Projet ANR-06-BLAN-0097 – TSANET : TAILORED TRANSIENT SELF-ASSEMBLED NETWORKS
Programme : Programme blanc (BLANC) 2006
Année de financement : 2006
Coordinateur du projet : CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE LANGUEDOC-ROUSSILLON (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE LANGUEDOC-ROUSSILLON)
Partenaires : Centre national de la recherche scientifique; Centre national de la recherche scientifique
Montant : 270000.0 euros
Date de début : 2006
Durée : 36 mois
Résumé : Transient self-assembled networks (SANET) constitute a class of complex materials spontaneously forming reversible equilibrium 3-D networks which are transiently capable of transmitting elastic forces over macroscopic distances. This feature is at the origin of their spectacular viscoelasticity and extremely non-linear rheology at high shear rate that need to be elucidated because of the huge implications of fundamental and industrial interests. Among this class of viscoelastic materials, two very distinctive mechanical responses to high shear rates can be observed: the stress, as measured with a rheometer, is a smooth monotonic function of the shear rate, or the stress is an uneven, erratic function of it leading to a possible classification of these materials in two groups: (i) ductile fluids (smooth response with high shear, corresponding to a large amount of plastic deformation) versus (ii) brittle fluids (small or no plastic deformation before fracture occurs).  The scientific objective of the proposal is to obtain a fundamental understanding of the concept of ductility of soft self-assembled transient networks systems and more generally a fundamental understanding of the non linear rheological properties of these complex fluids. This requires designing well-defined self-assembled transient networks, described below for which we expect to control the more or less ductile character by modifying the nature and the distribution of vertices and bonds in the sample. For all tailored transient self-assembled networks on consideration, understanding the properties of soft matter both in the quiescent state as well as under flow conditions is needed. It is important to understand the strong coupling between magnitude and type of flow and structure, phase behaviour, and dynamics of responsive networks. Our methodological approach is an integrated approach taking advantage of the complementary nature of the partners exploiting the parallel development of experimental investigations of well defined model systems together with simulations and theory. Experiments using a variety of techniques will be made on the samples under quiescent, as well as flow conditions. Concurrently, theoretical and simulation studies will be performed on different length-scales to guide and be guided by the experiments. A multitude of experiments will be designed to obtain the maximum amount of information about the importance of individual structures and processes. Two different types of model transient networks will designed and studied : -(i) Entangled wormlike micelles of surfactants bridged by tailored hydrophobically endcapped hydrosoluble telechelic polymers (TBWM). This composite system will provide a very interesting experimental realisation of a network with freely sliding connexions. -(ii) Tailored bridged microemulsions (TBME) consisting of oil in water microemulsion droplets connected by hydrophobically endcapped hydrosoluble telechelic polymers, that form viscoelastic solutions at high enough droplets and polymer concentrations. We will study how the visocelastic properties of bridged microemulsions are modified when (a) a controlled polydispersity in the functionality of the network is introduced, (b) when a controlled polydispersity of the linker's size is introduced and (c) when loops configuration of the linkers are forbidden. Tailored telechelic polymers will be synthesized in our lab with specific length and hydrophobic anchors for the purpose. Phase diagrams of the systems and microstructural analysis, investigation of the dynamics in the equilibrium quiescent state, measurements of the linear and non linear viscoelastic properties of the systems using standard rheometers and finally, investigation of the ductile versus brittle character of the systems using strain geometries different from simple shear (extensionnal, Hele-Shaw) under time resolved optical observation (fast CCD camera) will be performed. In parallel, Monte Carlo an...