Search results for "VOLUME"
showing 10 items of 1932 documents
A thermodynamic analysis on the coincidence of extrema conditions in the sorption equilibrium for ternary polymer systems
1993
Flory-Huggins theory of polymer solutions has been used to express the condition of extrema values in the total sorption, as well as the inversion point in the preferential adsorption parameters for termary polymer systems. Two approaches have been followed, the first considers the binary and ternary interaction parameters independent of polymer concentration and solvent composition. In the second one, this dependence has been introduced. Our attention is focused on the volume fraction of solvent mixture dependence of the above parameters, in order to confirm or not the coincidence between the extrema values and the inversion point. Several cosolvent and cononsolvent ternary polymer systems…
Prediction of maxima and minima in the curve of total sorption parameter in ternary polymer systems. Influence of ternary interaction parameter
1993
Flory-Huggins theory modified by Pouchly has been applied to predict maxima and minima in the curve of total sorption in ternary polymer systems formed by a polymer and two liquids. In this work, different diagrams based on experimental magnitudes easily obtained such as the difference in affinities of liquids, solvents and non solvents, and the solvent molar volume ratio. Total sorption parameter has been considered to be the decisive magnitude to define extrema conditions in both cosolvent and cononsolvent ternary polymer systems. The theoretical prediction is not altered by the inclusion of ternary interactions. Different examples of ternary systems dealing with vinyl polymers and polydi…
Entropy theory and glass transition: A test by Monte Carlo simulation
1997
This article reviews the results of a test of the Gibbs-DiMarzio theory by Monte Carlo Simulation. The simulation employed the bond-fluctuation model on a simple cubic lattice. This model incorporates two kinds of interactions: the excluded volume interaction among all monomers of the melt and an internal energy of the chains, which favors large bonds and makes the chains stiffen with decreasing temperature. The stiffening of the chains leads to an increase of their volume requirements, which competes with the packing constraints at low temperatures. This competition strongly slows down the structural relaxation of the melt and induces the glassy behavior. The model therefore takes into acc…
Structure and Yielding of Colloidal Silica Gels Varying the Range of Interparticle Interactions.
2016
The relationship between interaction range, structure, fluid-gel transition, and viscoelastic properties of silica dispersions at intermediate volume fraction, Φv ≈ 0.1 and in alkaline conditions, pH = 9 was investigated. For this purpose, rheological, physicochemical, and structural (synchrotron-SAXS) analyses were combined. The range of interaction and the aggregation state of the dispersions were tuned by adding either divalent counterions (Ca(2+)) or polycounterions (PDDA). With increasing calcium chloride concentration, a progressive aggregation was observed which precludes a fluid-gel transition at above 75 mM of calcium chloride. In this case, the aggregation mechanism is driven by s…
Self-diffusion in polymer solutions using the bond-fluctuation MC-algorithm
1991
Abstract A lattice Monte Carlo study of the self-diffusion of polymer chains in an athermal solution of equal chains is presented. The examined chain lengths, N (= 20–200), and volume fractions, φ (= 0.025-0.5), cover the range from dilute solution to concentrated solution, respectively. The dynamics show a gradual crossover from Rouse to reptation-like behaviour. Analysing the data according to a scaling theory and taking into account the density dependence of the microscopic length and time-scales, an almost perfect scaling of the self-diffusion coefficient is achieved. The high statistical accuracy of the data (103–104 chains per parameter combination) was obtainable by using a transpute…
Self-Diffusion of Small Molecules into Rubbery Polymers: A Lattice Free-Volume Theory
2010
In the framework of the Free Volume Theory, a new equation was derived for the evaluation of self-diffusion coefficients of small molecules in polymers above the mixture glass transition temperature. The derivation of the equation turned out to be straightforward once the equivalence between the free-volume and the unoccupied volume given by Thermodynamic Lattice Theories is assumed. A parameter evaluation scheme is proposed, which is substantially simpler compared to the conventional Vrentas-Duda approach, even without losing generality. The key assumption is discussed and its consistency is verified from a numerical viewpoint. A comparison with experimental solvent self-diffusion coeffici…
Analysis of gate freeze-off time in injection molding
2004
Gate solidification time is an important topic in injection molding technology, as it determines cycle time, which itself is an important issue in the economics of the production process. In this work, a study of the effect of both gate and cavity geometries on gate solidification time was conducted, using a commercial polymer, injection molded with constant holding pressure into a rectangular cavity. Three cavity lengths were used, and for each, two cavity thicknesses were adopted. Spe- cial dies containing different gates were assembled in the mold. Gate thickness was found to be the most important factor determining gate sealing time. However, the cavity geometry is also quite important.…
Der Verteilungsraum von physikalisch gelöstem Sauerstoff in wäßrigen Lösungen organischer Substanzen / The Distribution Space of Physically Dissolved…
1976
Abstract In order to evaluate the distribution of molecular oxygen in biological systems, the oxygen solubility (ml/ml atm) at 37 °C in aqueous solutions of thirty organic substances with different concentrations was measured by the classical Van Slyke principle. The oxygen solubility always (with the exception of hemoglobin) decreases exponentially with increasing concentration of the respective substance. In all cases this behavior is described highly significant by a simple empiric exponential function, when the substance concentration as well as the oxygen solubility of pure water is given. The influence of one substance on oxygen solubility contributes additively to the over-all solubi…
Understanding the kinetic solvent effects on the 1,3-dipolar cycloaddition of benzonitrile N-oxide: a DFT study
2011
JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, ISSN : 0894-3230, DOI : 10.1002/poc.1858, Issue : 7, Volume : 24, pp. 611 – 618, JUILLET 2011.
Ein Mikro-Atemstromventil für spontan atmende narkotisierte Kleintiere - A Respiratory Micro-Valve for Spontaneously Breathing Anaesthetized Small An…
1994
For the accurate functional analysis of the gas exchange in the lungs or evaluation of artificial oxygen carriers in spontaneously breathing anaesthetized small animals, we developed a new respiratory micro-valve. The body of the valve is made of aluminium, and the flaps are made of silicone rubber. The maximum flow rate in a rat measured with a pneumotachograph and the micro-valve was an average of 19.9 ml/s during inspiration, and 17.8 ml/s during expiration. The pressure measured in the tracheal tube was -0.85 during inspiration, and +0.39 cm H2O during expiration; the end-expiratory pressure in the tube was zero. In two experiments with anaesthetised rats lasting 4-5 hours, ventilation,…