Chemical Engineering Seminar

In this talk, I will present two examples of designing and engineering macromolecules for energy and environmental sciences. First, I will describe the synthesis of a new type of porous carbon fibers from block copolymers. Carbon fibers possess high surface areas and rich functionalities for interacting with ions, molecules, and particles. However, the control over their porosity has remained challenging. Conventional syntheses rely on blending polyacrylonitrile with sacrificial additives, which macrophase-separate and result in poorly-controlled pores. Here we use the microphase-separation of block copolymers to synthesize porous carbon fibers with well-controlled mesopores and micropores. Without infiltrating any precursors or dopants, block copolymers are directly converted to nitrogen and oxygen dual-doped porous carbon fibers. Owing to the optimized bimodal pores and interconnected porous network, the block copolymer-based porous carbon fibers exhibit outstanding ion transport properties and ultrahigh capacitances in supercapacitors. The use of block copolymer precursors revolutionizes the synthesis of carbon fibers. The advanced electrochemical properties signify that porous carbon fibers represent a new platform material for electrochemical catalysis, energy storage and conversion.

Second, I will present the design of a new polymer nanocomposite membrane for highly energy-efficient speakers. Membranes are ubiquitous in natural and man-made systems including ears and drums. Emerging technologies demand for membranes that are ultrathin but over an ultra-large area. Additionally, the membranes must be flexible, lightweight, transparent, conductive, tensioned, and free-standing. The construction and actuation of these membranes, however, has been challenging. Here we show a bilayer membrane of polymer and single layer graphene that is free-standing, highly tensioned, flexible, lightweight, transparent, and conductive and has an unprecedentedly high aspect-ratio of 105. Separately, neither the single-atom-thick graphene nor the polymer layer survives suspension over inch scale, let alone repeated mechanical deformation. After integration, the two components mutually reinforce each other and support 30,000 times their own weight. Upon electromechanical actuation, the membrane pushes a massive amount of air and generates high-quality acoustic sound, and it is 100 times more energy efficient than state-of-the-art electrodynamic speakers. The new bilayer polymer composite will impact a plethora of fields and enable next-generation technologies in acoustics, electronics, mechanics, optics, and chemistry.