Molecular simulation study of the heat capacity of metastable water between 100K and 300K

Molecular simulation study of the heat capacity of metastable water between 100K and 300K Molecular simulations have been used to study the heat capacity of metastable liquid water at low temperature adsorbed on a smooth surface. These calculations aim at modelling water properties measured by experiments performed on water films adsorbed on Vycor nanoporous silica at low temperature. In particular, the study focuses on the non-monotonous variation of the heat capacity around between 100 and 300 K

Polymetalates based organic-inorganic nanocomposites

New nanocomposites materials have been synthesized. They present electrochemical and photochromic properties. They are based on a hybrid organic-inorganic network, in which tungsten heteropolyoxometalates (PW12O40(3-), SiW12O40(4-), W10O32(4-), polymeric tungstate) are entrapped. High tungsten ratios could be reached and films or bulk materials have been obtained. The structure of these materials is described on the basis of multi-spectroscopic investigations (IR, EPR, NMR). Electrochemical redox reactions have been observed in thin films. Dark blue reversible coloration of the materials is obtained under UV irradiation. The photochromic mechanism has been investigated and shows the reversible formation of carbonyl group

Photochromic organic-inorganic nanocomposites as holograpahic storage media

This paper describes the properties of some new organic-inorganic photochromic layers. They are based on a hybrid organic-inorganic matrix in which tungsten heteropolyoxometallates (SiW12O404-, PW12O403-) are entrapped in a network obtained from the reaction of 3-glycidoxy-propyltrimethoxysilane. The high homogeneity of these materials on the nanoscale leads to transparent monoliths and layers of controlled thicknesses up to 40 µm. The optical properties of the blend are emphasised and the construction of amplitude gratings in the materials by two-wave-mixing experiments is described. The results of the optical experiments and the comparison with the theoretical background are used as a model for photochromic holographic storage processes

Dynamics of the sol-gel transition in organic-inorganic nanocomposites

Two different techniques have been used to follow the gelation of photochromic organic-inorganic nanocomposites. The variations of molecular and macromolecular motions in these complex systems have been analyzed. Photo-correlation spectroscopy probes the formation of the gel network. Forced Rayleigh scattering experiences the microstructure of the mixtures via the measurement of the translational diffusion coefficient of entrapped photoreactive targets. In the different mixtures, a drop of the network mobility could be observed around the sol to gel conversion, while the entrapped molecules do not experience the macroscopic transition

Competing coexisting phases in 2D water

International audienceThe properties of bulk water come from a delicate balance of interactions on length scales encompassing several orders of magnitudes: i) the Hydrogen Bond (HBond) at the molecular scale and ii) the extension of this HBond network up to the macroscopic level. Here, we address the physics of water when the three dimensional extension of the HBond network is frustrated, so that the water molecules are forced to organize in only two dimensions. We account for the large scale fluctuating HBond network by an analytical mean-field percolation model. This approach provides a coherent interpretation of the different events experimentally (calorimetry, neutron, NMR, near and far infra-red spectroscopies) detected in interfacial water at 160, 220 and 250 K. Starting from an amorphous state of water at low temperature, these transitions are respectively interpreted as the onset of creation of transient low density patches of 4-HBonded molecules at 160 K, the percolation of these domains at 220 K and finally the total invasion of the surface by them at 250 K. The source of this surprising behaviour in 2D is the frustration of the natural bulk tetrahedral local geometry and the underlying very significant increase in entropy of the interfacial water molecules

Enhancing in vitro biocompatibility and corrosion protection of organic-inorganic hybrid sol-gel films with nanocrystalline hydroxyapatite

Application of novel organic-inorganic hybrid sol-gel coatings containing dispersed hydroxyapatite (HAp) particles improves the biocompatibility, normal human osteoblast (NHOst) response in terms of osteoblast viability and adhesion of a Ti6Al4V alloy routinely used in medical implants. The incorporation of HAp particles additionally results in more effective barrier proprieties and improved corrosion protection of the Ti6Al4V alloy through higher degree of cross-linking in the organopolysiloxane matrix and enhanced film thickness

Vibrational analysis of d-PCL(530)/siloxane based hybrids doped with two lithium salts

Published online: 22 May 2013The present study has been focused on environmentally friendly sol-gel derived electrolytes based on a di-urethane cross-linked d-PCL(530)/siloxane network (where d represents di, PCL identifies the poly(ε–caprolactone) biopolymer and 530 is the average molecular weight in g.mol-1) doped with a wide range of concentration of lithium perchlorate (LiClO4) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Fourier Transform Infrared and Raman (FT-IR and FT-Raman, respectively) spectroscopies have been applied to evaluate the extent of ionic association. Characteristic bands of the PCL(530) segments, of the urethane cross-links and of the anions have been examined to gain insight into the cation/biopolymer, cation/anion and cation/cross-link interactions. In both electrolyte systems “free” ions and contact ions have been identified. The addition of salt modifies the hydrogen-bonded array of the host matrix, causing the destruction/formation of the urethane/urethane aggregates.Fundação para a Ciência e a Tecnologia (FCT

Geopolymer/PEG Hybrid Materials Synthesis and Investigation of the Polymer Influence on Microstructure and Mechanical Behavior

Geopolymers are aluminosilicate inorganic polymers, obtained from the alkali activation of powders containing SiO2+Al2O3>80wt%, mainly proposed as environmentally friendly building materials. In this work, metakaolin-based geopolymers have been prepared and a water-soluble polymer, polyethylene glycol (PEG), has been added in different percentages to obtain organic-inorganic hybrid geopolymers. The influence of both the polymer amount and aging time on the structure and the mechanical behavior of the materials were investigated. FTIR spectroscopy allowed us to follow the evolution of the aluminosilicate framework during the geopolymerization process. This analysis revealed that PEG leads to a network which is rich in Al-O-Si bonds and forms H-bonds with the inorganic phase. SEM microscope showed that the two phases are interpenetrated on micrometric scales. Traction and bending tests have been carried out on appropriate samples to investigate the mechanical behavior of the obtained hybrids, showing that both PEG content and aging time affect the material behavior