Rheology of Polymer Melts with Designed Hairy Nanoparticles

Many essential products, e.g., glass, paper, plastics, and rubbers, are made of polymers. Polymers are highly attractive due to their versatility, low-cost and processability, but their functionality is limited. To enhance the functionality and strength of polymers, it is proposed to incorporate nanoparticles. However, most nanoparticles are often incompatible with polymer matrices, resulting in agglomeration and deterioration in mechanical properties. To control the dispersion of nanoparticles in polymer matrices, chemically grafted polymers on the surface of nanoparticles, known as hairy nanoparticles, is proposed. This award seeks to understand how hairy nanoparticles affect the functionality and properties of the polymers. By controlling the grafted polymer chain length, density, and chemical nature on well-dispersed nanoparticles of different shapes, the research can impact how polymers are manufactured, processed, and utilized for many engineering applications. The proposed research is accompanied by a series of educational and outreach efforts such as involving undergraduate researchers, educational programs for teachers, and releasing open-source codes, to broaden its impact. The rheology of polymer matrices containing hairy nanoparticles cannot be explained by known theories, e.g., Einstein’s or Bachelor’s, which underestimates the relative viscosity by over 10 million folds. The objective of this award, therefore, is to (1) experimentally investigate the rheology of nanocomposites with different shapes of hairy nanoparticles; (2) develop and validate computational tools to simulate such suspensions; and (3) investigate the main reasons for their deviation from the theory, thereby pave the way to improve theoretical/simplified models for advanced manufacturing needs. The proposed study intends to prepare designed 0D,1D, and 2D nanoparticles grafted by poly(methylmethacrylate) or other miscible molecules with different chain lengths and graft densities for dispersion in poly(methylmethacrylate) matrix. Particle-resolved simulations will be performed by handling the moving particles using a sharp-interface immersed boundary method, capable of simulating arbitrary-shaped particles interacting with the fluid. The hairy grafts on the particles will be modeled as a porous medium over the interaction zone derived from experiments. The simulations and experiments will provide sufficient correlation to test several hypotheses on the effect of geometric parameters on rheology, thereby enabling the development of empirical formulas based on these parameters. 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.