This research aims to probe how molecular design of chain architecture can be employed to affect nonlinear dynamics of entangled polymers. The proposed research will attempt to control the structure of long-chain branching (LCB) in various polyisoprene and polybutadiene-based melts, and determine the differences between melts with LCB and corresponding linear melts under different conditions of large deformation. The specific objectives of the proposed work are as follows: 1) Determine interfacial yielding characteristics of the various LCB polymers to contrast with corresponding linear counterparts; 2) Explore how melt strength depends on the specific chain architecture, e.g., the number of branching points per chain; 3) Examine whether the entanglement network with LCB may suffer strain localization upon large deformation; 4) Identify key molecular structural parameters that define/determine the cohesion and dictates nonlinear responses to large deformations; 5) Study the effect of mixing different components of LCBs or LCB and linear chains on the nonlinear dynamics. To achieve these goals, both simple and uniaxial extension will be carried out involving either startup or step strain. In all cases, effective particle-tracking velocimetric (PTV) observations will be indispensable and systematically carried out. In the case of shear, a circular Couette shear cell will be employed with PTV capability. Uniaxial extension will be realized either with the counter-rotating double-cylinder device or Instron where in situ PTV measurements will also be performed.
This research aims to explore and identify guiding fundamental principles that may find application in more efficient and energy-saving manufacturing of polymeric materials. These principles will ultimately emerge from the present proposed work, aimed to determine how different molecular designs of polymeric materials would affect the processing ability of plastics and rubbers. The outcome of the proposed work should lead to explicit information valuable to the plastic and rubber industries. At the same time, the experimental activities are expected to stimulate theoretical development in the field of polymer physics. More broadly, the PI plans to consolidate the findings from this research into a textbook, which would include all the key results emerging from his contributions to this field. Since the nature of the proposed research is visualization-intensive, complex physical phenomena can receive intuitive interpretations, thus providing attractive educational materials for students in middle and high schools to perceive how science is done. As part of the research activities, an international collaboration has also been initiated with the Changchun Institute of Applied Chemistry of the Chinese Academy of Sciences, aiming to carry out computer simulations complementary to the various proposed experiments.