Using thickness-shear mode quartz resonator for characterizing the viscoelastic properties of PDMS during cross-linking, from the liquid to the solid state and at different temperatures

Characterizing the effects of cross-linking level and kinetics on the mechanical properties of rubber, especially viscoelasticity, provides information of importance to better understand and predict final mechanical properties. Classically, the effects of cross-linking on the mechanical properties are investigated with a rheometer. Typical results give the evolution of elastic properties of rubber in the solid state with respect to time or cross-linking level. In the case where the rubber is initially in the liquid state, such as some silicone rubbers, this type of characterization is not suitable anymore. In this study, the Quartz Crystal Microbalance (QCM) principle has been used in order to characterize the viscoelastic properties (elastic and viscous moduli) of a silicone rubber during cross-linking, from the liquid (uncross-linked) to the solid (final cross-linked) state. The device consists in a Thickness-Shear Mode (TSM) resonator generating ultrasonic waves, which provides viscoelastic properties of a material in contact with its surface from an electrical impedance analysis. In contrast to other characterization tools, it makes possible the continuous and non-destructive characterization of viscoelastic properties from a small material volume, under 1mL. It has been used to characterize the evolution of the viscoelastic properties of a poly-dimethylsiloxane during cross-linking at three different temperatures: 25 degrees C, 50 degrees C and 80 degrees C. Results have shown that the final viscoelastic properties depend on the temperature during crosslinking. The higher the crosslinking temperature, the lower (higher) the final elastic (viscous) modulus at 25 degrees C. This is explained by the strong difference in the cross-linking kinetics obtained with the temperatures applied. (C) 2018 Elsevier B.V. All rights reserved.