Molecular Relaxations

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Team members: A. Saiter (PR), L. Delbreilh (MCF)


The molecular mobility in the amorphous phases of polymers is investigated by Dielectric Relaxation Spectroscopy (DRS). This technique allows to significantly expand the range of response times conventionally explored by other dynamic techniques (e.g. Dynamic Mechanical Analysis, DMA) and provides a better comparison of the experimental data with the results obtained by numerical simulation. The high frequency experimental device is also equipped with a sealed and pressurized cell, a device which is essential to investigate bio-sourced or biodegradable materials that are very sensitive to humidity. The pressurized cell can be used to get precious information about the molecular mobility in systems that cannot be scanned at high temperatures due to a potential degradation or modification of the microstructure (e.g. PLA oligomers). From a fundamental point of view, such a pressurized system allows measuring the activation volume of the relaxation phenomena. On a whole, our research activities focus on understanding the physics of the glass transition in polymers. The objective is to measure any change in behavior (both in terms of frequency and temperature) as a function of the molecular weight, going from monomers (small molecules), to oligomers and finally to polymers, i.e. for molecular lengths which are way lower, comparable, or much larger than the correlation length typically observed in glasses.