Diffusivity and dissolution rate in polymeric solutions

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

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.     

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.     

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.     

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.     

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.     

The Wetting and Dissolution Rate of Phenobarbitone Powders

Abstract

The wetting of phenobarbitone powders by solutions of sodium lauryl sulphate has been measured. Large changes in contact angle and adhesion tension occur at low surfactant concentrations followed by more gradual changes at higher concentrations. The dissolution rates of phenobarbitone from capsules reflect these changes showing that initially, dissolution is penetration rate limited.     

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).     

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.     

Extraction of U(VI), Th(IV), and rare-earth elements from nitric acid solutions with phosphoryl-and carbonyl-containing podands

The distribution of HNO₃ and microamounts of nitrates of U(VI), Th(IV), La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y between aqueous solutions of HNO₃ and solutions of N,N′-dimethyl-N,N′-diphenyl-3-oxapentanediamide (I) and 1,3-bis(diphenylphosphinoyl)-2-oxapropane (II) in organic diluents was studied. The stoichiometry of the extractable complexes was determined, and the effect exerted by the extractant structure and by the organic diluent on the efficiency of recovery of rare-earth elements (REE) into the organic phase was examined. In nitric acid solutions, carbonyl-containing podand I surpasses in the extraction ability phosphoryl-containing podand II. The possibility of using a macroporous polymeric sorbent impregnated with compound I for recovering REE from nitric acid solutions was demonstrated. Original Russian Text A.N. Turanov, V.K. Karandashev, V.E. Baulin, 2007, published in Radiokhimiya, 2007, Vol. 49, No. 3, pp. 226–232.     

Influence of microstructure on hydrogen embrittlement behaviour of 2·25Cr–1 Mo steel

Abstract

The hydrogen embrittlement of Cr–Mo steel has been studied. The effects of tempering temperature on the hydrogen diffusivity and hydrogen assisted cracking, without external stress, are investigated. Hydrogen permeation and trapping, for the various microstructural conditions, were measured using electrochemical equipment. The microprecipitate distribution in the steel was observed using transmission electron microscopy. The steel, which was heat treated to give a variety of microstructures, was cathodically hydrogen charged and the critical microstructural sites for hydrogen induced cracking examined. Cracks initiated by the charging treatments were found to nucleate at MnS interfaces. Hydrogen diffusivity and trapping are strongly dependent on the tempering parameters.

MST/1947     

Studies Done in Single Rats,Simultaneously Comparing Disappearance Rates of Compounds from Different Regions of the Small Intestine

Abstract

Presented here are a) a simple procedure for measuring regional permeability differences of compounds in the small intestine of a single rat, and b) preliminary study to test the procedure utilizing seven different benzoic acids, e.g. benzoic acid, o-hydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid, p-hydroxybenzoic acid, m-hydroxybenzoic acid, 3,5-dinitrobenzoic acid, and 2,5-dihydroxybenzoic acid. Rates of disappearance (absorption) of these compounds were measured simultaneously in upper and lower segments of the small intestine using this variation of the in situ rat gut absorption study technique. Under the experimental conditions used, disappearance rate of a given compound was no different from upper or lower segment for any of the compounds except for p-hydroxybenzoic acid. The latter disappeared about three times faster from the upper than lower segment. Not only is this experimental procedure of utility in differentiating regional permeability within the intestine. It offers the option of testing the effect of an additive or other environmental change on compound permeability, while the other segment serves as a control.     

Behavior of plutonium in various oxidation states in aqueous solutions: II. Behavior of Pu(V) and Pu(III) at concentrations of 10<Superscript>−5</Superscript>–10<Superscript>−8</Superscript> M in solutions at pH ∼8

Pu(V) does not exist for a long time in solutions at pH ～8 and concentrations of 10^?5–10^?8 M because of disproportionation to polymeric Pu(IV) and Pu(VI), which form a common polymeric structure that subsequently does not significantly change. Plutonium(III) at its concentrations from 10^?5 to 10^?8 M in solutions at pH ～8 undergoes oxidation, transforming into polymeric Pu(IV). The data obtained can be useful for interpretation of the plutonium behavior under natural conditions.     

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.     

Surface modification of magnesium alloy AZ31 by hydrofluoric acid treatment and its effect on the corrosion behaviour

In the present study, the effect of hydrofluoric acid (HF) treatment on the surface composition and corrosion behaviour of the magnesium alloy AZ 31 was investigated. The HF treatment of the samples was performed with various concentrations and at different treatment times. The samples surfaces were analysed by Fourier transform infrared spectroscopy, optical emission spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. The results showed the formation of hydroxides, oxides and compounds of the general formula Mg(OH)_xF_2 − x on the samples surfaces, as well as variations on impurities concentrations. The process led to distinct surfaces, each having its specific corrosion resistance, which was evaluated by electrochemical impedance spectroscopy and potentio-dynamic polarization. The most improved corrosion protection was achieved using the concentrations of 14 and 20 mol L^− 1 and 24 h of treatment time, resulting in corrosion rates 20 times lower than those of untreated samples. These two solutions also resulted in an improved corrosion protection for further polymeric coatings, showing that this treatment is an excellent pre-treatment for corrosion protective layers on magnesium alloys.     

The importance of hemoglobin contents on viscosity of liposome encapsulated hemoglobin suspensions

Abstract

The viscosities of pig hemoglobin solutions and liposome encapsulated pig hemoglobin (LEH) suspensions were systematically measured as a function of shear rates, temperature, hematocrits of LEH suspensions, concentrations of hemoglobin solutions and hemoglobin contents in LEH suspensions. Newtonian flow behavior of hemoglobin solution is observed. Moreover, the viscosity values of the solutions linearly decrease as the solution warms from 4°C to 37°C, but non‐linearly increase with an increase in the concentration of hemoglobin in solutions. In contrast to hemoglobin solutions, LEH suspensions show non‐Newtonian flow behavior at all tested shear rates. The viscosity values of LEH suspensions non‐linearly decrease as the solution warms from 4°C to 37°C, but increase with an increase of hematocrit and hemoglobin content of solutions. The above mentioned non‐linear flow behavior of LEH suspensions is strongly dependent on the hemoglobin contents in suspensions. Moreover, LEH suspensions with hemoglobin contents of 7.2 g/dl is Theologically the most suitable suspensions for further applications.     

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.     

Fine-sized LiCoO2 particles prepared by spray pyrolysis from polymeric precursor solution

Fine-sized LiCoO₂ particles with high discharge capacities and good cycle properties were prepared by spray pyrolysis from a spray solution with citric acid and ethylene glycol. The precursor particles obtained from the spray solution with citric acid and ethylene glycol transformed into fine-sized LiCoO₂ particles with regular morphology after post-treatment at temperatures between 700 and 900 °C. The mean size and aggregation degree of the primary particles were affected by the concentrations of polymeric precursors added into spray solutions. The LiCoO₂ particles obtained from the spray solution without polymeric precursors had irregular and aggregated morphology. The discharge capacities of the LiCoO₂ particles changed from 132 to 151 mAh/g when the concentrations of the citric acid and ethylene glycol changed from 0 to 1 M. The particles prepared from the spray solution containing 0.3 M each of citric acid and ethylene glycol had the maximum discharge intensity.     

Gd2O3:Eu phosphor powders prepared using a size-controllable droplet generator

Gd₂O₃:Eu phosphor powders were prepared by a filter expansion aerosol generator (FEAG) process capable of changing the mean size of droplets. The change in the mean size of the Gd₂O₃:Eu phosphor powders according to the concentrations of polyethylene glycol added to spray solutions was caused by the difference in the mean size of the droplets produced via the FEAG process. The mean sizes of droplets produced by the FEAG process were affected by the surface tension and viscosity of the spray solutions. The mean sizes of the Gd₂O₃:Eu phosphor powders obtained from the spray solutions with the same concentration of metal salts changed from 1.5 to 4.2 μm according to the concentrations of polyethylene glycol and citric acid added to the spray solutions. The maximum photoluminescent intensity of the phosphor powders obtained from the spray solutions with polymeric precursors and boric acid flux was 144% of that of the phosphor powders obtained from the aqueous spray solutions without flux.     

The Influence of Polymeric Subcoats and Pellet Formulation on the Release of Chlorpheniramine Maleate from Enteric Coated Pellets

Abstract

The influences of aqueous polymeric subcoats and pellet composition on the release properties of a highly water-soluble drug, chlorpheniramine maleate (CPM), from enteric coated pellets were investigated. Three different aqueous polymeric subcoats, Eudragit® RD 100, Eudragit® RS 30D, and Opadry® AMB, were applied to 10% w/w CPM-loaded pellets that were then enteric coated with Eudragit® L 30D-55. Observed drug release from the coated pellets in acidic media correlated with water vapor transmission rates derived for the subcoat films. The influence of pellet composition on retarding the release of CPM from enteric coated pellets in 0.1 N HCl was investigated. The rate of drug release was greatest for pellets prepared with lactose, microcrystalline cellulose, or dibasic calcium phosphate compared with pellets formulated with citric acid and microcrystalline cellulose. Citric acid reduced the pellet micro-environmental pH, decreasing the amount of drug leakage in 0.1 N HCL during the first 2 hr of dissolution. Polymer flocculation was observed when CPM was added to the Eudragit L 30D-55 dispersion. An adsorption isotherm was generated for mixtures of CPM and the polymer and the data were found to fit the Freundlich model for adsorption. Adsorption of CPM to the polymer decreased with the addition of citric acid to the drug-polymer mixtures.