Measurement of the viscosity of irradiated silicone using a differential viscometer

High-energy electron (2.0 MV) and gamma irradiation (60Co) has been used to modify polymeric silicone fluids of initial viscosities in the range, 90–700 cSt. Doses of electron and gamma radiation were delivered at rates of 0.246 kGy s−1 and 15 kGy h−1, respectively, exposure times being adjusted to ensure energy deposition in the range 30–360 kGy. Measurements were made using a differential viscometer based on a Bose Institute design. In line with expectation, samples of greater initial molecular weight (and hence greater viscosity), were observed to be more susceptible to radiation induced cross-linking than those of lower molecular weight. The role of dose rate and oxygen diffusion in determining the extent of change is discussed.