Viscoelastic properties of novel silicon carbodiimide gels

A novel non-oxide sol-gel system based on the reaction of bis(trimethylsily l)carbodiimide with methyltrichlorosilanes has been examined quantitatively with regard to its viscoelastic properties. The chemistry and phenomenolog y 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 dynam ic moduli G' and G " have also been measured versus strain amplitude and sh ear 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.