1,720,974 research outputs found
Combined extension and torsion of a swollen cylinder in unsteady conditions for the mechanical characterization of a hydrogel: An application of the continuum theory of mixtures
No full textDue to the growing technological interest on gels, there is a need for more and more accurate mechanical and thermodynamic experimental characterizations. To this aim, we have simulated the stress relaxation behavior of a cylindrical gel sample subjected to a finite combined extension and torsion. To account for the biphasic nature of the gel, we have used the continuum theory of mixtures in unsteady conditions, adopting a Flory-Rehner expression to describe the Helmholtz free energy of the gel. The results of the simulations showed a pronounced relaxation of the axial force along with a shallow relaxation of the torque: while the former effect is a direct consequence of the solvent outflow, the latter one is only an indirect consequence of solvent movement. Both properties can be conveniently used to evaluate the mechanical and diffusive characteristics of a gel with an ordinary rheometer. We have also performed a parametric study of the model to highlight the main influence of the material constants appearing in the constitutive equation. © 2012 Elsevier Ltd. All rights reserved
Application of the mixture theory to the unsteady elongation and torsion of a biphasic hydrogel
No full textMechanistic Understanding of Degradation in Bioerodible Polyanhydrides: Consequences for Drug Delivery
No full textMechanistic Understanding of Degradation in Bioerodible Polyanhydrides: Consequences for Drug Delivery
No full textGas sorption and transport in syndiotactic polystyrene with nanoporous crystalline phase.
No full textIn this contribution we analyze sorption and transport of several gases in semicryst. syndiotactic polystyrene with nanoporous cryst. d form. Investigation was performed on amorphous samples and on samples characterized by different degrees of crystallinity. Sorption isotherms of carbon dioxide, nitrogen and oxygen in the cryst. phase have been detd. starting from exptl. results obtained for semicryst. and amorphous samples. Corresponding isosteric heats of sorption were evaluated for the cryst. and amorphous phase. Permeation tests were also performed to gather information on mass transport properties of semicryst. samples, evaluating av. diffusivities of carbon dioxide and oxygen, in the limit of small concns. as function of degree of crystallinity
An Integrated Approach to Analyze Long-term Moisture Transport inHoneycomb-core Sandwich Panels
No full textA predictive model for the time evolution of moisture uptake within a honeycomb-core sandwich has been developed. The model takes into account the water diffusion into the skins as well as into the honeycomb part of the sandwich. Experimental evidence has been found of hydrolysis of the aramidic pulp of the
honeycomb, which has been consequently accounted for in the model through an irreversible reaction term. The relevant parameters of the model (diffusivities, solubilities, and aramidic hydrolysis kinetic constants), for each single component
making up the sandwich, have been experimentally evaluated at several temperatures and relative humidities. Predictions of the model successfully compare with experimentally determined water uptake kinetics into the whole sandwich
Effect of cyclodextrin incorporation into protein-loaded PLGA-based microspheres: the case of insulin/hydroxypropyl-beta-cyclodextrin complex.
No full textThe aim of this work was to clarify the mechanisms by which the co-encapsulation of cyclodextrins into insulin-loaded PLGA microspheres influences protein release rate. On the basis of our previous results, microspheres were prepared by spray-drying either a W/O emulsion or an acetic acid solution with or without HPbetaCD. In order to achieve a more complete characterization of the system, a spectrophotometric method, based on HPbetaCD complexation with phenolphthalein, was used to measure its loading in and release from the microspheres. Furthermore, in order to get an insight into insulin/HPbetaCD interactions within PLGA microspheres after production and during the release phase, the influence of HPbetaCD addition on the secondary structure of bovine insulin within dried and rehydrated microspheres was assessed. To this end, the most valuable and non-invasive method was considered Fourier transform infrared (FTIR) spectroscopy, which can provide, without altering the controlled release system, detailed information regarding protein conformation
Confocal Raman imaging, FTIR spectroscopy and kinetic modelling of the zinc oxide/stearic acid reaction in a vulcanizing rubber
No full textThe reaction of zinc oxide (ZnO) with stearic acid (StA) to form zinc stearate (ZnSt) has been investigated experimentally in a model matrix (unvulcanized styreneebutadiene rubber) by using confocal Raman microscopy and FTIR transmission spectroscopy. The heterogeneous nature of the reacting system has been confirmed. The Raman analysis has revealed the coreeshell structure of the product, which is formed via the gradual shrinkage of the ZnO core and the concurrent formation of a surrounding ZnSt shell of increasing thickness. FTIR spectroscopy has provided information about the molecular state of
aggregation of StA when dissolved in the rubber, as well as quantitative information on the reaction kinetics. The kinetic behaviour of the system has been interpreted using a semi-quantitative heterogeneous reaction model grounded on the Raman imaging results, which was able to catch the essential
features of the phenomenon and to simulate reliably the experimental conversion vs time data at three different temperatures
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