Bruno Bresson

New covalent bonded polymer–calcium silicate hydrate composites

New covalent bonded polymer–calcium silicate hydrate (C–S–H) composites were prepared. For this purpose, two sets of hydrosoluble copolymers, both containing trialkoxysilane (T-silane) and/or methyldialkoxysilane (D-silane) functions, were synthesized. The addition of these polymers during the synthesis of C–S–H by the sol–gel method allowed us to obtain hybrid materials. The influence of different synthesis parameters, such as the silane content and the nature of the silane functions grafted to the polymer backbone, was studied. Characterisation of the composite materials by thermogravimetry and elemental analysis showed that chemical interaction of polymers and C–S–H is due only to the presence of T-silane functions. 29Si CP MAS NMR analysis confirmed the existence of covalent linkages between the inorganic silicate chains of the C–S–H crystallites and the T-silane functions. The specific incorporation of these new classes of silane-modified polymers in C–S–H structure may be successfully used in the preparation of new polymer–cement composites with reinforced mechanical properties.

Hydration of tricalcium silicate (C3S) at high temperature and high pressure

Hydration products of tricalcium silicate (C3S) are the calcium silicate hydrates (C-S-H) and Portlandite. Silica fume, added to anhydrous cement in industrial formulations reacts with Portlandite and leads to C-S-H different from the previous one. C3S hydration with and without silica fume has been studied under high pressure (1000 bar) and high temperature (160°C) by numerous techniques (29Si and 1H NMR, XRD, Thermal analysis, SEM) for different hydration times. In these conditions, high temperature more stable crystalline phases are formed and their kinetics of formation is dependent on pressure. Besides, electrical conductivity measurement on hydrating cement under pressure have been carried out in order to evidence the great dependence of hydration kinetics with pressure. This study proposes a practical phase diagram which allows on a thermodynamical base to understand the change of equilibrium temperature with pressure. The kinetics of reaction has been studied and mechanisms of reaction proposed to explain the results.

Multiscale Surface-Attached Hydrogel Thin Films with Tailored Architecture

A facile route for the fabrication of surface-attached hydrogel thin films with well-controlled chemistry and tailored architecture on wide range of thickness from nanometers to micrometers is reported. The synthesis, which consists in cross-linking and grafting the preformed and ene-reactive polymer chains through thiol-ene click chemistry, has the main advantage of being well-controlled without the addition of initiators. As thiol-ene click reaction can be selectively activated by UV-irradiation (in addition to thermal heating), micropatterned hydrogel films are easily synthesized. The versatility of our approach is illustrated by the possibility to fabricate various chemical polymer networks, like stimuli-responsive hydrogels, on various solid substrates, such as silicon wafers, glass, and gold surfaces. Another attractive feature is the development of new complex hydrogel films with targeted architecture. The fabrication of various architectures for polymer films is demonstrated: multilayer hydrogel films in which single-networks are stacked one onto the other, interpenetrating networks films with mixture of two networks in the same layer, and nanocomposite hydrogel films where nanoparticles are stably trapped inside the mesh of the network. Thanks to its simplicity and its versatility this novel approach to surface-attached hydrogel films should have a strong impact in the area of polymer coatings.

Submicrometric Films of Surface-Attached Polymer Network with Temperature-Responsive Properties.

Temperature-responsive properties of surface-attached poly(N-isopropylacrylamide) (PNIPAM) network films with well-controlled chemistry are investigated. The synthesis consists of cross-linking and grafting preformed ene-reactive polymer chains through thiol-ene click chemistry. The formation of surface-attached and cross-linked polymer films has the advantage of being well-controlled without any caution of no-oxygen atmosphere or addition of initiators. PNIPAM hydrogel films with same cross-link density are synthesized on a wide range of thickness, from nanometers to micrometers. The swelling-collapse transition with temperature is studied by using ellipsometry, neutron reflectivity, and atomic force microscopy as complementary surface-probing techniques. Sharp and high amplitude temperature-induced phase transition is observed for all submicrometric PNIPAM hydrogel films. For temperature above LCST, surface-attached PNIPAM hydrogels collapse similarly but without complete expulsion of water. For temperature below LCST, the swelling of PNIPAM hydrogels depends on the film thickness. It is shown that the swelling is strongly affected by the surface attachment for ultrathin films below ∼150 nm. For thicker films above 150 nm (to micrometers), surface-attached polymer networks with the same cross-link density swell equally. The density profile of the hydrogel films in the direction normal to the substrate is confronted with in-plane topography of the free surface. It results that the free interface width is much larger than the roughness of the hydrogel film, suggesting pendant chains at the free surface.

Anisotropic super-attenuation of capillary waves on driven glass interfaces

Metrological atomic force microscopy measurements are performed on the silica glass interfaces of photonic band-gap fibers and hollow capillaries. The freezing of attenuated out-of-equilibrium capillary waves during the drawing process is shown to result in a reduced surface roughness. The roughness attenuation with respect to the expected thermodynamical limit is determined to vary with the drawing stress following a power law. A striking anisotropic character of the height correlation is observed: glass surfaces thus retain a structural record of the direction of the flow to which the liquid was submitted.

Nondestructive measurement of the roughness of the inner surface of hollow core-photonic bandgap fibers

We present optical and atomic force microscopy measurements of the roughness of the core wall surface within a hollow core photonic bandgap fiber (HC-PBGF) over the [3×10-2  μm-1-30  μm-1] spatial frequency range. A recently developed immersion optical profilometry technique with picometer-scale sensitivity was used to measure the roughness of air-glass surfaces inside the fiber at unprecedentedly low spatial frequencies, which are known to have the highest impact on HC-PBGF scattering loss and, thus, determine their loss limit. Optical access to the inner surface of the core was obtained by the selective filling of the cladding holes with index matching liquid using techniques borrowed from micro-fluidics. Both measurement techniques reveal ultralow roughness levels exhibiting a 1/f spectral power density dependency characteristic of frozen surface capillary waves over a broad spatial frequency range. However, a deviation from this behavior at low spatial frequencies was observed for the first time, to the best of our knowledge.

Picometer-scale surface roughness measurements inside hollow glass fibres

A differential optical profilometry technique with picometre-range sensitivity is adapted to the non invasive measurement of the roughness inside hollow glass fibres by use of immersion objectives and index-matching liquid.

NMR Spectroscopy Contribution to the Study of Biomaterial Mineralisation

High resolution solid state NMR spectroscopy is a powerful tool for understanding bone structures, bone substitutes and implants. In particular it can be used to estimate osteoformation via bioceramic bone colonisation. Pathological calcification occurring in bioprosthetic heart valves and breast prostheses can be characterised.