Air-Liquid Foams, Concentrated Direct Emulsion and Soft Chemistry Toward Hierarchically Organized Porous Silica Monolith
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Air-Liquid Foams, Concentrated Direct Emulsion and Soft Chemistry Toward Hierarchically Organized Porous Silica Monoliths F. Carn1, A. Colin2, M.-F. Achard1 and R. Backov1,* 1 Centre de Recherche Paul Pascal CNRS UPR 8641, 115 Ave Albert Schweitzer, 33600 Pessac, France ; 2 Laboratoire du Futur, UMR CNRS-Rhodia FRE2771, IECB, 2 rue Robert Escarpit, 33607 Pessac, France. [email protected] ABSTRACT Hierarchically organized matter appears today a strong and highly competitive field of research mainly induced by the wide scope of applications expected. In this context, chemistry of shapes appears as a strong interdisciplinary field of research combining soft chemistry and soft matter. Hierarchical inorganic porous monoliths can be obtained using either air-liquid foams or biliquid foams as macroscopic patterns while lyotropic mesophases are employed to promote porosity at the mesoscale. By controlling the air-liquid foam’s water liquid fraction or the emulsions oil fraction we can design the inorganic porous texture at the macroscale (i.e. cell sizes and shapes as well as the Plateau borders thickness). Those stategies lead to the formation of materials with characteristics that resemble aerogels. INTRODUCTION Metastable thermodynamic systems such as air-liquid [1] or biliquid [2] foams are of strong interest toward obtaining organized solid-state structures at the macroscopic length scale. To previous macroscopic patterns we can maintain micellar organization at the mesoscale leading thus to hierarchically organized architectures. Other routes enable to reach complex textures are based on either preformed nanoscopic patterns [3] or micro-organism [4]. The overall strategies are strongly related to a growing field called the “chemistry of shapes”[5]. In the specific issue where metastable thermodynamic systems are used as macroscopic patterns, disorganized macroporous inorganic foams have been generated using either an effervescence method [6] or a strong stirring process [7]. Recently our group has developed new processes to obtain macrocellular silica monoliths with a high degree of control over both cell sizes and morphologies [1], that we extended to other oxides like TiO2 [8] and V2O5 [9]. This first route uses a sol-gel foaming process where the foam’s water volumic fraction is controlled when performing the sol-gel chemistry. Concerning inorganic monoliths reached upon a more static method that combines biliquid foams and lyotropic mesophases, we played with the oil volumic fraction to tune the average macroscopic void space diameters while maintaining vermicular organization at the mesoscale thus obtaining new inorganic poly-HIPE scaffolds. EXPERIMENTAL DETAILS Tetraetoxyorthosilane (TEOS) and tretradecyltrimethylammonium bromide 98% (TTAB) were purchased from Fluka, HCl 37% and dodecane 99% were purchased from Prolabo, perfluorohexane was purchased from Acros-organics. Concentrated direct emulsion synthesis: The procedures are based on both micelles and direct emulsion templates. Typically 5
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