Diffusion and Rheology of Binary Polymer Mixtures

Abstract

This work studies the diffusion and rheological behavior of binary mixtures (of long and short chains) based on 1,4-polybutadiene over the full composition range as a function of both long and short chain lengths using pulse-gradient NMR spin echo and oscillatory shear measurements. The first set of rheological and diffusion measurements reveals that the terminal relaxation rate 1/τd and selfdiffusion coefficient Ds of the long chains both decrease systematically with increasing short chain length NS and with the weight fraction φ of the long chain in the mixtures. The second set of data indicates that the short chain's diffusion coefficient Ds decreases with increasing φ, leading to insightful comparison between the self-diffusion coefficient Ds at φ ) 0 and trace diffusion coefficient Dtr in the limit of φ ) 1.0: Dtr recovers the asymptotic molecular weight scaling of M -2.0 , whereas Ds scales nonideally as M -2.4 due to the considerable constraint release effect in the explored range of molecular weight. Third, short chains of molecular weight below Me are found to diffuse in entangled matrices of different chain length NL with a self-diffusion coefficient Ds that is independent of NL at all compositions.

Reptation and constraint release dynamics in bidisperse polymer melts

“…The diffusion coefficient D l /D mono against M s /M l scales with an exponent somewhat lower than −1. Similar observations have been made by Wang et al 27 for polybutadiene chains of comparable length with φ l = 20% and 10%. Both cases are added to Figure 2 as open symbols.…”

Linear Viscoelastic Behavior of Symmetric and Asymmetric Star Polymer Solutions

“…The observed scaling is nonetheless consistent with the experimentally observed exponents in the range of 3.4-4 from linear polymer solution studies using Θ-solvents or unentangled diluent chains of the same chemistry. [20][21][22][23] To understand the deviations between the measured and predicted exponents for the zero-shear viscosity of N250K solutions, it is useful to write the zero-shear viscosity as η 0 (φ p ) ) G N (φ p ) × τ rep (φ p ). Writing G N (φ p ) ∼ φ p 7/3 and τ rep (φ p ) ) τ e (φ p )[M/M e (φ p )] 3.4 ∼ τ e (φ p )φ p 68/15 , it is apparent that η 0 (φ p ) ) G N φ p 103/15 τ e (φ p ).…”

Analytical Rheology of Polymer Melts: State of the Art

“…Advances have been more forthcoming for polydisperse mixtures of LPs for three reasons, (i) there is a plethora of well-characterized experimental data [60,[206][207][208][209][210][211][212], (ii) rheological models have been built, tested, refined, and calibrated extensively [213], and (iii) it is possible to use approximate "double reptation-" type models [135,214], in lieu of the full tube model [142], which makes the mathematical model and its numerical solution more expedient.…”