Chemical modification of PDMS surface without impacting the viscoelasticity: Model systems for a better understanding of elastomer/elastomer adhesion and friction

The influence of both viscoelastic and interfacial parameters on the surface properties of elastomers is difficult to study. Here, we describe a simple route to achieve surface modification of PDMS without impacting the viscoelastic properties of the bulk. PEG modified PDMS surfaces were synthesized by two step surface modification based on hydrosilylation. The covalent grafting of PEG on the surface has been evidenced by AFM and ATR-FTIR, and its effect on the hydrophilicity characterized by static and dynamic contact angle. The static water contact angle of the PEG-modified PDMS decreases from 110° (for unmodified PDMS) to 65°. Dynamic contact angles also show a significant decrease in both advancing and receding contact angles, along with a significant increase in the contact angle hysteresis, which can be related to an increase in the surface energy as estimated by JKR measurements. The viscoelastic properties of modified PDMS are found to be quantitatively comparable to those of the unmodified PDMS. This simple method is an efficient way to prepare model materials which can be used to get a better understanding of the exact contribution of the surface chemistry on surface properties of elastomers.