Dr. Cédric Lorthioir is CNRS Research Director at Laboratoire de Chimie de la Matière Condensée de Paris, specializing in polymer chemistry, sustainable materials, and biopolymers.
The understanding of the macroscopic behavior of cross-linked elastomers, in particular mechanical, is based on the detailed description of the distribution of cross-linking density within these materials. However, the experimental approaches traditionally used – swelling measurements in good solvents or even from the elastic modulus to the rubber elasticity plateau – give access to the average value of the cross-link density, but not to its distribution. On the other hand, solid-state NMR uniquely allows for such a distribution to be determined, via measurements of the residual 1H-1H dipolar coupling associated with the elastically active chains of cross-linked structures.
During this seminar, the principle of these experiments (measurement of the rise in DQ coherences) will be briefly introduced. A first example, intended to illustrate this approach, will be proposed: it will involve studying the influence of micrometric inorganic fillers during the thermo-oxidative aging of filled elastomers. In a second step, the case of the study of multi-phase materials, such as immiscible mixtures of elastomers, will be addressed. Finally, in a final phase, the extension of these solid-state NMR experiments to polymer materials with topological constraints other than cross-linking nodes – chains grafted on a surface for example – will be addressed and illustrated by the study of block copolymers.