Investigating the relationship between the mechanical properties of plasma polymer-like thin films and their glass transition temperature

N. Vinx1, P. Damman2, P. Leclère3, B. Bresson4, C. Fretigny4, C. Poleunis5, A. Delcorte5, D. Cossement6, R. Snyders1,6, and D. Thiry1

1 Chimie des Interactions Plasma-Surface (ChIPS), University of Mons
Interface et Fluides Complexes (Influx), University of Mons
3 Laboratory for Chemistry of Novel Materials (CMN), University of Mons
4 Sciences et Ingénierie de la Matière Molle (SIMM), ESPCI
5 Institute of Condensed Matter and Nanosciences (IMCN), Université catholique de Louvain
6 Materia Nova Research Center, Parc Initialis, Mons
contact e-mail :

Plasma polymerization has become a well-established technique for the synthesis of solid organic thin films referred as plasma polymer films (PPF). Nowadays, despite a highly complex growth mechanism, it is possible to finely control the chemical composition of the PPF by a clever choice of the process parameters. On the other hand, tailoring their mechanical properties, which is a key requirement for their use is specific applications,[1] appears much more challenging. In this context, this work aims at developing an innovative way to easily tune the PPF mechanical properties, namely by externally regulating the substrate temperature (Ts) during the thin films synthesis. As a case study, propanethiol is used as a precursor.

By means of state-of-the-art AFM characterization-based techniques including Peak Force Quantitative Nanomechanical Mapping (PFQNM), nano Dynamic Mechanical Analysis (nDMA) and “scratch” experiments, it has been demonstrated that the PPF mechanical behaviour dramatically evolves from a high viscous liquid (i.e. viscosity ~ 106 Pa.s), to a viscoelastic solid (loss modulus ~ 1.17 GPa, storage modulus ~ 1.61 GPa) and finally to an elastic solid (loss modulus ~ 1.95 GPa, storage modulus ~ 8.51 GPa) when increasing Ts from 10 to 45°C. This behaviour is ascribed to an increase in the surface glass transition temperature of the polymeric network. The latter has been correlated with the chemical composition through the presence of unbounded molecules acting as plasticizers and the cross-linking density of the layers.

Finally, this knowledge previously acquired is exploited for the fabrication of nanopatterns by generating surface instabilities in propanethiol PPF/Al bilayer system.[2]

[1] de Oliveira, J. C., Airoudj, A., Kunemann, P., Bally-Le Gall, F. and Roucoules, V., SN Applied Sciences, 2021, 3, 1-15.
[2] Thiry, D., Vinx, N., Aparicio, F. J., Tessier, P. Y., Moerman, D., Leclère, P., Godfroid, T., Desprez, S. and Snyders, R., Plasma Processes and Polymers, 2020, 17, 2000119.