Research Presentation for Prospective Graduate Students [Download]
(1) Micro-dynamics and macroscopic flow of soft solids
Glassy materials form a broad class of amorphous systems which include colloidal and metallic glasses, particulate gels, emulsions and foams, slurries and pastes, and soft particle glasses (SPGs). Despite the large diversity of their composition, they have in common many important features. At rest, they behave like amorphous solids that respond elastically to small perturbations. However, they can deform irreversibly and flow when they experience large enough stresses. This transition from solid to liquid with increasing stress is called yielding. Understanding and controlling how glassy materials yield and flow offer profound insights into the macroscopic rheology and microscopic dynamics of amorphous materials. Furthermore, the question has essential applications in material science and engineering, such as in drilling muds, high-performance coatings, food products, and ceramic pastes. In this project, we use discrete particle simulations and experiments to study shear-induced phase behavior and rheology of a new class of yield stress fluids known as associative SPGs.
Funding source: NSF
(2) Advances in material science using machine learning
Machine learning and artificial intelligence harbor the advent of a new era in material science and its development. This project undertakes the task of discovering new materials with the help of these tools. Some of the notable fields of research undertaken will be in additive manufacturing of polymeric composites, batteries and solid-state polyelectrolytes and sustainable, recyclable polymers.
Funding source: NSF
(3) Modeling and simulations of vitrimer nanocomposites
Vitrimers are polymerics with dynamic covalent crosslinking bonds which allow for rapid rearrangement of the topology at elevated temperatures. This fascinating property of vitrimers can be exercised for easy reprocessing of thermosets. One major drawback of vitrimers from practical applications is that they exhibit significant creep under conditions where thermosets show little to no creep. The primary objective of this research is to use molecular simulations to study the influence of these nanofillers on the kinetics of bond exchange, rheological properties, and creep compliance of the vitrimer matrix. The presence of nanofillers can accelerate the process of bond exchange by either participating in them or providing enhanced surface area for bond exchange reactions to take place. Another aspect of this project is to study the self-assembly of these Polymer Grafted Nanoparticles in the vitrimer matrix. There is exciting research in the field of Polymer Grafted Nanoparticles dispersed in polymer matrices using molecular simulation which has tremendously advanced our understanding of the driving force behind the self-assembly of these nanofillers. The change in the matrix from simple polymeric chains to vitrimers brings into play many variables which could potentially alter our understanding of these systems.
(4) Engineering the interface of incompatible polymer blends
Another research initiative in our group is to use high-performance computing (HPC) and applied mathematics and physics to identify critical factors in enhancing the efficacy of reusing polyethylene (PE) and polypropylene (PP) products, which account for about 60% of the annual global polymer production and are mixed in the plastic waste stream. This project, which is part of the SPSPE sustainable group’s endeavor in providing practical routes for recycling of the waste stream, involves compatibilization of the interface between the PE-PP. Our role here is to understand the migration and bulk-interface partition of compatibilizers. Computational studies on the migration of the compatibilizer molecules and their partitioning will be carried out to compare with the experimental results. Simulations will relate the nanostructure of the interface to the macroscopic mechanics of the system. This project is part of the Reducing Embodied-Energy And Decreasing Emissions (REMADE) Institute’s newly funded research initiatives.
Funding source: REMADE Institute and DOE
(5) Thermodynamics and rheology of shape-memory ionomers
Ionomers are polymers in which ionized groups create ionic crosslinks in the intermolecular structure. They are composed of both neutral and ionized repeat units covalently bonded to the polymer backbone as pendant group moieties. They have long attracted attention due to the physical properties associated with the ions (e.g., conductivity, glass transition, and dynamic bonding) and their interactions with other chemical species (i.e., solvent, salts, and non-ionic repeat units). The primary effects of ionic functionalization of a polymer are to increase the glass transition temperature, melt viscosity, and characteristic relaxation times. Polymer microstructure is also affected, and it is generally agreed that in most ionomers, microphase-separated, ion-rich aggregates form as a result of strong ion–dipole attractions. The major effect of the ionic aggregate was to increase the relaxation processes. This in turn increases the melt viscosity and is responsible for the network-like behavior of ionomers above the glass transition temperature. Coarse-grained MD simulations are used in this project to connect their molecular structure to their macroscopic rheology. In this work, we create ionomer structures with different architectures and study the network formation at different degrees of electrostatic interactions.