CAREER: Overcoming Heterogeneity: Ultra-monodisperse Semiconducting Carbon with Parts per Million and Billion Polydispersity

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

TECHNICAL SUMMARY: The overarching objective of this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, is to uncover and develop fundamentally new ways for realizing ultra-monodisperse semiconducting single-walled carbon nanotubes. This work will explore novel strategies in the post-synthetic separation and sorting of nanotubes using nanotube-differentiating conjugated polymers, while at the same time implement metrologies for quantifying monodispersity that are needed to advance the differentiation and sorting. Certain classes of conjugated polymers such as polyfluorenes are unusually effective semiconducting nanotube-discriminating agents, for example discerning by electronic-type so powerfully that under the proper conditions the conjugated polymers will not measurably disperse nanotubes that are metallic. Currently, very little is known about these polymers and how they interact with nanotubes. However, with a better understanding of the materials chemistry of nanotube-polymer interactions, it should become possible to realize nanotubes that that are so monodisperse that their bandgap polydispersity can be counted in only parts per million and their electronic-type polydispersity in parts per billion (whereas current nanotube monodispersity is typically measured in parts per hundred). Focused research will be pursued in 4 areas: (1) Exploration and implementation of metrology that can quantify "impurity" nanotubes at vanishing concentrations; (2) Fundamental experimentation designed to understand the materials chemistry and thermodynamics of nanotube / differentiating polymer binding; (3) Investigation of the role of defects on polymer-nanotube binding; and (4) Implementation of single- and multi-step dispersion and post-dispersion differentiation. NON-TECHNICAL SUMMARY: Since their discovery in 1991, carbon nanotubes have tantalized scientists and the general public, as well, due to their unique structure and exceptional properties. These materials promise to help overcome many of society's grand challenges in electronics, energy, and medicine. However, this promise has not yet been realized because of nanotubes' heterogeneity, which is both physical and electronic. Recently, a promising class of polymers has been discovered that can be used to select for specific types of carbon nanotubes and thereby dramatically reduce their heterogeneity. This project will uncover fundamental details regarding the materials chemistry of the interactions between nanotubes and the polymers. The understanding that is gained will then be used to create carbon nanotubes that are sufficiently ultra-monodisperse to enable applications that have long been hyped but inhibited by heterogeneity. In conjunction with the technical project, outreach will be conducted to inspire youth to enter science, technology, engineering, and mathematics (STEM) fields and increase educational opportunities for under-represented groups. For example, a hands-on STEM-based workshop for middle school students entitled "E3-Engineering, Energy, and the Environment" will be created and implemented. The workshop will engage students in materials science topics with an energy and environmental hook (such as energy efficient or energy harvesting materials), teach creative problem-solving, inspire the next-generation of scientists and engineers, and involve undergraduate and graduate students in mentoring and outreach experiences.