Rheological
responses during uniaxial extension of polymer melts
Project
description: The rheological study of polymer melts has been debated for
several decades, and plenty of problems, e.g., the origin of nonlinear behavior
upon deformation, remain to be solved. This project focuses on the non-linear
responses of Polyisoprene melts during uniaxial extension.
Responsibilities:
- Systematically studied and
summarized the factors controlling the different failure modes during uniaxial
extension of entangled polymer melts, which will guide and improve various
polymer processing procedures
- Made the first attempt to identify
the true difference in the nonlinear responses of entangled polymer melts and
polymer solutions upon uniaxial extension
- Pointed out the deficiency of current
rheology theory by Analyzed thermodynamic and viscoelastic behavior of polymer
melts.
Results: This
work has been presented at several conferences and provides a key clue for understanding the molecular deformation mechanism
of entangled polymers in fast flow.
Non-linear mechanical responses of polymer glasses
Project description: Polymer glasses has been an important but very tough aspect of polymer physics. In this project, a series experiments of mechanical responses of PC, PS and PMMA at temperatures well below Tg have been carried out.
Responsibilities:
- Systematically investigate the impact of melt processing on mechanical behavior of glassy polymers and apply it to precisely control of the mechanical responses of polymer glasses.
- Developed new understanding of polymer dynamics below the glass transition by studying stress relaxation behavior of polymer glasses
- For the first time summarized the factors that affect the brittle-ductile transition (BDT) of polymer glasses under compression
- Discovered and systematically studied the unexpected polymer-additives interactions that varies the mechanical responses of polymer glasses.
Results: This experimental studies result in several publications provide a unique way to improve the theoretical understanding of what controls the mechanical properties of polymer glasses.
Collaborative project: Elucidating the Molecular Deformation Mechanism of Entangled Polymers in Fast Flow by Small Angle Neutron Scattering (with Oak Ridge National Laboratory - 2015-2017)
Project description: In this work, we critically examine the central hypothesis of the tube theory for nonlinear rheology using small angle neutron scattering (SANS).
Responsibilities:
- Evaluate the best processing condition for melt extension by analyzing rheological data for monodispersed deuterated samples;
- Preparing uniform dust-free melt-stretched Neutron Scattering samples by melt-extension followed by liquid nitrogen quenching;