Sol-gel and polymers for a wide variety of functional assemblies : the construction of " tailor-made" materials

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This lesson illustrated the scientific fusion that has taken place between the polymer community and that of researchers developing sol-gel processes based on soft inorganic chemistry. Historically, the two communities initially developed hybrid materials combining organic polymers and metal oxo-polycondensates resulting from condensation reactions of inorganic precursors, mainly metal alkoxides and organo-alkoxides. The polymer community, in search of new mineral fillers to improve the mechanical properties of composites, was quick to make use of soft chemistry, which enabled nanometric silica to be dispersed in situ and organo-mineral interfaces (the interface between reinforcing filler and polymer) to be better controlled, via hydrogen bond networks or covalent bonds using macromonomers functionalized with alkoxysilane groups. Cunningly, polymerists developed interpenetrating hybrid networks, giving rise to solid parts or shrink-free films, by polymerizing the solvent in which the inorganic polycondensation reaction takes place. The sol-gel community, for its part, developed the use of monomer-functionalized nanofillers (oxo-metallic clusters, nanoparticles) to synthesize hybrid nanocomposites starting from a perfectly defined mineral core (a filler). It has also been able to apply the phase separation processes familiar to polymerists, to synthesize bimodal porosity inorganic materials for high-performance chromatographic supports. But it wasn't until the mid-90s that the two communities began to collaborate more intensively. These collaborations have led to many fruitful discoveries, and to the development of complex, functional materials with highly interesting optical, mechanical and electrical properties.

Photonic crystals obtained by mineralizing ordered stacks of latex spheres, in contrast to electro-active opals obtained by impregnating ordered stacks of silica spheres with conducting polymers, are examples that highlight the rich collaborations between these two communities. In the second part of the lesson, we discussed more recent developments. These concern :

the use of organic polymers with amphiphilic blocks to generate dense or porous composite materials with regular but complex structures;
the coupling of gold nanoparticles and polymers to construct perfectly controlled hybrid analogues of block copolymers made of polymer-bonded metal nanorods. In these systems, the optical response of the gold can be modulated as a function of the inter-rod distance and hence the structure of the assembly. The latter can be adjusted by modulating the affinity between the polymer and the solvent to form long-chain structures, rings, bundles, spheres and so on;
the development of permselective membranes with a barrier effect;
the synthesis of hybrid mesoporous materials whose porosity is blocked by a "reversible gate" made of photo- and thermo-sensitive polymers, enabling optically controlled delivery of an active ingredient;
the development by electro-assisted extrusion of high-performance hybrid membranes for fuel cells, featuring new architectures similar to those of reinforced concrete.

The last part of this lesson gave us the opportunity to briefly present research which once again demonstrates that soft chemistry and polymer chemistry can be effectively married. In particular, the development of hybrid materials with hierarchical structures and the study of mineralization processes in the presence of biopolymers are highly topical subjects that will be developed in greater detail in future lectures.