Understanding polymers degradation mechanisms in space environment

Position: 26-207 understanding polymers degradation mechanisms in space environment
## 26-207 understanding polymers degradation mechanisms in space environment
* Doctorat, 36 mois
* Temps plein
* Expérience : pas de préférence
* Maitrise, IEP, IUP, Bac+4
* Space environment and effects

Space is a hostile environment, both complex and dynamic. Synergistic effects of plasma, thermal cycling, sun radiation, charged particles, micrometeoroids... can cause severe damage on spacecraft materials and especially in Low Earth Orbit (LEO) with the additional impact of atomic oxygen as the major chemical constituent at this altitude. These degradations can affect seriously the performance of the spacecraft and its instruments and thus the duration of the mission.

To increase the knowledge of LEO environment and materials ageing, a first European experiment called EMA[1] (European Ageing Materials) has been developed by CNES with two main passengers:

- SESAME (Space Environment Study of Ageing of Mat Erials) with numerous materials, coatings and specific environmental sensors,- IR-Coaster (LISA/CNRS) with organic compounds.

EMA has now been exposed on ram direction outside the International Space Station since December 2024 with a retrieval planned for spring 2026.78 on-board CNES samples have been selected among thermoplastics, silicones, structural composites, adhesives, optical coatings, paints, thin films, adhesive tapes and contaminated samples.

The main objectives of the experiment are to study their behavior through the assessment of erosion rates, the evolution of their morphology and the characterization of their modified functional properties and compare data with on-ground results and previous data from other flight experiments. Additionally, adsorbents, optical witnesses, as well as a quartz crystal microbalance are exposed to collect potential molecular contaminants.

As observed on other flight missions such as MISSE[2] or MEDET[3], SESAME polymers should undergo significant changes since UV radiation has enough energy to break common molecular bonds and since the impact of atomic oxygen embrittles any organic material by oxidation and erosion. It is indeed well established that the degradation of the functional properties of polymeric materials subjected to environmental stresses is, in most cases, associated with modifications of their molecular structure.

These structural alterations typically involve a range of chemical reactions, including molecular rearrangements, oxidation processes leading to the formation of new functional groups (initiated by light, temperature, and/or radiation), crosslinking, and chain scission events. Moreover combined effects of UV radiation and atomic oxygen may contribute to complex degradation phenomena.

The proposed PhD project will be experimental. Thanks to pre and post flight characterization and any associated flight measurements, the missions of the doctoral student will be to better understand the physical and chemical changes of the exposed materials properties as well as the environmental effects on contaminated substrates, and suggest mechanisms to explain degradation, that may open new routes for  practice, a comparison of the material properties before and after exposure in LEO will enable the characterization of the modifications induced by environmental stresses.

In addition, laboratory irradiation experiments will be conducted using artificial weathering devices equipped with light sources at short wavelengths (254 nm).The chemical structure modifications of materials exposed both in LEO and under artificial laboratory conditions will be analyzed using a variety of techniques including infrared spectroscopy coupled with chemical treatments, micro-IR or ATR-IR spectroscopy and IR imaging in order to investigate the mechanisms and consequences of potential heterogeneous ageing.

Complementary analyses will be performed using UV–visible and fluorescence spectroscopy. Atomic Force Microscopy will be employed to assess surface property changes at the nanometric scale. In parallel, conventional analytical techniques commonly used in polymer characterization, such as Differential Scanning Calorimetry, Dynamic Mechanical Analysis and…