Effect of Chain Length Distribution on the Tearing Energy of Silicone Elastomers

Abstract

Abstract The tearing energies of two endlinked PDMS networks, one a monomodal distribution of chain lengths and the other a bimodal mixture of very short and rather long chains, at the same average molecular weight between crosslinks, were compared. The bimodal network exhibited higher tearing strengths than the monomodal network under the same experimental conditions. At threshold conditions, the bimodal network tearing energy was 70% higher than the threshold strength of the monomodal network. A rederivation of the Lake and Thomas theory for the threshold tearing strength which includes a bimodal probability distribution of chain lengths is shown to predict the observed behavior. The strength increase of these bimodal networks is attributed to the presence of the long chains which increases the energy required for fracture while maintaining the same number of chains crossing the fracture plane as in the monomodal network of the same crosslink density, by including a large number of short chains.