Adam J. Clancy

Optimised exfoliation conditions enhance isolation and solubility of grafted graphenes from graphite intercalation compounds

In bulk applications, it is essential that graphene sheets disperse individually in solvents or matrices, and therefore, suitable functionalisation regimes are crucially important. Here, isolated, highly soluble, alkyl-grafted graphenes were synthesised by reacting exfoliated Na-reduced graphite intercalation compounds (GIC) with alkyl halides. In this reaction, efficient exfoliation of the Na-reduced GICs into individually-dispersed negatively-charged graphenes provides accessible surface area for grafting. Increasing the alkyl chain length leads to large decrease of the grafting ratio (GR), demonstrating that steric factors also play an important role. However, optimising the Na concentration (C/Na ratio) in the reaction was very effective for improved exfoliation and increased GR. The X-ray diffraction measurements suggest that particular C/Na ratios (C/Na = ∼12) led to full exfoliation, by balancing total charge and charge condensation effects and that the GR can be significantly increased even in the case of long alkyl chains (eicosyl chains), corresponding to a high solubility of 37 μg ml−1 and high yield in o-dichlorobenzene. Moreover, the absolute Na concentration is the critical parameter, with the same optimum (∼0.01 M) for exfoliation and grafting of GIC at all graphite concentrations; it was possible to graft even at high graphite concentration (0.3 M (3.6 mg ml−1)) successfully.

Applying a potential difference to minimise damage to carbon fibres during carbon nanotube grafting by chemical vapour deposition

The application of an in situ potential difference between carbon fibres and a graphite foil counter electrode (300 V, generating an electric field ca 0.3-0.7 V μm-1), during the chemical vapour deposition synthesis of carbon nanotube (CNT) grafted carbon fibres, significantly improves the uniformity of growth without reducing the tensile properties of the underlying carbon fibres. Grafted CNTs with diameters 55 nm ± 36 nm and lengths around 10 μm were well attached to the carbon fibre surface, and were grown without the requirement for protective barrier coatings. The grafted CNTs increased the surface area to 185 m2 g-1 compared to the as-received sized carbon fibre 0.24 m2 g-1. The approach is not restricted to batch systems and has the potential to improve CNT grafted carbon fibre production for continuous processing.

Fast Exfoliation and Functionalisation of Two-Dimensional Crystalline Carbon Nitride by Framework Charging

2D layered graphitic carbon nitride nanosheets offer tunable electronic and chemical properties. However, exfoliation and functionalisation of gCN for specific applications remains challenging. We report a scalable one-pot reductive method to produce solutions of single and few layer 2D gCN nanosheets with excellent stability in a high mass yield (35%) from polytriazine imide. High resolution imaging confirms the intact crystalline structure and identifies an AB stacking. The first successful deliberate organic functionalisation of dissolved gCN is illustrated, providing a general route to adjust their properties.

Increasing carbon fiber composite strength with a nanostructured “brick-and-mortar” interphase

Conventional fiber-reinforced composites suffer from the formation of critical clusters of correlated fiber breaks, leading to sudden composite failure under tension. To mitigate this problem, an optimized “brick-and-mortar” nanostructured interphase was developed, in order to absorb energy at fiber breaks and alleviate local stress concentrations whilst maintaining effective load transfer. The coating was designed to exploit crack bifurcation and platelet interlocking mechanisms known in natural nacre. However, the architecture was scaled down by an order of magnitude to allow a highly ordered conformal coating to be deposited around conventional structural carbon fibers, whilst retaining the characteristic phase proportions and aspect ratios of the natural system. Drawing on this bioinspiration, a Layer-by-Layer assembly method was used to coat multiple fibers simultaneously, providing an efficient and potentially scalable route for production. Single fiber pull-out and fragmentation tests showed improved interfacial characteristics for energy absorption and plasticity. Impregnated fiber tow model composites demonstrated increases in absolute tensile strength (+15%) and strain-to-failure (+30%), as compared to composites containing conventionally sized fibers.