Molecular Insights into the Interfacial Adhesion and Chain Adsorption of Silicone Polymers via Nanoindentation

Silicone-based polymers, particularly polydimethylsiloxane (PDMS), are esteemed for their exceptional thermal stability, hydrophobicity, and biocompatibility. This study leverages atomistically informed coarse-grained molecular dynamics (CG-MD) simulations to explore the interfacial adhesive characteristics of PDMS films subjected to nanoindentation, with a focus on the influences of interfacial interaction strength between nanoindenter and polymer chains, temperature, and cross-link density, interpreted through the classic Johnson-Kendall-Roberts (JKR) model. Our findings reveal that increasing the interfacial interaction strength significantly enhances adhesion, necessitating a greater energy for separation. Notably, beyond a certain threshold, the adhesion exhibits a plateau, as quantified by the apparent critical energy release rate, <i>G</i> _c. This saturation in <i>G</i> _c can be attributed to chain adsorption on the indenter tip. Such an interfacial adsorption phenomenon becomes more pronounced at elevated temperatures along with a concomitant decrease in <i>G</i> _c, due to enhanced chain mobility. Additionally, increasing cross-link density of the PDMS network reduces chain adsorption during indentation, thereby resulting in a higher apparent <i>G</i> _c. Our simulation results, confirmed by the experimental Atomic Force Microscopy (AFM) measurements, offer valuable insights into interfacial behavior of silicone-based polymers, highlighting the intricate interplay among interaction strength, temperature, and cross-link density in quantifying adhesive properties of PDMS films.