Polymer nanocomposites, mixtures of flexible long-chain molecules (polymers) and hard functional particles, are found in everyday applications from automobile tires to paints and adhesives. To promote the progress of science, the focus of this project is to study polymer nanocomposite coatings that have the potential to improve the ability of solar cell devices to utilize a broader section of the solar spectrum allowing for more efficient energy production. The fundamental issue that the project seeks to address is how to combine dissimilar materials in such a way that the properties can be varied by controlling how well the particles are distributed In addition to experiments, computer simulations will be used to guide the selection of polymer and particles and to help interpret experimental results. Block copolymers, which are two different polymer molecules tied to each other, will be manipulated to create horizontal and vertical alternating domains (like a stack of cards) that contain nanoparticles of complementary functionality. To determine the location of particles and size of aggregates, state-of-the-art characterization tools will be used. This research will produce phase diagrams that allow for the determination of environmental conditions that promote good mixing between the polymer and particles. Besides producing a well-educated, scientifically skilled workforce, the integration of research and education benefits society at several levels. For example, graduate and undergraduate students will participate in annual public events including Nanotechnology Day at Penn, Philly Materials Day, and the Philadelphia Science Festival. An additional exciting outreach program is Girls in Engineering Mathematics and Science Camp (GEMS), a weeklong day-camp that introduces middle-school girls from the Delaware Valley to Science, Technology, Engineering, and Math.

Technical Abstract

The goal of this project is to understand the fundamental principles that control the spatial distribution and assembly of nanoparticles (NPs) in block copolymers (BCPs) and to understand the thermodynamics and phase separation pathways of polymer nanocomposites (PNCs). The overarching goal is to perform systematic studies that build on expertise in polymer and NP diffusion as well as NP assembly in PNCs. (1) The first aim is to tune the nanoscale separation between plasmonic NPs and upconverting nanoplates/nanospheres in horizontally and vertically aligned lamellar BCPs. By functionalizing the NP with polymer brushes, the two NP species will be located in alternating BCP domains. The effect of domain spacing and particle loading will be investigated. PNC field-theoretic simulations (PNC-FT) will be used to determine the free energies of these PNCs and predict the cylinder-to-lamellar phase transition. (2) The second aim is to study the thermodynamic behavior of binary (A/NP) and ternary (A/B/NP) PNCs. The phase diagrams will be mapped out using transmission electron microscopy (TEM) on isothermal samples as well as the new in situ X-ray scattering capabilities. As in the first aim, PNC-FT will provide guidance for selecting materials parameters and help interpret results. (3) The third aim is to investigate phase separation dynamics of binary (A/NP) PNCs to elucidate the fundamental parameters that determine aggregate size and percolating morphologies in kinetically trapped systems. PNC-FT modified to include dynamics will guide experiments and provide insight into the balance between thermodynamics and dynamics that dictate the final morphology. Particle diffusion will be measured using Rutherford backscattering spectrometry. Polymer brush relaxation and ion diffusion through percolated morphologies will also be measured. In summary, although fundamental in nature, the proposed work has the potential to create PNCs with enhanced upconversion luminescence and fast ion mobility, which is of importance for solar energy and energy storage devices, respectively. .

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.

National Science Foundation (NSF)
Division of Materials Research (DMR)
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Andrew Lovinger
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University of Pennsylvania
United States
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