(6gp) Understanding and Controlling the Mechanical Properties of Polymeric Networks

The mechanical properties of polymer networks are vitally important to the performance of materials, their dynamic response under force activation and their longtime stability.  Emerging applications of polymeric networks in energy, biomedical engineering, and defense technologies demand further advancement in understanding the structure-mechanics relationship, as well as development of methods that allow predicative control over mechanical properties of materials.

In this poster, I will present my graduate research on understanding and controlling the mechanical properties of model associating polymeric networks.  First, I investigate the network relaxation hierarchy over a large window of length scales and time scales.  By combining various experimental techniques such as mechanical spectroscopy, forced Rayleigh scattering and nuclear magnetic resonance, I identify two major deviations from the ideal Maxwellian behavior, which originate from the presence of dynamic inhomogeneity and the difference between the Rouse time of network strands and the junction dissociation time.  Next, I demonstrate a new approach to control the mechanics of associating networks by manipulating the molecular architecture of network constituents.  Specifically, topological entanglement is engineered into the network to drastically slow down the relaxation of polymer chains at long times.  This strategy effectively improves the materials’ toughness, extensibility, creep resistance and stability in solutions.  The entanglement effect and mechanical properties are further controlled by introducing short grafts or branches on the polymer architecture.  Experiment results show qualitative agreement with predictions from sticky Rouse and sticky reptation theories.  Finally, I will discuss new synthetic approaches to prepare hybrid macromolecules mimicking the biological functions and mechanical properties of natural mucins and proteoglycans.  

In the future, I would like to carry research towards (1) unraveling the complex structure-property relationship in complex natural biomaterials, and (2) developing new platform technologies to prepare multifunctional materials interfacing with living matters.