NSF Award
2400474
Non-Technical Abstract: Research Initiation Awards provide support for junior and mid-career faculty at Historically Black Colleges and Universities who are building new research programs or redirecting and rebuilding existing research programs. It is expected that this award helps to further the faculty member’s research capability and effectiveness, improves the breadth and depth of research and teaching at the home institution, trains graduate students in previously unexplored areas, and involves undergraduate students in research experiences. This interdisciplinary project at Tennessee State University seeks to discover the underlying mechanism behind the premature cracking or distortion of polymers in contact with specific fluids including solvents, oils, release agents, detergents, and lubricants. The research results are expected to aid in synthesis of new materials resistant to such failure, thus cutting down losses in time and money, and alleviating safety concerns associated with the use of commercial plastics in major engineering applications including medical devices, biomedical adhesives, packaging, wire jacketing, and automobile interiors. This research trains graduate and undergraduate students in the areas of polymer mechanics and material characterization, opens new career pathways, and contributes to the initiation of a materials science program at the home institution.<br/><br/>Technical Abstract: This project unifies mechano-sorptive creep and environmental stress cracking, currently studied as independent phenomena. The research team aims to develop a constitutive material model which can capture non-equilibrium chemo-mechanical behavior under the combined action of mechanical loading and solvent influx as a function of polymer meso-structure, polymer-solvent interaction, temperature, and stress. The material model incorporates the following key features: (a) relaxation of volume conservation under fluid sorption by the polymer to account for unsaturated or partially saturated conditions, (b) transition across glassy, viscoelastic and rubbery regimes under fluid sorption or temperature change, (c) two-way coupling between stress and chemical potential via a proposed free energy in the framework of poroviscoelasticity. The model parameters are calibrated using a combination of molecular dynamics simulation, multi-modal experimentation combining time-based Fourier Transform Infrared microscopy with micro-tensile testing, and sorption experiments. Both the simulation and experiment are expected to reveal and validate the critical underlying mechanism of chemical potential-stress coupling. Furthermore, the model parameters are functions of the material composition and chemistry, thus providing valuable input to the synthesis of materials resistant to mechano-sorptive creep and environmental stress cracking. By demonstrating these behaviors to be two extremes of the same phenomena, this project will facilitate a rich exchange of information and ideas between two currently separated streams of research. Furthermore, the constitutive law is expected to bridge between multi-temperature thermomechanical poroviscoelastic models and phenomenological models developed for cellulose-based materials that predict mechano-sorptive creep. The work is also expected to quantify the contributions of “molecular Velcro” and macroscopic stress gradients to the overall mechano-sorptive behavior of polymeric materials.<br/><br/>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.
