Alain Lamure

Effect of polyphosphate binding on the chain dynamic of caseins: investigation by differential scanning calorimetry and thermally stimulated currents

Samples of caseins having different Ca contents as used in cheese processing were analysed by techniques using differential scanning calorimetry and thermally stimulated currents (TSC) before and after treatment with Na poly-phosphate, a food additive used in the manufacture of processed cheese. These techniques revealed structural changes induced by the salt, and the different types of water molecules associated with the protein are evident. This characterization is in agreement with results obtained by other techniques, particularly X-ray diffraction of proteins. Transmission electron microscopy of the same samples confirmed that the changes observed by TSC were associated with an unravelling of the protein.

Influence of moisture on the electrical properties of XLPE insulation

During their operating service, insulated power cables can be exposed to wet environment. The presence of moisture in cables surroundings may affect the properties of the used insulation material for instance, XLPE widely employed in MV and HV power cables insulation and therefore the reliability of the insulated cables. In order to examine the influence of wet aging conditions on the performances of XLPE insulated cables, samples (plates moulded from granules HFDE 4201-EC) of the same insulation material were exposed during 5600 hours to wet environment inside a cell simulating moisture. The XLPE material used in the present investigation is employed as insulation for medium voltage (MV) cables (18/30 kV). This work presents the results of the effect of aging under wet conditions on the electrical properties of XLPE. The goal of this paper was to investigate the eventual degradation of XLPE insulation under humidity effect by characterization techniques. For this purpose, measurements of dielectric losses factor, relative permittivity, volume resistivity and dielectric strength were performed.

Thermally stimulated current study of the molecular movements in bone

Thermally Stimulated Current (TSC) has been used for investigating the interface and interphase in a natural composite, bone. Young adult male femoral diaphysis has been studied at different stages of demineralization by EDTA. Analysis of the fine structure of complex TSC spectra has shown that in the early stages of demineralization, dielectric relaxations are due to the hydroxyl reorientations in the mineral apatite structure. After a certain stage of demineralization, the mineral response disappears and organic matrix mobility is observed. A dissociative buffer has been used to identify collagen relaxations. The contribution of the mineral-organic interface/interphase has been isolated.ZusammenfassungThermisch erregter Strom (TSC) wurde zur Untersuchung von Grenzflächen und Grenzphasen in der natürlichen Substanz Knochen verwendet. Mittels EDTA wurde die Femoraldiaphyse von jungen erwachsenen männlichen Individuen in verschiedenen Stadien der Demineralisierung untersucht. Eine Analyse der Feinstruktur von TSC-Spektren zeigte, daß in den frühen Stadien der Demineralisierung dielektrische Relaxationen in Verbindung mit der Hydroxyl-Reorientierung in der Apatitstrukur stehen. Nach einem gewissen Demineralisierungsstadium verschwindet die Mineral-Antwort und die Mobilität der organischen Matrix wird beobachtet. Zur Identifizierung von Kollagen-Relaxationen wurde ein dissoziativer Puffer eingesetzt. Der Beitrag von mineral-organischer Grenzfläche/Grenzphase wurde voneinander getrennt.

Study of SU-8 reliability in wet thermal ambient for application to polymer micro-optics on VCSELs

We present experimental data on the reliability of SU-8 polymer when used as a core material for the integration of microlenses on vertical-cavity surface-emitting lasers (VCSELs). The respective effects of a hot and humid environment on structural, mechanical and optical properties of this epoxy resist are investigated. High aspect-ratio SU-8 micropillars are found to keep a good surface morphology and a stable optical transmission, as well as a good adherence on the wafer. Thermal cycling is also studied to check material stability under electro-thermal actuation in SU-8 micro-opto-electro-mechanical system (MOEMS). These results are of great importance for the collective integration of low-cost SU-8-based passive or active microlens arrays onto VCSELs wafers for optical interconnects and optical sensing applications.

Effect of moisture on breakdown voltage of polyesterimide used in electrical machines

This paper deals with the influence of humidity on breakdown voltage of polyesterimide. The specimens were submitted to an hydrolytic aging, under 90% humidity and 30°C temperature, until 3000 h. The breakdown tests were executed under AC and DC voltage. A statistical analysis of the breakdown voltage data was carried out using Weibull model. The 90% confidence bounds were calculated and plotted. The study shows that breakdown voltage varies versus the aging time. Its increase is allotted to the crosslinking of the material structure. Whereas its decrease is ascribed to the plastificization of the polymer. The breakdown voltage under DC ramp is higher than that obtained under AC ramp. The DC breakdown voltage depends on the polarity.

Thermostimulated current study of the dynamic behaviour of a biocomposite: calcified tissue

Abstract Thermostimulated current (TSC) spectroscopy has been applied to the investigation of molecular mobility in human calcified tissue. A comparative study of extracts and residues, at various stages of demineralization, by gel permeation chromatography and TSC spectroscopy, has shown that collagen is not directly linked to apatite: the response of an organic-mineral complex interphase has been identified.

Role of interfaces on a natural composite bioelectret: bone

The aim of this study is the characterization of interfaces in calcified tissues. Thermally stimulated currents and gel permeation chromatography have been used for investigating extracts and residues from calf femoral diaphysis at various stages of demineralization. In the residues, evolution of molecular mobility shows that the organic-mineral linkage is ensured by several proteins. Collagen is not directly linked to apatite.<<ETX>>

Polarization phenomena on silicone

Practical experiments show that silicone adhesion on glass can be increased by eliminating the lowest molecular weight chains. The aim of this work is to precise the influence of short chain segments on silicone mobility. For this study, PolyDimethylSiloxane (PDMS) samples have been characterized by the Thermally Stimulated Current (TSC) spectrometry. In silicone, dielectric relaxations have two different origins: they are associated either with transitions or with polarization phenomena. At lower temperature, all the samples are characterized by the dielectric manifestation of the glass transition and, only after fractionating, with crystallization and melting phenomena. Around the room temperature, the polarization relaxation can be associated with adhesion mechanisms. Complementary dielectric, mechanical and thermal experiments have shown that these relaxation could be associated with surfacic polar group rotations around the Si-O and probably at the origin of silicone adhesive properties.

Ex-Vivo Study of Molecular Interfaces in Calcified Tissues

The aim of this work is the characterization of interfaces in calcified tissues. Thermally Stimulated Currents and Gel Permeation Chromatography have been used for investigating extracts and residues from calf femoral diaphysis, at various stages of demineralization. In residues, the evolution of molecular mobility shows that the organic-mineral linkage is insured by several proteins: Collagen is not directly linked to apatite.