Luke C. Henderson

Structure inducing ionic liquids-enhancement of alpha helicity in the Abeta(1-40) peptide from Alzheimer's disease

We have studied the impact of ionic liquid solvents on the structure of the Abeta(1-40) peptide from Alzheimers disease and found that ionic liquid solvents were able to induce a conformational change in the structure of the Abeta(1-40) peptide. This conformational change impacts the self-assembly of the peptide into amyloid fibrils.

Domino Heck-Aza-Michael Reactions: Efficient Access to 1-Substituted Tetrahydro-β-carbolines

A simple and efficient palladium-catalyzed domino reaction for the synthesis of a series of C1-substituted tetrahydro-beta-carbolines is described. This domino process involves a Heck reaction at the indole 2-position of a halogenated tryptamine precursor, followed by intramolecular aza-Michael addition.

Rapid and efficient protic ionic liquid-mediated pinacol rearrangements under microwave irradiation

Several protic ionic liquids were tested as potential mediators for pinacol rearrangements employing microwave irradiation. Using hydrobenzoin as a model substrate, the optimal conditions were found to be heating at 80 °C for 5 min using H2SO4:triethylamine as the ionic liquid. A key feature of this reaction was to keep the microwave power low (20 W) to avoid ionic liquid degradation. Application of these conditions to triphenylethylene glycol gave rearrangement products in high yield and purity, while phenylethylene glycol and styrene oxide gave pinacol products that underwent a cascade aldol condensation. These conditions represent an efficient means by which pinacol rearrangements can be carried out while avoiding the use of strong Bronsted acids, high temperatures and extended reaction times.

Design Rules for Enhanced Interfacial Shear Response in Functionalized Carbon Fiber Epoxy Composites

Carbon-fiber reinforced composites are ideal light-weighting candidates to replace traditional engineering materials. The mechanical performance of these composites results from a complex interplay of influences operating over several length and time scales. The mechanical performance may therefore be limited by many factors, one of which being the modest interfacial adhesion between the carbon fiber and the polymer. Chemical modification of the fiber, via surface grafting of molecules, is one possible strategy to enhance interactions across the fiber-polymer interface. To achieve systematic improvements in these modified materials, the ability to manipulate and monitor the molecular structure of the polymer interphase and the surface grafted molecules in the composite is essential, but challenging to accomplish from a purely experimental perspective. Alternatively, molecular simulations can bridge this knowledge gap by providing molecular-scale insights into the optimal design of these surface-grafted molecules to deliver superior mechanical properties. Here we use molecular dynamics simulations to predict the interfacial shear response of a typical epoxy/carbon-fiber composite for both pristine fiber and a range of surface graftings. We allow for the dynamic curing of the epoxy in the presence of the functionalized surface, including cross-link formation between the grafted molecules and the polymer matrix. Our predictions agree with recently reported experimental data for these systems and reveal the molecular-scale origins of the enhanced interfacial shear response arising from functionalization. In addition to the presence of interfacial covalent bonds, we find that the interfacial structural complexity, resulting from the presence of the grafted molecules, and a concomitant spatial homogeneity of the interphase polymer density are beneficial factors in conferring high interfacial shear stress. Our approach paves the way for computational screening processes to design, test, and rapidly identify viable surface modifications in silico, which would enable rapid systematic progress in optimizing the match between the carbon fiber treatment and the desired thermoset polymer matrix.

A novel approach to functionalise pristine unsized carbon fibre using in situ generated diazonium species to enhance interfacial shear strength

Complex molecules have been successfully grafted onto the surface of unsized carbon fibre, a heterogeneous material which is a challenge to functionalise. The in situ generation of highly reactive phenyldiazo-species from their corresponding anilines was employed to achieve this task. The success of an initial proof-of-concept study (bearing a nitro moiety) supported by X-ray Photoelectron Spectroscopy (XPS) and physical characterisation, led to the design and synthesis of a more complex compound possessing a pendant amine moiety which could theoretically react with an epoxide based resin. After attachment to unsized oxidised fibres, analysis by XPS of the resulting fibres (fluorine used as an XPS tag) indicated a marked difference in functionalisation success which was attributed to steric factors, shown to be critical in influencing the attachment of the phenyldiazo-intermediate to the carbon fibre surface. Analysis of key fibre performance parameters of these fibres showed no change in elastic modulus, strength, surface topography or microscopic roughness when compared to the control unsized oxidised fibres. The functionalised fibres did however show a large increase in coefficient of friction. Single fibre fragmentation tests indicated a marked increase in interfacial shear strength, which was attributed to the pendent amine functionalities interacting with the epoxy resin.

Rhodium(II) Azavinyl Carbenes and their Recent Application to Organic Synthesis

This highlight solely focusses on the synthetic applications of azavinyl rhodium(II) carbenes derived from N-sulfonyl triazoles. An overview of their use in intermolecular reactions to form a variety of heterocycles is examined, in addition to intramolecular annulations and rearrangements.

Tailoring the fibre-to-matrix interface using click chemistry on carbon fibre surfaces

A convenient and effective strategy to control the surface chemistry of carbon fibres is presented, comprising electro-chemical reduction of aryl diazonium salts onto the surface, followed by ‘click chemistry’ to tether the desired surface characteristic of choice. The power of this approach was demonstrated by engineering a small-molecule interface between carbon fibre and an epoxy matrix improving interfacial shear strength by up to 220%, relative to unmodified control fibres. The techniques used in this work do not impede the fibre performance in tensile strength or Youngs modulus. This work provides a platform upon which any carbon fibre-to-resin interface can be easily and rapidly designed and implemented.

Rapid surface functionalization of carbon fibres using microwave irradiation in an ionic liquid

The modification of carbon fibre surfaces has been achieved using a novel combination of low power microwave irradiation (20 W) in both an ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) and an organic solvent (1,2-dichlorobenzene). The use of the ionic liquid was superior to the organic solvent in this application, resulting in a higher density of surface grafted material. As a consequence, carbon fibres treated in the ionic liquid displayed improved interfacial adhesion in the composite material (+28% relative to untreated fibres) compared to those treated in organic solvent (+18%). The methodology presented herein can be easily scaled up to industrially relevant quantities and represent a drastic reduction in both reaction time (30 min from 24 h) and energy consumption, compared to previously reported procedures. This work opens the door to potential energy and time saving strategies which can be applied to carbon fibre manufacture for high performance carbon fibre reinforced composites.

Determination of Kamlet–Taft parameters for selected solvate ionic liquids

The normalised polarity E and Kamlet-Taft parameters of recently described solvate ionic liquids, composed of lithium bis(trifluoromethyl)sulfonimide (LiTFSI) in tri- () or tetraglyme () have been determined and compared to the parent glyme ( and ). We show that these solvate ionic liquids have a high polarity (, (E) = 1.03; , (E) = 1.03) and display very high electron pair accepting characteristics (, α = 1.32; , α = 1.35). Molecular dynamics simulations suggest that the chelated lithium cation is responsible for this observation. The relatively small hydrogen bond acceptor (β) values for these systems (, β = 0.41; , β = 0.37) are thought to be due primarily to the TFSI anion, which is supplemented slightly by the glyme oxygen atom. In addition, these solvate ionic liquids are found to have a high polarisability (, π* = 0.94; , π* = 0.90).

A Novel Approach to the Functionalisation of Pristine Carbon Fibre Using Azomethine 1,3-Dipolar Cycloaddition

We demonstrate the utilisation of an azomethine 1,3-dipolar cycloaddition reaction with carbon fibre to graft complex molecules onto the fibre surface. In an effort to enhance the interfacial interaction of the fibre to the matrix, the functionalised fibres possessed a pendant amine that is able to interact with epoxy resins. Functionalisation was supported by X-ray photoelectron spectroscopy and the grafting process had no detrimental effects on tensile strength compared with the control (untreated) fibres. Also, microscopic roughness (as determined by atomic force microscopy) and fibre topography were unchanged after the described treatment process. This methodology complements existing methodology aimed at enhancing the surface of carbon fibres for advanced material applications while not compromising the desirable strength profile. Single-fibre fragmentation tests show a statistically significant decrease in fragment length compared with the control fibres in addition to transverse cracking within the curing resin, both of which indicate an enhanced interaction between fibre and resin.