Viscoelasticity of polydimethylsiloxane at the sol-gel threshold: structural effects

International audienceFive model polydimethylsiloxane (PDMS) networks were obtained by hydrosilation of a difunctional vinyl-terminated PDMS prepolymer with a SiH containing crosslinker. Viscoelastic experiments were performed in order to study the influence of molecular parameters on the dynamic properties at the sol-gel threshold. Critical parameters were determined close to and above the sol-gel threshold. The results obtained suggest that the critical exponents depend on the chemical structure of the incipient networks

Octadecylphosphonic acid self-assembled molayers as lubricant coatings stable in alkaline media

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Structural effects on the viscoelasticity of polydimethylsiloxane networks close to the sol-gel threshold

International audiencePolydimethylsiloxane (PDMS) networks were obtained by hydrosilation of a difunctional vinyl-terminated PDMS prepolymer with three crosslinkers of different functionality and molecular weight. These samples were studied using dynamic viscoelastic experiments as a function of time and frequency. Critical parameters were determined close to and ahove the sol-gel threshold. Rheological master curves could be built for the three PDMS networks above the gel point. The results obtained suggest that the critical exponents are not universal and depend on the chemical structure of the incipient networks

Advanced solid state NMR techniques for the investigation of the organic-mineral interfaces in biomaterials:2009 MRS Fall Meeting

High resolution solid state NMR experiments were carried out on several compounds, to see how this technique can now be used to investigate in detail the surface structure of different biomaterials. First, because the surface of titanium implants can be functionalized by phosphonic acids, for instance to prevent bacterial adhesion, 17O NMR experiments were performed on model TiO2 surfaces functionalized by 17O enriched phosphonic acids, to look at the mode of grafting of these coupling agents. Results bring clear evidence of the formation of Ti-O-P bridges and of the presence of residual P=O and P-OH groups. Second, given that calcium phosphates are widely present in biological hard tissues and synthetic biomaterials, 43Ca correlation experiments were performed on Ca enriched materials (hydroxyapatite and calcium benzoate), to see how the proximities between this nucleus and neighbouring atoms can be analyzed. Results show that both Ca...C and Ca...H proximities can be evidenced, and could thus help elucidate interface structures. All in all, these studies should pave the way to future investigations of biomaterials, and in particular of the structure of organic-inorganic interfaces. © 2010 Materials Research Society

Boronate ligands in materials: Determining their local environment by using a combination of IR/solid-state NMR spectroscopies and DFT calculations

Boronic acids (R-B(OH)2) are a family of molecules that have found a large number of applications in materials science. In contrast, boronate anions (R-B(OH)3 -) have hardly been used so far for the preparation of novel materials. Here, a new crystalline phase involving a boronate ligand is described, Ca[C4H9-B(OH) 3]2, which is then used as a basis for the establishment of the spectroscopic signatures of boronates in the solid state. The phase was characterized by IR and multinuclear solid-state NMR spectroscopy ( 1H, 13C, 11B and 43Ca), and then modeled by periodic DFT calculations. Anharmonic OH vibration frequencies were calculated as well as NMR parameters (by using the Gauge Including Projector Augmented Wave - GIPAW - method). These data allow relationships between the geometry around the OH groups in boronates and the IR and 1HNMR spectroscopic data to be established, which will be key to the future interpretation of the spectra of more complex organic-inorganic materials containing boronate building blocks. Boronate ligands in materials: A combined experimental/computational approach is used to define the IR and NMR spectroscopic signatures of boronate ligands in the solid state. OH stretching frequencies and 1H chemical shifts can now be related to the local environments around the OH groups (see figure). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim