Macromolecules in Constrained Environments

Les Houches summer school
Les Hoches, France
Some materials can see their macroscopic properties drastically influenced by the microscopic structure they exhibit. This is particularly the case when these materials are composed of geometrically constrained macromolecules. For example, in tire industry, the usage properties of silica filled elastomers are strongly dependent of the morphological details of the silica aggregates and of the ability to distribute them in the polymer matrix, which is known to entail large modification of the mechanical response of the system. It is believed that the specific behavior of this polymeric materials can be partially explained by looking at two characteristic sizes : the polymer radius of gyration (a couple of nanometers in the bulk) and the inter-particle distance (sometimes smaller than 1 nanometer). Geometrical confinement is therefore a key parameter. Similar confinement effect might be observed on complex fluid formulations containing polymer trapped at the nanoscale in complex porous media for example. This latest question is an important factor for enhancing oil recovery during oil extraction. Other examples may be found in the domain of polymer nano-composites, gels, or polymer thin films. If the detailed understanding of the microscopic origins of these effects does not raise a global agreement, it is usually admitted that many of these specificities arise from the presence of small characteristics distances in the system.

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