Seminar of Research Director Cédric Lorthioir - "Correlation between local structure of cross-linked polymers and mechanical behavior: solid NMR approach"
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.
Abstract:
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.
