Mark Hughes

Charge transfer in carbon nanotube actuators investigated using in situ Raman spectroscopy

Charge transfer dynamics on the surface of single-wall carbon nanotube sheets is investigated using in situ Raman spectroscopy in order to understand the actuation mechanism of an electrochemical actuator and to determine associated parameters. We built an actuator from single-wall carbon nanotube mat and studied its actuation in several alkali metal (Li, Na, and K) and alkaline earth (Ca) halide and sulfate solutions in order to clarify the role of counterion as mobile ions in the film. The variation of bonding with applied potential was monitored using in situ Raman spectroscopy. This is because Raman can detect changes in C–C bond length: the radial breathing mode at ∼190 cm−1 varies inversely with the nanotube diameter, and the G band at ∼1590 cm−1 varies with the axial bond length. In addition, the intensities of both the modes vary with the emptying/depleting or filling of the bonding and antibonding states due to electrochemical charge injection. We discussed the variation of peak height and wave n...

A retrospective study of viral and Toxoplasma gondii infections in 54 liver transplant recipients in Cambridge

Abstract Viral and Toxoplasma gondii infections are known to be a major cause of morbidity and mortality in renal and cardiac transplant recipients, but few detailed studies have been performed on liver transplant patients. We have therefore made a retrospective serological analysis of these infections in 54 liver transplant recipients in the Cambridge/Kings College Hospital series. Twenty-seven (50%) patients experienced active cytomegalovirus (CMV) infection, some acquiring the infection from the donated organ. Ten (18·5%) were found to have had herpes simplex virus (HSV) infections. Fewer patients suffered varicellazoster virus (VZV), Epstein-Barr virus (EBV), adenovirus and T. gondii infections. One patient succumbed to primary donor-acquired T. gondii infection.

Doping and Electrochemical Capacitance of Carbon Nanotube-Polypyrrole Composite Films

Abstract : Composite films were electrochemically synthesised via the simultaneous deposition of multiwalled nanotubes and polypyrrole, a conducting polymer. Negatively charged functional groups attached to the surface of the acid treated nanotubes enables the tubes to act as a dopant for the PPy in these films. Scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy revealed that the nano-porous three-dimensional arrangement of PPy coated MWNTs in these films produced specific capacitances per mass and geometric area as high as 192 F/g and 1.0 F/sq cm. respectively. This value of specific capacitance per geometric area exceeds that of both component materials and other carbon nanotube-conducting polymer composites. The composite films described in this report were also able to charge and discharge more than an order of magnitude faster than similarly prepared pure PPy films. The nano-porosity and small diffusion distances within the composite films, crucial to achieving the superior capacitive performance, were found to be dependent on the concentration of nanotubes and additional dopant anions in the polymerisation electrolyte, offering possibilities for tailoring of the composite structure.

Electrochemical Tuning of Single-Wall Carbon Nanotube Mat and Investigations on Actuator Mechanism

Electrochemical tuning of single-wall carbon nanotubes has been investigated using in situ Raman spectroscopy. We built a linear actuator from single-wall carbon nanotube mat and studied in several alkali metal (Li, Na, and K) and alkaline earth (Ca) halide solutions. The variation of bonding with electrochemical biasing was monitored using in situ Raman. This is since Raman can detect changes in C-C bond length: the radial breathing mode (RBM) at ∼190 cm −1 varies inversely with the nanotube diameter and the G band at ∼1590 cm −1 varies with the axial bond length. In addition, the intensities of both the modes vary significantly in a nonmonotonic manner pointing at the emptying/depleting or filling of the bonding and anti-bonding states - electrochemical charge injection. We discuss the variation of spectroscopic observables (intensity/frequency) of these modes providing valuable information on the charge transfer dynamics on the single-wall carbon nanotubes mat surface. We found the in-plane compressive strain (∼ -0.25%) and the charge transfer per carbon atom (f c ∼ -0.005) as an upper bound for the electrolytes used i.e. CaCl 2 . These results can be quantitatively understood in terms of the changes in the energy gaps between the one-dimensional van Hove singularities in the electron density of states arising possibly due to the alterations in the overlap integral of π bonds between the p orbitals of the adjacent carbon atoms. Moreover, the extent of variation of the absolute potential of the Fermi level or alternatively modification of band gap is estimated from modeling Raman intensity to be around 0.1 eV as an upper bound for CaCl 2 .