Singularities in hydrophobic recovery of plasma treated polydimethylsiloxane surfaces under non-contaminant atmosphere

• We examine the hydrophobic recovery of plasma treated PDMS surfaces.
• We find the occurrence of singularities under nitrogen for low aging temperatures.
• Theses singularities account for different population of relaxation processes.
• The faster concerns reorientation processes at the surface of the crosslinked layer.
• The slower concerns diffusion processes in the sub-surface region.

Herein, the hydrophobic recovery of argon plasma treated polydimethylsiloxane surfaces is explored. In contrast to previous works, environmental contamination is here taken into account. We find that diffusion and reorientation strongly dominate the hydrophobic recovery under high thermal activation (60 °C), no matter the surrounding environment during storage. However, at lower temperature (24 °C and below), we find that contamination plays a major role in lab atmosphere environment. By working at low temperature and under inert nitrogen atmosphere to slow down the diffusion and reorientation dynamics and to avoid contamination, we identify two different temperature-dependent regimes in the kinetics of the hydrophobic recovery. One is fast and involves exclusively relaxation processes occurring in the surface region. The second, much slower, concerns diffusion phenomena in the sub-surface region. Thereby, the specific impact of bulk diffusion and surface reorientation processes can be distinguished during aging by slowing down the surface dynamics and by eliminating all possible sources of contamination.