Studying Carbon Nanotubes on the Mesoscale: Physical Properties and Emergent Phenomena

自从1991年Iijima首次对碳纳米管进行表征以来，人们对其物理性质和应用进行了大量的研究。虽然碳纳米管作为一种材料显示出了希望，但无法生产出工业规模的产品限制了它们的实际应用。在解决这一问题的各种工艺中，浮动催化剂化学气相沉积(FCCVD)工艺在块状碳纳米管材料的生产中具有相当大的学术和工业意义。这一过程产生了稀薄的碳纳米管网络材料，称为气凝胶，然后可以加工成连续的碳纳米管纤维和复合材料。了解气凝胶和其他碳纳米管结构在FCCVD和任何后续工艺中是如何形成的，对于优化制造工艺和根据特定应用定制材料性能至关重要。PHD的目的是使用计算方法研究碳纳米管结构的形成和物理性质。为了获得合适的计算时间，采用了自适应中尺度方法，使含有数亿个碳原子的系统能够进行模拟。这些模拟还可以用来测量所得材料的有效物理属性，例如对负载的机械阻力或电导和热导。特别令人感兴趣的是由于不同的微结构而不是单个碳纳米管的性质而出现的现象。例如，从隔离到导电行为的转变称为电渗流，以及从单个碳纳米管到碳纳米管纤维或块状材料的导电性的缩放。

Since the first characterisation of carbon nanotubes (CNTs) by Iijima in 1991, a considerable amount of research has been conducted on their physical properties and applications. While CNTs as a material have shown promise, an inability to generate industrial quantities has limited their practical application. Among a variety of processes proposed to address this problem, the Floating Catalyst Chemical Vapour Deposition (FCCVD) process is of considerable academic and industrial interest for bulk CNT material production. The process produces dilute CNT network materials referred to as aerogels which can then be processed into continuous CNT fibres and composite materials. Developing an understanding of how aerogels and other CNT structure form during FCCVD and any subsequent process is critical in optimising the manufacturing process and tailoring material properties to specific applications.The aim of the PhD is to study the formation and physical properties of CNT structures using computational methods. In order to achieve suitable computation times, adaptive mesoscale methods are used which enable simulations of systems containing hundreds of millions of carbon atoms. These simulations can also be used to measure effective physical properties of the resulting material, such as mechanical resistance to load or electrical and thermal conductivities. Of particular interest are phenomena that emerge due to different microstructures rather than the properties of the individual CNTs. Examples are the transition from isolating to electrically conductive behaviour called electrical percolation as well as scaling of the electrical conductivity from individual CNTs to CNT fibres or bulk materials.