Viscoelastic properties of novel silicon carbodiimide gels

A novel non-oxide sol-gel system based on the reaction of bis(trimethylsilyl)carbodiimide with methyltrichlorosilanes has been examined quantitatively with regard to its viscoelastic properties. The chemistry and phenomenology of this process are completely analogous to the well-known oxide sol-gel process. The changes of the elastic modulus G' and the viscous modulus G " have been measured with low strain amplitude and constant frequency versus time. At the crossover point, i.e., G' = G ", the gel point is reached. The gelation time is independent of the oscillatory frequency omega. The dynamic moduli G' and G " have also been measured versus strain amplitude and shear stress amplitude. A relaxation exponent of n = 0.65, strength S = 0.25, and G'((end of reaction)) = 10(5) Pa.s have been determined.