Crossover expressions for the craze extension ratio of semiflexible polymer glasses

Kramer’s formulas for the craze extension ratio λ_craze and fracture stretch λ_frac accurately predict these quantities for flexible polymer glasses with entanglement length N_e much larger than their Flory characteristic ratio C_∞, but break down badly for maximally entangled glasses (MEGs) with N_e = C_∞ because they do not account for chain stretching at the Kuhn segment scale. Accounting for this stretching yields alternative expressions that accurately predict λ_craze and λ_frac in MEGs [J. D. Dietz, K. Nan and R. S. Hoy, Phys. Rev. Lett. 129, 127801 (2022)], but these expressions break down as N_e/C_∞ increases. In this talk, we will present crossover expressions that accurately predict λ_craze and λ_frac in flexible and semiflexible polymer glasses spanning the entire range of chain stiffnesses and N_e/C_∞ values for which the glasses’ parent melts remain isotropic. We will explain the physics underlying these expressions in terms of how Kuhn-segment scale stretching in craze fibrils gets progressively stronger as polymers get stiffer.