusivity studies show that nanocolloidal solutions with less solute concentration have high thermal diffusivity. This indicates the existence of high defect states density which increases with the increase in cluster size, leads to scattering of phonons from the defect centers and in turn results in lowering of thermal diffusivity.     

Diffusion in metallic glasses

Rutherfordα-particles backscattering technique was employed for measurements of diffusion rates in metallic glasses. Effects of relaxation, crystallization and plastic deformation on diffusion rates were also investigated. It has been observed that the diffusion rates of a metallic solute are of the same orders of magnitude in both metal-metal and metal-metalloid glasses. A higher diffusivity is likely if there is a large difference between melting points of the solute and matrix. Relaxation has no effect on diffusion, however, diffusivity increases on crystallization. An increase in diffusivity is also observed on plastic deformation of metallic glass.