Generalized model for dynamic percolation

We study the dynamics of a carrier, which performs a biased motion under the influence of an external field E, in an environment which is modeled by dynamic percolation and created by hard-core particles. The particles move randomly on a simple cubic lattice, constrained by hard-core exclusion, and they spontaneously annihilate and re-appear at some prescribed rates. Using decoupling of the third-order correlation functions into the product of the pairwise carrier-particle correlations we determine the density profiles of the "environment" particles, as seen from the stationary moving carrier, and calculate its terminal velocity, V_c, as the function of the applied field and other system parameters. We find that for sufficiently small driving forces the force exerted on the carrier by the "environment" particles shows a viscous-like behavior. An analog Stokes formula for such dynamic percolative environments and the corresponding friction coefficient are derived. We show that the density profile of the environment particles is strongly inhomogeneous: In front of the stationary moving carrier the density is higher than the average density, $\rho_s$, and approaches the average value as an exponential function of the distance from the carrier. Past the carrier the local density is lower than $\rho_s$ and the relaxation towards $\rho_s$ may proceed differently depending on whether the particles number is or is not explicitly conserved.Comment: Latex, 32 pages, 4 ps-figures, submitted to PR

Mass deacidification of papers and books. III : a study of a paper strenghtening and deacidification process with amino-alkyl-alkoxy-silanes

International audienc

Reaction modele de coamorcage en polymérisation cationique : analyses des produits de la réaction du TiCl4 avec le 2-isothiocyano-2,4,4-trimethylpentane

International audienc

Étude de la configuration du polysulfure de propylène par résonance magnétique nucléaire du carbone 13

La configuration d'échantillons de polysulfure de propylène cristallin et amorphe a été étudiée par RMN du carbone 13. L'attribution des pics a été faite grâce à des spectres de demi-découplage et par des mesures de temps de relaxation longitudinale des différents atomes de carbone. On observe une stéréosensibilité du carbone tertiaire. Par ailleurs, cette méthode d'analyse permet de détecter des irrégularités d'enchaînement qui apparaissent plus particulièrement pour les polymères préparés par voie cationique

Study of the interactions of organic sulfides with active species in the cationic polymerization of 1,3-pentadiene

Different alkyl sulfides (dimethylsulfide, ditertiobutylsulfide and diphenylsulfide) were investigated in the polymerization of 1,3-pentadiene initiated by aluminum trichloride in polar solvent in order to control the polymerization and to study the interaction between the electron donor and the active species. Thus, it was found that dimethylsulfide totally inhibited the polymerization, while thanks to its steric hindrance the polymerization occurred in the presence of ditertiobutylsulfide. However, for this electron donor, a transfer activity was evidenced at room temperature and at 0degreesC, which contributes to prevent the control of the polymerization. Diphenylsulfide stabilizes a little the active centers with nearly no transfer reaction. However in the studied experimental conditions, the stabilization was not sufficient to obtain a living polymerization

Templated polycondensation of aminopropyltrimethoxysilane on DNA

International audienceThe polycondensation of a silane derivative such asaminopropyltrimethoxysilane (ATMS) in the presence of DNA was investigated in an organicsolvent for the first time. Here, NMR observation showed that the hydrolysis step of ATMSbefore polycondensation was faster when the reaction was carried out in presence of doublestranded DNA (146 bp) in chloroform. In order to test the specificity of this enhancementeffect, the influence of the different components of DNA on ATMS hydrolysis and/orpolycondensation was then investigated using different bases, nucleosides and nucleotides.The results showed that the kinetics of ATMS hydrolysis was affected by the typeofnucleotide units used, the faster hydrolysis reaction rate being observed with moleculescontaining adenosine group, and that in the absence of water the amino group ofdeoxyadenosine units can react with ATMS methoxy groups