Novel materials based on polymer-grafted nanoparticles (NP) are the focus of this proposal. Since inorganic NPs and organic polymers typically "dislike" each other, these "hairy" particles behave like block-copolymers or amphiphiles. They can, therefore, self-assemble into a range of superstructures when placed in an organic matrix. Understanding the factors controlling NP assembly, and how this assembly state affects the properties of the resulting material are the central issues of interest. As part of this global effort, four questions will be addressed in this proposal, two of which relate to the fundamentals of the assembly process, while the last two refer to the relationship between the NP assembly state and resulting properties: (i) Can the materials science that governs block-copolymer-inspired "hairy" NP assembly be critically delineated ? (ii) Can NP assembly be directed using external fields, e.g., shear, with the ultimate goal of designing membranes with directional transport properties? (iii) Can grafted NPs be assembled at interfaces with the aim of compatibilizing immiscible polymer blends? Note that this proposal will only address experimental aspects here, but shall leverage two parallel theoretical efforts in the PIs group. Thus, a combined theory and experiment based approach will be used to understand the fundamental underpinnings of the applications of this novel class of materials.
NON-TECHNICAL SUMMARY: The main assertion of this proposal is that the control over the spatial distribution of nanoparticles is central to creating new polymeric materials with tunable properties. Thus, it is expected that the proposed work will critically impact a range of novel applications, e.g., self-healing materials, organic photovoltaics, batteries, water purification membranes, drug delivery, and advanced lithography. These transformative research activities are coupled to extensive education and outreach activities. Motivated by recent successes in recruiting high school and undergraduate students for summer research, the PI will recruit (and retain) underrepresented students, both women and minorities, into the Chemical Engineering department at Columbia. The PI is also working with the Chemical Engineering department at the City College of New York and the New York Academy of Sciences to bring together academics in the Greater New York area (faculty and students), local industry and national laboratories in an annual chemical engineering symposium. The goal is, not only to place students into local industry, but also to attract industrial participants into higher degree and/or refresher programs at Columbia.
The chief findings of this work are in the field of nanoparticles chemically grafted with polymeric chains. We showed that the spatial dispersion of hydrophilic, spherical nanoparticles (NPs) in a hydrophobic polymer matrix can be controlled by isotropically grafting the NPs with the polymer chains. These particles behave analogously to amphiphiles (or block copolymers) and assemble into a range of superstructures, when they are placed in a matrix with the same chemical structure as the brush. We also delineated the connection between NP dispersion state and the macroscale properties of the resulting nanocomposite. The results of this work have been published in a variety of journals including Nature Materials (cover graphic ; article cited nearly 250 times to date per Google Docs), three in Nanoletters, one in ACS Macro. Lett. and seven in Macromolecules. It has been the focus of four review articles – Adv. in Chem. & Bio. Eng., a perspective article in Macromolecules, a review in Polymer and an invited review in Adv. Poly. Sci. (in preparation). One patent has already been approved and another is pending. These transformative research activities have been coupled to extensive education and outreach activities. We have had considerable recent success in recruiting high school and undergraduate students for summer research. In fact a recent paper, published in ACS Macro. Lett., represents the work of three such undergraduate students (Stacy Ramcharan, Kendra Windsor, Claire Kearney) pointing to the central role played by these junior researchers in our efforts. Another paper authored by Danmi Lee with preliminary results on the adsorbed block copolymers, a visiting undergraduate student from Imperial College, London just appeared in Advanced Materials. We are also working with the Chemical Engineering department at the City College of New York and the New York Academy of Sciences to bring together academics in the Greater New York area (faculty and students), local industry and national laboratories in an annual chemical engineering symposium. The goal is, not only to place our students into local industry, but also to attract industrial participants into higher degree and/or refresher programs at Columbia.