Effect of Molecular Weight, Polydispersity, and Monomer of Linear Homopolymer Melts on the Intrinsic Mechanical Nonlinearity 3Q0(ω) in MAOS

Abstract

Linear mono- and polydisperse homopolymer melts have been investigated with Fourier transformation rheology (FT rheology) to quantify their nonlinear behavior under oscillatory shear via mechanical higher harmonics, i.e., I3/1(ω,γ0). Master curves of the zero-strain nonlinearity, 3Q0(ω) ≡ limγ0→0 I3/1/γ02, have been created for these linear homopolymer melts, applying the time–temperature superposition (TTS) principle. The quantity 3Q0(ω) is examined for its dependence on molecular weight, molecular weight distribution, and monomer. The investigated nonlinear master curves of 3Q0(ω) for polymer melts with a polydispersity index (PDI) of about 1.07 or smaller display the expected scaling exponent of 3Q0(ω) ∝ ω2 at low frequencies until a maximum, 3Q0,max, is reached. This maximum 3Q0,max was found to be in the magnitude of the longest relaxation time τ0 and the value of 3Q0,max to be weakly dependent on molecular weight, or the number of entanglements Z, with 3Q0,max ∝ Z0.35. Within the measured experiment...