Collaborative Research: Directed Assembly of Nanoparticles and Polymers via Co-Crystallization

Drexel University, Philadelphia PA

Investigators

Abstract

Nanoparticles ranging from one to a hundred nanometers are one of the most important building blocks for advanced functional materials and have demonstrated intriguing optical, electronic, and mechanical properties. This project aims to fabricate ordered nanoparticle-polymer superstructures by co-crystallizing linear crystalline polymers and inorganic nanoparticles. Polymers are soft and flexible, while inorganic nanoparticles are stiff and rigid. They are unlikely to co-exist in a regular crystalline structure. However, recent work shows that they co-crystallize into unusual structures, such as hollow spheres, by controlling the chemistry and crystallization conditions. This project will systematically investigate how to fabricate and control these novel co-assembled structures. It is anticipated that a library of unprecedented nanoparticle-polymer superstructures will be formed, and these structures could find applications in bioimaging and drug delivery. The educational component of the proposal includes (1) mentoring graduate and undergraduate students, exposing them to polymer/nanoparticle synthesis, crystallization, and advanced characterization; (2) developing modules on nanoparticle assembly for graduate courses; (3) involving high school students and teachers, particularly under-represented populations, in the proposed research activities. Crystalline polymers and nanoparticles are dissimilar motifs that can co-assemble to form superstructures. Nanoparticles have slower relaxation, more sluggish diffusion, and stronger interparticle interactions than polymers. Because of the contrasting symmetry demands for dense packing and the distinct structure formation kinetics, the co-crystallization of these dissimilar motifs can produce unconventional hybrid structures, such as hollow spherical crystals with a bilayer shell composed of nanoparticles and crystalline polymer, denoted as nanoparticle crystalsomes. This project aims to investigate the co-crystallization of tailor-designed nanoparticles and polymers, focusing on novel structures arising from the incommensurability of the two structural motifs. Accordingly, the specific aims of the projects are: (1) understanding the co-crystallization process of polymer and nanoparticles; (2) controlling the nanoparticle crystalsome structure via co-crystallization; (3) tuning nanoparticle crystalsomes by varying the shape and dynamics of the constituent motifs. Significant intellectual merits include: (1) A novel scientific approach for co-crystallizing dynamically and topologically asymmetric motifs will be established. (2) The kinetics aspect of the approach will elucidate the complex interplay between the ligand exchange and polymer crystallization kinetics in the nanoparticle crystalsome formation process. 3) The structural aspect of the approach will be established based on a packing mismatch theory. 4) A library of unprecedented nanoparticle-polymer superstructures will be formed. These structures will have controlled characteristics such as size, opening, and curvature, which would otherwise be unattainable. 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.