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Soft matter templating for meso-macroporous materials

Soft matter templating for meso-macroporous materials


 


1. J. Mater. Chem. 2012, 22 (40), 21540 - 21548
2. RSC Adv. 2011, 1(7), 1204-1206


Hierarchical porous materials combine unique properties of mesostructures, such as high surface area and controllable sized pores, with those of macropores providing high diffusion and throughput rates. Typical applications of these materials are separation, catalysis, sensing or tissue engineering. They have also potential applications as reservoirs in drug delivery systems or as inclusion cavities for macromolecules. There are a number of ways to fabricate hierarchical macro–mesostructured silica, most of them combining soft and hard-templating techniques, for example by using small molecules, surfactants or polymers with hard colloidal spheres such as polystyrene (PS), poly- (methyl methacrylate) (PMMA) latexes or silica spheres, but also starch gels, polyacrylamide-based hydrogels, aerogels, polyurethane foams or wood tissue. Hierarchically porous materials have also been prepared without the use of hard templates, either based on in situ formed polymeric particles, bigels or emulsion droplets, to cite some of them.


One of our recent approach to design hierarchically porous silica consists in using solid lipid nanoparticles (SLN) as a novel soft template, that can lead to sub-micrometer macropores. Moreover, these nanoparticles are promising drug carriers for both hydrophilic or hydrophobic species. Therefore, combining inorganic silica matter with solid lipid nanoparticles, SLN, appears to be a straightforward approach for the development of novel hybrid organic–inorganic biocompatible materials with high potential applications in drug delivery and food chemistry.


Our pioneering work show that solid lipid nanoparticles (SLN) stabilized by nonionic polysorbate or block copolymer surfactants can lead to hierarchical meso–macroporous silica through a co-templated approach combining a cooperative templating mechanism (CTM) with micelles and spherical soft matter particles imprinting. Depending on the reaction conditions, the morphology of the final material can be tuned to capsules or to block matter. The size of the mesopores is strongly dependent on the nature of the surfactant in excess : 3 nm (Tween 20), 5 nm (Tween 40) or 9 nm (Pluronic ! P123), whereas the size of the macropores depends only on the size of SLN (250 ± 150 nm). The macroporous texture was clearly evidenced by TEM. The organization degree of the silica wall depends on the surfactant : only wormlike mesoporous capsules were obtained with Tween 20, and hexagonally ordered microdomains embedded in wormlike mesoporous silica capsules were obtained with Tween 40. Hexagonally ordered silica with circularly ordered mesoporosity could be achieved with Pluronic block copolymer P123.