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Transferts (imbibition, séchage) dans des matériaux bi-poreux multifonctionnels

Abstract : Some multi-scale building materials, like wood, hemp concrete or daub, exhibit high potential properties in terms of hygrometric diffusion (moisture expelling out of a house). In order to get a better insight into those properties, we investigate fluid transportation (soaking/drying) in doubly porous model systems based on polymeric materials envisioned by the double porogen templating approach. They are elaborated with controlled hydrophilicity and various large pore (LP) morphologies within the small pores matrix (SP): cubic or spherical, dispersed or connected by sharp-edged or smoother constrictions. We identify two categories of biporous structures leading to very diverging properties. Firstly, when dispersed large pores are included within the SP matrix, the liquid penetrates in the microporous matrix and the large pores absorb little to no water, and confining air inside them. Regardless the volume ratio of dispersed LP, the rising front is well described with different fluids by the classical Washburn theory inside the matrix only. On the other hand, when the large pores constitute a connected network, a competition between the imbibition within both porous networks (microporous matrix and macroporous network interacting with each other) determine the imbibition mechanism. If the rising of capillary front is fast in the macroporous network (smooth connexions between LP), it dominates the imbibition process, and the liquid can be drained by the smaller pore size close to it. In contrast, if the imbibition is slow in the macroporous network (sharp-edged constrictions between LP), then the microporous matrix controls the dynamic of soaking, and can speed it up with synergetic action highlighted by two distinctive rising fronts. The drying of those saturated biporous materials is investigated with 1H NMR relaxation and contraction monitoring. We demonstrate that drying mechanisms depends on the connectivity of large pores inside the microporous matrix too. Dispersed LP are homogeneously emptying first, resulting from a compression induced by the capillary pressure, whereas a connected LP network is emptying first too, but heterogeneously pore after pore. The drying rate is still constant in both cases during the majority of the desaturation
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Thibault Lerouge. Transferts (imbibition, séchage) dans des matériaux bi-poreux multifonctionnels. Matériaux. Université Paris-Est, 2019. Français. ⟨NNT : 2019PESC2081⟩. ⟨tel-02922137⟩

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