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Design of novel soft materials and understanding how soft networks break using mechano-fluorescence

Abstract : Elastic materials can deform reversibly by several times their initial size. Their low resistance to fracture is due to the presence of defects, which during deformation, lead to the still poorly understood catastrophic propagation of a crack. This thesis is organized around two axes: (i) the development of new elastomers designs for toughening, and (ii) the more fundamental study of fracture in more conventional elastomeric networks. Inspired by the structural reinforcement of multiple networks, we have developed two new ways of synthesizing reinforced elastomers: firstly, composites with soft and interpenetrable fillers of the same chemical nature as the matrix and secondly, films made from particles of interpenetrated networks synthesized by emulsion polymerization. We obtained composites with tunable strain-hardening according to the volume fraction of particles in the matrix. The double network particles obtained by emulsion polymerization could be functionalized chemically, which allowed their connection by covalent bonds during the drying process. In a second stage, we investigated the mechanisms of fracture of model elastomeric networks with a newly developed method allowing the mapping and quantification of network damage by fluorescence confocal microscopy. By varying the initial notch length in samples of the same polymer network and quantifying chain scission at the crack tip, we were first able to discuss the validity of the predictions of elastic fracture mechanics. Then, by varying the chain length in the polymer networks, we were able to investigate the effects of changing the network structure on chain scission at the crack tip and discuss the molecular model of Lake and Thomas. Finally, we observed in situ the necking process in multiple networks and quantified the local bond scission accompanying the stress transfer from the first to the second network. These new results will be useful for the development of new molecular models of fracture of elastic materials.
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Submitted on : Tuesday, March 15, 2022 - 2:07:09 PM
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  • HAL Id : tel-03609230, version 1

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Victoria Waltz. Design of novel soft materials and understanding how soft networks break using mechano-fluorescence. Material chemistry. Université Paris sciences et lettres, 2021. English. ⟨NNT : 2021UPSLS091⟩. ⟨tel-03609230⟩

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