A short history of hybrid materials : a marriage of sand, clay and color

This second lecture (following on from the opening lecture) enabled us to better define the major classes of hybrid materials and to briefly describe the different strategies employed in the literature to build organo-mineral networks. Organic-inorganic hybrid materials can be defined as molecular-scale nanocomposites possessing at least one of their organic (biological) and inorganic components in a nanometric size range (a few Å to a few tens of nm). The properties of hybrid materials do not simply result from the sum of the individual contributions of their components, but also from the strong synergy created by a very extensive hybrid interface, which plays a major role in modulating a number of properties (optical, mechanical, separation, catalysis, stability to chemical and thermal stress, etc.). For this reason, the various hybrid materials have been classified into two main families, depending on the nature of the interface combining organic (biological) and inorganic components.

Class I corresponds to hybrid systems in which the organic and inorganic components interact via weak, Van der Waals, hydrogen or electrostatic bonds.

Class II corresponds to hybrid materials in which these components are linked by covalent or iono-covalent chemical bonds. Of course, many hybrid materials have both strong- and weak-bonded organo-mineral interfaces, but given the importance of the presence of strong chemical bonds in the end-use properties of the final hybrid material, this type of hybrid will also be classified in Class II.

Today, there are four main ways of developing hybrid materials: by inserting, intercalating or impregnating molecular or macromolecular organic components into a preformed lamellar or porous inorganic host network; by dispersing preformed inorganic nanocomponents in a polymer matrix; by forming the inorganic host network around the organic or biological component and vice versa; by simultaneously growing both organic and inorganic components. The degree of homogeneity of these materials is controlled by adjusting the growth kinetics of the different components, optimizing supramolecular interactions (Van der Waals, hydrogen or electrostatic bonds) or creating strong chemical bonds of a covalent or ionocovalent nature between the mineral and organic entities.

More than 10,000 publications and patents have been published on this subject (June 2010).

We felt it necessary to briefly describe the history of synthetic hybrid materials (see the Abstract illustrated in the following figure).

We have presented their evolution from their birth undoubtedly associated with chance, the driving force behind artists' creativity (prehistoric frescoes, ≈ 13,000 years old; Chinese porcelains, ≈ 5,000 years old then 1,500 years old ; mayan pigments, ≈ 1,200 years old), or to functional necessities (fabric bleaching or fading processes, ≈ 5,000 years old, Cypriot, Roman civilizations), until this early ^21st century in which their construction is tailor-made via legochemical, biomimetic or bioinspired approaches. In a more academic context, we have traced since the ^{mid-seventeenth} century the various stages and scientific discoveries that have enabled this field to become a truly original school of thought in materials science. Academic investment began with the formation of silica gels (J.B. Van Helmont, 1640 and J.J. Ebelman, 1844), followed by the birth of organic silicon chemistry (J.J. Berzelius, 1824) and the industrialization of silicones by Dow-Corning (1940). But it wasn't until the ^{mid-twentieth} century that academic institutions began to take an interest, initially in isolation, in mixed organic-mineral materials. The communities involved in research into clays, zeolites, glasses and ceramics using low-temperature synthesis (sol-gel methods), polymers and new hybrid molecular precursors all contributed to this theme. It wasn't until the early 1990s that the collective awareness and creation of this new school of thought really took place, fuelled by the organization of numerous highly transdisciplinary and multidisciplinary (chemistry, physics, biology) symposia and conferences. These fruitful exchanges not only gave rise to numerous collaborations, but also opened up new avenues of research, particularly those associated with biomimetic or bioinspired approaches leading to the development of functional hybrid materials with hierarchical structures.