Alice A. K. King

Locking carbon nanotubes in confined lattice geometries--a route to low percolation in conducting composites.

A significant reduction in the electrical percolation threshold is achieved by locking carbon nanotubes (CNTs) in a predominantly hexagonally close-packed (HCP) colloidal crystal lattice of partially plasticized latex particles. Contrary to other widely used latex processing where CNTs are randomly distributed within the latex matrix, for the first time, we show that excluding CNTs from occupying the interior volume of the latex particles promotes the formation of a nonrandom segregated network. The electrical percolation threshold is four times lower in an ordered segregated network made with colloidal particles near their glass transition temperature (T(g)) in comparison to in a random network made with particles at a temperature well above the T(g). This method allows for a highly reproducible way to fabricate robust, stretchable, and electrically conducting thin films with significantly improved transparency and lattice percolation at a very low CNT inclusion which may find applications in flexible and stretchable electronics as well as other stretchable technologies. For instance, our technology is particularly apt for touch screen applications, where one needs homogeneous distribution of the conductive filler throughout the matrix.

A New Raman Metric for the Characterisation of Graphene oxide and its Derivatives.

Raman spectroscopy is among the primary techniques for the characterisation of graphene materials, as it provides insights into the quality of measured graphenes including their structure and conductivity as well as the presence of dopants. However, our ability to draw conclusions based on such spectra is limited by a lack of understanding regarding the origins of the peaks. Consequently, traditional characterisation techniques, which estimate the quality of the graphene material using the intensity ratio between the D and the G peaks, are unreliable for both GO and rGO. Herein we reanalyse the Raman spectra of graphenes and show that traditional methods rely upon an apparent G peak which is in fact a superposition of the G and D’ peaks. We use this understanding to develop a new Raman characterisation method for graphenes that considers the D’ peak by using its overtone the 2D’. We demonstrate the superiority and consistency of this method for calculating the oxygen content of graphenes, and use the relationship between the D’ peak and graphene quality to define three regimes. This has important implications for purification techniques because, once GO is reduced beyond a critical threshold, further reduction offers limited gain in conductivity.

Colloid-Assisted Self-Assembly of Robust, Three-Dimensional Networks of Carbon Nanotubes over Large Areas

Natural materials, such as bone and spider silk, possess remarkable properties as a result of sophisticated nanoscale structuring. They have inspired the design of synthetic materials whose structure at the nanoscale is carefully engineered or where nanoparticles, such as rods or wires, are self-assembled. Although much work has been done in recent years to create ordered structures using diblock copolymers and template-assisted assembly, no reports describe highly ordered, three-dimensional nanotube arrays within a polymeric material. There are only reports of two-dimensional network structures and structures on micrometer-size scales. Here, we describe an approach that uses plasticized colloidal particles as a template for the self-assembly of carbon nanotubes (CNTs) into ordered, three-dimensional networks. The nanocomposites can be strained by over 200% and still retain high conductivity when relaxed. The method is potentially general and so may find applications in areas such as sensing, photonics, and functional composites.

Hypothesis: Bones Toughness Arises from the Suppression of Elastic Waves

Bone and other natural material exhibit a combination of strength and toughness that far exceeds that of synthetic structural materials. Bones toughness is a result of numerous extrinsic and intrinsic toughening mechanisms that operate synergistically at multiple length scales to produce a tough material. At the system level however no theory or organizational principle exists to explain how so many individual toughening mechanisms can work together. In this paper, we utilize the concept of phonon localization to explain, at the system level, the role of hierarchy, material heterogeneity, and the nanoscale dimensions of biological materials in producing tough composites. We show that phonon localization and attenuation, using a simple energy balance, dynamically arrests crack growth, prevents the cooperative growth of cracks, and allows for multiple toughening mechanisms to work simultaneously in heterogeneous materials. In turn, the heterogeneous, hierarchal, and multiscale structure of bone (which is generic to biological materials such as bone and nacre) can be rationalized because of the unique ability of such a structure to localize phonons of all wavelengths.

Predicting the optoelectronic properties of nanowire films based on control of length polydispersity

We demonstrate that the optoelectronic properties of percolating thin films of silver nanowires (AgNWs) are predominantly dependent upon the length distribution of the constituent AgNWs. A generalized expression is derived to describe the dependence of both sheet resistance and optical transmission on this distribution. We experimentally validate the relationship using ultrasonication to controllably vary the length distribution. These results have major implications where nanowire-based films are a desirable material for transparent conductor applications; in particular when application-specific performance criteria must be met. It is of particular interest to have a simple method to generalize the properties of bulk films from an understanding of the base material, as this will speed up the optimisation process. It is anticipated that these results may aid in the adoption of nanowire films in industry, for applications such as touch sensors or photovoltaic electrode structures.

Porous and strong three-dimensional carbon nanotube coated ceramic scaffolds for tissue engineering

Biomaterials research is investigating increasingly complex materials capable of mirroring the highly organized biochemical and architectural environments of the body. Accordingly, tissue scaffolds with nanoscale properties that mirror the fibrous proteins present in tissue are being developed. Such materials can benefit from the inherent dimensional similarities and nanocomposite nature of the cellular environment, altering nanoscale dimensional and biochemical properties to mimic the regulatory characteristics of natural cellular environments. One nanomaterial which demonstrates potential across a diverse range of biomaterial applications is carbon nanotubes (CNTs). Building on previous reports, a method to coat CNTs throughout 3D porous structures is developed. Through modifications to typical chemical vapour deposition (CVD), a high-quality uniform coating of carbon nanotubes (CNTs) is demonstrated over β-tricalcium phosphate/hydroxyapatite (or TCP/HA), which is in clinical use; and the high-mechanical-strength multicomponent ceramic Ca2ZnSi2O7-ZnAl2O4, (or Sr-HT-Gah). The resulting materials address deficiencies of previously reported CNT biomaterials by simultaneously presenting properties of high porosity, biocompatibility and a mechanical stability. Together, this unique combination of properties makes these scaffolds versatile materials for tissue engineering in load bearing applications.

Enhanced Thermal Actuation in Thin Polymer Films Through Particle Nano‐Squeezing by Carbon Nanotube Belts

The continuous development of nanoscale electronic, sensing, and actuating devices requires researchers and manufactures to devise new methods to design materials with nanoscale features and ultimately with projected improvement in performance. The extraordinary mechanical and electronic properties of carbon nanotubes (CNTs) have attracted widespread interest for a range of applications. CNTs exhibit a very low linear expansion coeffi cient, α , (on the order of the α of diamond, ca. 1.1 × 10 − 6 K − 1 ) and a uniquely high thermal conductivity along their longitudinal axis. [ 1 , 2 ] In contrast to CNTs, polymers generally have a higher α , which is dependent on temperature. In amorphous polymers, there are two distinct regions of expansivity with different values of thermal expansion: the glassy (lower α ) and rubbery (higher α ) regions, separated by a phase transition at the glass transition temperature ( T g ). [ 3 ] Furthermore, the α of polymers can be drastically varied by reinforcement with microfi bers, CNTs, and, more recently, graphene oxide sheets. [ 4–6 ]

Considerations for spectroscopy of liquid-exfoliated 2D materials: emerging photoluminescence of N -methyl-2-pyrrolidone

N-methyl-2-pyrrolidone (NMP) has been shown to be the most effective solvent for liquid phase exfoliation and dispersion of a range of 2D materials including graphene, molybdenum disulphide (MoS2) and black phosphorus. However, NMP is also known to be susceptible to sonochemical degradation during exfoliation. We report that this degradation gives rise to strong visible photoluminescence of NMP. Sonochemical modification is shown to influence exfoliation of layered materials in NMP and the optical absorbance of the solvent in the dispersion. The emerging optical properties of the degraded solvent present challenges for spectroscopy of nanomaterial dispersions; most notably the possibility of observing solvent photoluminescence in the spectra of 2D materials such as MoS2, highlighting the need for stable solvents and exfoliation processes to minimise the influence of solvent degradation on the properties of liquid-exfoliated 2D materials.

Selective mechanical transfer deposition of Langmuir graphene films for high-performance silver nanowire hybrid electrodes

In this work, we present silver nanowire hybrid electrodes prepared through the addition of small quantities of pristine graphene by mechanical transfer deposition from surface-assembled Langmuir films. This technique is a fast, efficient, and facile method for modifying the optoelectronic performance of AgNW films. We demonstrate that it is possible to use this technique to perform two-step device production by selective patterning of the stamp used, leading to controlled variation in the local sheet resistance across a device. This is particularly attractive for producing extremely low cost sensors on arbitrarily large scales. Our aim is to address some of the concerns surrounding the use of AgNW films as replacements for indium tin oxide (ITO), namely, the use of scarce materials and poor stability of AgNWs against flexural and environmental degradation.

Biophysical interactions between pancreatic cancer cells and pristine carbon nanotube substrates: Potential application for pancreatic cancer tissue engineering

Novel synthetic biomaterials able to support direct tissue growth and retain cellular phenotypical properties are promising building blocks for the development of tissue engineering platforms for accurate and fast therapy screening for cancer. The aim of this study is to validate an aligned, pristine multi-walled carbon nanotube (CNT) platform for in vitro studies of pancreatic cancer as a systematic understanding of interactions between cells and these CNT substrates is lacking. Our results demonstrate that our CNT scaffolds-which are easily tuneable to form sheets/fibers-support growth, proliferation, and spatial organization of pancreatic cancer cells, indicating their great potential in cancer tissue engineering.