Thermo-mechanical analysis of dental silicone polymers

Soft lining materials are used to replace the inner surface of a conventional complete denture, especially for weak elderly patients, with delicate health who cannot tolerate the hard acrylic denture base. Most of these patients have fragile supporting mucosa, excessive residual ridge resorption, particularly on the mandibular arch. The application of a soft liner to the mandibular denture allows absorbing impact forces during mastication and relieving oral mucosa. Actually, the silicone rubbers constitute the main family of commercialised soft lining materials. This study was conducted to understand the relationships between the mechanical properties and the physical structure of polysiloxanes. For this purpose, a series of polysiloxanes of various chemical compositions have been investigated. The evolution of their physical structure as a function of temperature has been followed by differential scanning calorimetry (DSC). In order to facilitate comparisons, the mechanical modulus has been analysed upon the same heating rate using dynamic mechanical analysis (DMA). Polysiloxanes actually commercialised as soft denture liners are three-dimensional networks: the flexibility of chains allows a crystalline organisation in an amorphous phase leading to the low value of the shear modulus. The dynamic mechanical analysis shows that they are used in the rubbery state. So, polysiloxanes have steady mechanical properties during physiological utilisation

INFLUENCE DE L'OXYDATION ET DE LA RUGOSITÉ SUR LES CARACTÉRISTIQUES RADIATIVES DES ACIERS INOXYDABLES

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Techniques de mesure des caractéristiques radiatives des matériaux opaques

This paper reviews the experimental techniques used in measuring the thermal radiation properties of opaque materials. After a survey of the different radiation parameters and the relations allowing reciprocal determination of some of them, a critical description of the main measurement techniques is made. The review extends from examining the methods of measuring spectral bidirectional reflectance, from which all other radiation parameters can be theoretically derived, to methods used for total hemispherical parameters. An emphasis is made on experimental error problems, specially those involved with polarization phenomena. Some means of avoiding these errors are suggested.Cet article est consacré à une revue synthétique des méthodes de mesure des propriétés radiatives des matériaux opaques. Après un rappel des différents paramètres radiatifs que l'on peut avoir à connaître et des relations permettant la détermination indirecte de certains d'entre eux, on donne une description critique et comparative de leurs principales techniques d'obtention. La démarche adoptée commence par l'examen des méthodes de mesure du paramètre radiatif le plus fin et peut-être le plus délicat à mesurer — la réflectivité bidirectionnelle monochromatique — et s'achève sur les paramètres les plus grossiers, à savoir les facteurs totaux hémisphériques, en passant par les différents facteurs intégrés sur l'espace ou la longueur d'onde. Un accent particulier est mis sur certaines causes d'erreur communes à la plupart des montages décrits, en particulier celles dues aux phénomènes de polarisation. Un moyen de s'en affranchir est indiqué

Similarities of the RBM and D Raman bands in double wall carbon nanotubes

Abstract We have examined several sets of heterogeneous double wall carbon nanotubes and analysed the frequency in a wide range of values. We have found that a statistical correlation exists between the D band intensity and the RBMs intensity. All the sample sets show a correlation of the RBM and D Raman intensity which is monotonic and non-linear using the 514nm laser excitation. Our results suggest that a similar mechanism is at the origin of the RBM and D bands. These results are corroborated by observations on carbon nanotubes embedded in a polymer matrix. We derive the phonon potential deformation for the D band and extend the excitation wavelength dependence of the D band to the UV. The intensity of the D band decreases with increasing hydrostatic pressure and fanishes at a pressure comparable to what has been observed earlier for the RBM and D* band