(6bp) Polymer/Nanomaterial Structural Control Using Flow and Confinement: Modeling, Experiment, and Applications

With the rise of innovative nanoscale material science over the past decade, efforts to combine the versatility of polymer with novel functionalities of nanofillers have substantially increased. Recent studies have found that a strategic structural placement of these materials within a polymer can dictate the composite material properties, whether it is electrical, mechanical, or thermal. Gaining control over such structures is crucial in enhancing material properties significantly to tailor to wide variety of modern applications such as battery, sensory, and protective gear. Evidently, the nanoscale structure of these nanocomposites can greatly influence their macroscopic properties. The challenge lies in controlling the structure of the so-called nanocomposite material to tailor to the application of one's choice at will. 

To this end, I have sought answers to the following questions: i) how does the polymer/nanofiller composite structure change under various processing conditions? And ii) how does its functionality change with the corresponding structure and subsequently used as in a real-life application? To effectively answer these questions, I have done a comprehensive study of modeling, experiment, and application on polymer/nanofiller composite structure under various processing conditions.

Using coarse-grained molecular dynamics, multiple combinations of polymer(homopolymer or block copolymers) and nanofillers(nanoparticles, nanorods, and nanotubes) composite structures under A) shear and extensional flow^[2,5] and B) cylindrical nanoscale confinement^[1,3,4] were investigated. Our study reveals that depending on the control variables of the aforementioned dynamics, we can induce novel functional structures such as highly oriented polymer and nanomaterials, evenly placed nanomaterials within polymer matrix, and interconnected nanorods. 

As a comparative experiment, electrospinning was used to fabricate polymer/nanofiller nanofibers which undergoes both extensional deformation and nanoscale cylindrical confinement^[1,3,5]. The structural agreement between the simulation and the experiment result confirms the validity of the model. As such, some of the novel structures observed in simulation were also observed in experiment, such as well-dispersed and well-aligned nanorods within the nano-scale polymer fibers. The novel functional properties that arise from nanostructures of electrospun nanofiber are then readily utilized in various applications such as molecular sensors^[5] and battery electrodes^[6].

Lastly, preliminary work has been done to significantly increase the mechanical strength of electrospun polymeric fibers by improving the molecular orientation and degree of crystallinity from gel-electrospinning ultra high molecular weight polyethylene. By defining a fundamental connection between the predicted nanostructure and its functionality, we can expand much further on the capabilities of electrospun nanofibers to significantly impact the polymer processing and its application as a whole.

Selected Publications

[1]      J. H. Park, V. Kalra, and Y. L. Joo, “Cylindrically Confined Assembly of Asymmetrical Block Copolymers with and without Nanoparticles: Simulation and Experiment”, Soft Matter, 2012, 8, 1845.

[2]      J. H. Park, V. Kalra, and Y. L. Joo, “Controlling the Dispersion and Orientation of Nanorods in Polymer Melt under Shear: Coarse-Grained Molecular Dynamics Simulation Study”, Journal of Chemical Physics, 2014, 140, 124903.

[3]      J. H. Park, J. Yin, V. Kalra, and Y. L. Joo, “Role of Nanoparticle Selectivity in the Symmetry Breaking of Cylindrically Confined Block Copolymers”, Journal of Physical Chemistry C, 2014, 118, 7653–7668.

[4]      J. H. Park and Y. L. Joo, “Formation of Interconnected Morpholgies via Nanorod Inclusion in Confined Assembly of Symmetric Block Copolymers”, Physical Chemistry Chemical Physics, 2014, 16, 8865 - 8871.

[5]      J. H. Park and Y. L. Joo, “Tailoring Nanorod Alignment in a Polymer Matrix by Elongational Flow under Confinement: Simulation, Experiments, and Surface Enhanced Raman Scattering Application”, Soft Matter, 2014, 10, 3494-3505.

[6]      J. Yin, J. Carlin, J. J. Kim, Z. Li, J. H. Park, B. Patel, S. Chakrapani, S. H. Lee, and Y. L. Joo, “Synergy between Metal Oxide Nanofibers and Carbon Substrates for Rechargeable Lithium-Oxygen Batteries”, Advanced Energy Materials 2015, 5, 1401412