Collaborative Research: Mechanics of End-Linked Polymer Networks with Strain-Induced Crystallization Regulated by Topological Defects

About This Grant

End-linked polymer networks are macromolecules that can be highly stretchable, tough, yet involving low accumulated damage over cyclic loads, making them promising next-generation load-bearing soft materials. Their excellent mechanical properties rely on the potential giant and reversible strain-induced crystallization, which is regulated by defects in the material and with temperature. However, the coupling between strain-induced crystallization, topological defects, temperature, and the corresponding mechanical properties of end-linked polymer networks remains poorly understood. This award will support fundamental research to combine experimental and modeling approaches in understanding mechanisms and developing new end-linked polymer networks with desired mechanical properties. The fundamental understanding developed from this project will benefit the society by enabling novel strong and tough soft materials that can maintain their excellent properties over cyclic loads, hence facilitating emerging applications such as soft robotics, medical devices, and wearable electronics. In addition, the project will bring broader impacts in the education and training of graduate and undergraduate students by introducing students to emerging industrial needs through a new university-industry workshop. The outcomes of the research will be integrated into core undergraduate courses and multiple well-organized outreach activities such as the high school Building Bridges program and the Research Experiences for Teachers Summer Institute, with an expectation to engage a diverse group of students. The objective of this research is to investigate the fundamental role of topological defects in regulating the strain-induced crystallization in end-linked polymer networks at the microscale, as well as their stress-strain behaviors, fracture, and fatigue properties at the macroscale. To achieve this goal, the project will study a model material system and focus on topological defects of dangling chains and cyclic loops with quantitative tunability. The research will combine experiment and modeling at two length scales, including mechanical characterization at the macroscale and in-situ X-ray scattering characterization at the microscale. The two length scales will be linked by a continuum thermodynamic model, a microscopic polymer fracture model, and a numerical finite element model. The collaborative research will investigate stress-strain responses across a wide range of temperatures, as well as fracture and fatigue behaviors of the model end-linked polymer network. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.