Rheological Study of Chain Dynamics in Dilute Binary Polymer Mixtures

Abstract

Recent progress toward a more realistic understanding of chain dynamics in entangled binary mixtures has prompted us to examine in detail the nature of probe chain dynamics in binary mixtures in the dilute limit. We have carried out theoretical analyses to determine the solution rheological signatures of various types of chain dynamics and subsequently performed rheological measurements on a number of binary mixtures. We found in general agreement with the theoretical predictions that there are indeed several interesting regions including the familiar Zimm solution behavior, the Rouse-like solution behavior for both nonentangled and entangled matrices, and a Stokes-sphere dynamics involving a probe chain in a well-entangled "solvent". These experimental results reveal a high level of interplay between the probe and matrix chain lengths that dictates the actual probe chain dynamics. For example, a longer matrix chain is more effective in screening both excluded volume and hydrodynamic interactions and in delaying the onset of the nonlinear concentration dependence of the zero-shear solution viscosity.

A Biodegradable and Cross-Linkable Multiblock Copolymer Consisting of Poly(propylene fumarate) and Poly(ε-caprolactone): Synthesis, Characterization, and Physical Properties

“…Similar to many other polymers, a stronger exponent 2/3 was found in the frequency dependence of G ‘ and G ‘ ‘, showing departure from the estimate G ‘, G ∝ ω 1/2 based on the Rouse model . The crossover frequency for entangled polymer systems can be used as the reciprocal of the longest relaxation time .…”

“…The crossover frequency for entangled polymer systems can be used as the reciprocal of the longest relaxation time . It is apparent in Figure that the relaxation times decrease dramatically as much as 4−5 decades through changing chain friction coefficient and flexibility after introducing PCL segments into PPF backbone, despite the copolymer molecular weight is higher than that of PPF7hr.…”

“…For unentangled and entangled polymers, it is well-known that the molecular weight dependence for melt viscosity can be described as η 0 ∝ M 1.0 using the Rouse model and η 0 ∝ M 3.0 using the reptation model. ,,, Since both Rouse model and reptation model are single-chain approaches, they have been modified to interpret the stronger molecular weight dependences in polymer melts. Specifically, isofriction correction using chain-end free volume theory is for unentangled systems while contour length fluctuations and constraint release for entangled systems. ,,, In addition, the role of chain statistics in unentangled systems has attracted much attention recently .…”

“…For unentangled and entangled polymers, it is well-known that the molecular weight dependence for melt viscosity can be described as η 0 ∝ M 1.0 using the Rouse model and η 0 ∝ M 3.0 using the reptation model. ,,, Since both Rouse model and reptation model are single-chain approaches, they have been modified to interpret the stronger molecular weight dependences in polymer melts. Specifically, isofriction correction using chain-end free volume theory is for unentangled systems while contour length fluctuations and constraint release for entangled systems. ,,, In addition, the role of chain statistics in unentangled systems has attracted much attention recently . However, the origins and roles of these corrections in important parameters such as viscosity, relaxation time, plateau modulus, and diffusion coefficient are still in debate. 27b,c Figure shows the molecular weight dependence of the viscosity for six copolymers ( 1 , 2 , 4 − 7 ) with a similar PCL composition of ∼30% at various temperatures.…”

“…Specifically, isofriction correction using chain-end free volume theory is for unentangled systems while contour length fluctuations and constraint release for entangled systems. ,,, In addition, the role of chain statistics in unentangled systems has attracted much attention recently . However, the origins and roles of these corrections in important parameters such as viscosity, relaxation time, plateau modulus, and diffusion coefficient are still in debate. 27b,c Figure shows the molecular weight dependence of the viscosity for six copolymers ( 1 , 2 , 4 − 7 ) with a similar PCL composition of ∼30% at various temperatures. The linearity in Figure suggests the microstructure such as block length and distribution does not influence the macroscopical property η 0 strongly, as long as the block composition is fixed.…”