Multi-Scale Self-Assembly of Nanotube Structures

Carbon nanomaterials such as carbon nanotubes (CNTs), and graphene are entering a fascinating era where their physical properties and synthesis methods are understood well enough to attract industry's interest. The latter is best quantified by the production capacity of CNTs, which is increasing exponentially, and has now reached several thousand tons per year. The success of these materials is fueled by applications including CNT-reinforced composites, and battery electrodes. While impressive, these products typically comprise random mixtures of CNTs whose overall properties are limited compared to what is observed in the constituent individual nanotubes. In part, this is because today's CNT products are processed with traditional manufacturing capabilities, such as injection molding and spray coating. Unfortunately these processes do not enable any structural control over the nanoparticle arrangement, resulting in limited material properties. Future commercial success of new nanocarbon applications will largely depend on our ability to engineer the organization of nanoparticle assemblies.

In this EPSRC first grant, we hypothesize that understanding of physical and chemical interactions between CNTs underlies the self-assembly of new material architectures with properties superior to random mixtures. More precisely, we aim at developing a methodical hierarchical manufacturing approach where nanoparticle organization is systematically optimized at nanoscale, microscale and macroscale dimensions. For this process to be successful we will first seek understanding of the physics and chemistry of inter-particle forces between CNTs. A self-assembly process will then be optimized which uses these inter-particle interactions as a driving force. More precisely, this project builds on a top-down lithographic process previously developed by the PI, and complements this with a new bottom-up self-assembly approach enabling well-defined nanoparticle organization over large substrates.

We envision that the materials developed in this project will be particularly interesting for a variety of diffusion limited processes. These are applications such as battery electrodes, water filters, and catalysis, where the performance of the device is limited by the ability of certain components to diffuse rapidely through the developed material. This can for instance be Li ions in the case of batteries, or water in the case of filters. Unique to the process developed in this project is that it allows for large scale fabrication of CNT assemblies with exceptional control of nanoscale morphology, and micorscale porosity, which is key to engineer the diffusion path. While in depth investigation of for instance battery applications is outside the scope of this project, we will perform preliminary experiments to assess the performance of the developed materials.

1. Academic impact: Aspects of this research project are of interest to various fields of engineering. A first contribution of this project is determining the relative importance and magnitude of different inter-particle forces acting on CNTs. These are fundamental insights that are currently poorly understood, but which may guide the understanding and design of new nanoparticle assembly methods. This includes the formation of high quality CNT coatings as well as complex structured CNT films. We believe this is an enabling technology that may impact CNT applications such as batteries, supercapacitors, biofouling films, transparent conductors, nano-electronics, anisotropic dry adhesives, and catalysis, all topics that are being studied throughout the UK. A second, potentially even more impactful academic outcome will be the way we think about assembling nanomaterials into superstructures. One specific hierarchical CNT self-assembly process will be demonstrated in this project; however, we hope that towards the future this project may inspire other researchers to develop similar types of innovative hierarchical nanoparticle assemblies. Conferences, summer schools, open lab days, e-forums, and other academic outreach venues will be used to to spread the insights gained from this project. Finally, the research associate hired on this project will be trained in a wide variety of processing and characterization techniques at the Cambridge nanocentre. As such, we believe that this project will help him or her to develope a strong track record to either pursue an academic or industrial carreer.

2. Industrial impact: Industrial interest in CNTs has increased substantially over the past years. Due to increased production volumes, and cost reduction, these materials are no longer prohibitive for many applications. However, the industrial development of high-end CNT products requires improved nanotube assembly and processing techniques. This is the field of research this project seeks to impact. It is important to note that Europe, and in particular the UK are playing a leading role in the production of carbon nanomaterials. For instance, Thomas Swan (UK) is the world leader in the fabrication of single wall CNTs, and tools to synthesize carbon nanotubes and graphene, are manufactured in the UK by companies such as Oxford Instruments Plasma Tools, and Surrey Nanosytems. The University of Cambridge also has a strong track record in carbon nanotech spin off companies, such as Q-Flo, CamIn, and Nanoinstruments Ltd. (now Aixtron). UK Start-ups in the field of graphene include Durham Graphene and CrayoNano. Further, multinationals such as Nokia, have research centers located in Cambridge, which are active in the domain of carbon nanomaterials. Through this project, the applicant will actively seek interaction with this industry.

3. Societal impact: Carbon nanomaterials will impact society, both through high-tech applications such as flexible electronics and ultra-lightweight composite materials, as well as by contributing to societal challenges such as water filtration and energy storage. While recent advances in these fields are impressive, we believe that the hierarchical CNT organization pursued in this project will foster further improvements of these applications. Societal importance of this project is also reflected in the fact that this projects fits in many of EPSRC's portfolio activities such as "materials for energy applications", "water engineering", "Graphene and carbon nanotechnology", and "synthetic supramolecular chemistry". Finally, this project seeks to engage with the general public using science as art competitions, e-forums, popular magazines, as well as science fairs. These are activities the applicant has successfully pursued in the past, and which are described in more details in the full project description.