A. Amini, N. Hameed, J. S. Church, C. Cheng, A. Asgari, F. Will

Graphene layers (graphite) were deposited on the surface of a NiTi shape memory alloy to enhance the deformation and nanoscale phase transition volume. One highly polished NiTi and one with the graphite deposit were examined. The graphite-coated NiTi showed deeper nanoindentation depths during the solid-state phase transition, especially in rate-dependent zones. Larger superelastic deformation confirmed that nanoscale latent heat transfer through the deposited graphite allowed a larger phase transformed volume in the bulk and, therefore, greater stress relaxation and a greater indentation depth.

A. Amini, C. Cheng, M. Naebe, J. S. Church, N. Hameed, A. Asgari, F. Will

The detection and control of the temperature variation at the nano-scale level of thermo-mechanical materials during a compression process have been challenging issues. In this paper, an empirical method is proposed to predict the temperature at the nano-scale level during the solid-state phase transition phenomenon in NiTi shape memory alloys. Isothermal data was used as a reference to determine the temperature change at different loading rates. The temperature of the phase transformed zone underneath the tip increased by ~3 to 40 °C as the loading rate increased. The temperature approached a constant with further increase in indentation depth. A few layers of graphene were used to enhance the cooling process at different loading rates. Due to the presence of graphene layers the temperature beneath the tip decreased by a further ~3 to 10 °C depending on the loading rate. Compared with highly polished NiTi, deeper indentation depths were also observed during the solidstate phase transition, especially at the rate dependent zones. Larger superelastic deformations confirmed that the latent heat transfer through the deposited graphene layers allowed a larger phase transition volume and, therefore, more stress relaxation and penetration depth.

A. A. Walker, S. Weisman, J. S. Church, D. J. Merritt, S. T. Mudie, T. D. Sutherland

Raspy crickets (Orthoptera: Gryllacrididae) are unique among the orthopterans in producing silk, which is used to build shelters. This work studied the material composition and the fabrication of cricket silk for the first time. We examined silkwebs produced in captivity, which comprised cylindrical fibers and flat films. Spectra obtained from micro-Raman experiments indicated that the silk is composed of protein, primarily in a beta-sheet conformation, and that fibers and films are almost identical in terms of amino acid composition and secondary structure. The primary sequences of four silk proteins were identified through a mass spectrometry/cDNA library approach. The most abundant silk protein was large in size (300 and 220 kDa variants), rich in alanine, glycine and serine, and contained repetitive sequence motifs; these are features which are shared with several known beta-sheet forming silk proteins. Convergent evolution at the molecular level contrasts with development by crickets of a novel mechanism for silk fabrication. After secretion of cricket silk proteins by the labial glands they are fabricated into mature silk by the labium-hypopharynx, which is modified to allow the controlled formation of either fibers or films. Protein folding into beta-sheet structure during silk fabrication is not driven by shear forces, as is reported for other silks.

Y-S. Li, J. S. Church, A. L. Woodhead

Iron oxide magnetic nano-particles (MNPs) have been prepared in aqueous solution by a modified coprecipitation method. Surface modifications have been carried out using tetraethoxysilane (TEOS),triethoxysilane (TES) and 3-aminopropyltrimethoxysilane (APTMS). The uncoated and coated particle products have been characterized with transmission electron microscope (TEM), energy dispersive X-ray (EDX) spectroscopy, infrared (IR) and Raman spectroscopy, and thermal gravimetric analysis (TGA). The particle sizes were determined from TEM images and found to have mean diameters of 13, 16 and 14 nm for Fe₃O₄, TES/Fe₃O₄ and APTMS/Fe₃O₄, respectively. IR and Raman spectroscopy has been applied to study the effect of thermal annealing on the uncoated and coated particles. The results have shown that magnetite nano-particles are converted to maghemite at 109 °C and then to hematite by 500 °C. In contrast, the study of the effect of thermal annealing of micro-crystalline magnetite by IR spectroscopy revealed that the conversion to hematite began by 300 °C and that no maghemite could be identified as an intermediate phase. IR spectra and TGA measurements revealed that the Si–H and 3-aminopropyl functional groups in TES and APTMS coated magnetite nano-particles decomposed below 500 °C while the silica layer around the iron oxide core remained unchanged. The molecular ratio of APTMS coating to iron oxide core was determined to be 1:7 from the TGA data. Raman scattering signals have indicated that MNPs could be converted to maghemite and then to hematite using increasing power of laser irradiation in a manner similar to that observed for thermal annealing.

M. G. Huson, J. S. Church, J. M. Poole, S. Weisman, A. Sriskantha, A. C. Warden, P. M. Campbell, J. A. M. Ramshaw, T. D. Sutherland

Honeybee larvae produce silken cocoons that provide mechanical stability to the hive. The silk proteins are small and nonrepetitive and therefore can be produced at large scale by fermentation in E. coli. The recombinant proteins can be fabricated into a range of forms; however the resultant material is soluble in water and requires a post production stabilizing treatment. In this study, we describe the structural and mechanical properties of sponges fabricated from artificial honeybee silk proteins that have been stabilized in aqueous methanol baths or by dry heating. Aqueous methanol treatment induces formation of ß-sheets, with the amount of ß-sheet dictated by methanol concentration. Formation of ß-sheets renders sponges insoluble in water and generates a reversibly compressible material. Dry heat treatments at 190 °C produce a water insoluble material, that is stiffer than the methanol treated equivalent but without significant secondary structural changes. Honeybee silk proteins are particularly high in Lys, Ser, Thr, Glu and Asp. The Properties of the heat treated material are attributed to generation of lysinoalanine, amide (isopeptide) and/or ester covalent cross-links. The unique ability to stabilize material by controlling secondary structure rearrangement and covalent cross-linking allows us to design recombinant silk materials with a wide range of Properties.

J. Y. Cai, J. Min, J. McDonnell, J. S. Church, C. D. Easton, B. Humphries, S. Lucas, A. Woodhead

We report a method for modifying carbon nanotube (CNT) spun yarns with aryldiazonium salts that involves the pH controlled application of the diazonium salts to CNTs both during and after the yarn formation process. This largely facilitates the chemical accessibility to CNTs within the yarn, potentially enabling a more extensive and uniform modification. The modified CNT yarns were characterised by X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electron microscopy, and also examined for their mechanical properties. The results demonstrated that a CNT spun yarn was effectively modified by this method without impairing the yarn integrity. The formation of oligomerised polyene structures on the CNT surfaces was observed. This modification resulted in an increase in tensile strength and Young’s modulus of the CNT yarn. The functional groups grafted on CNTs also provide opportunities to form crosslinks in the yarn to further improve mechanical properties.

J. A. Schutz, J. S. Church

People who work in hazardous Environments under high physiological stress often have to weigh up the benefits and difficulties of wearing respiratory protection. By developing filter materials that provide comparable smoke particle protection at a significantly lower breathing Resistance, exposure to physiological stress may be reduced without jeopardizing protection. In this paper, we investigate to this end the use of stationary electrostatic surface Charges, which are known to dramatically improve the efficiency of filter media to fine particles at next to no change in breathing resistance. Filtration test results presented show that some high temperature polymer fiber materials commonly used for personal protective equipment can in fact reach best practice filtration performance if combined with a suitable fiber counterpart. Tribo-electric fiber blends made from combinations of polypropylene with poly-imide-amide, poly(m-phenylene benzimidazole), meta-polyaramid or para-polyaramid have been found to generate significant electrostatic enhancements in nonwoven needle felts that are stable over time. Results suggest that polypropylene is an essential component of fiber blends that reach best practice electrostatic performance with the exception of a meta-aramid fiber blended with wool that appears to work as well. As a result, it is possible to manufacture heat resistant garments for respiratory protection against smoke particles, which could be similar to a bandana and provides protection at a reduced breathing resistance.

A. J. Poole, R. E. Lyons, J. S. Church

Feather keratin has been widely studied for use as a bio-based material. In this paper, we dissolve feather keratin using industrial sodium sulfide to investigate the yield, dissolved keratin characteristics, and properties of regenerated products to assess the potential of using sodium sulfide as a means of converting waste feathers into a biopolymer. Optimal conditions appeared to require short incubation times in order to give maximum strength in the regenerated product. This limits the yield to approximately 55%. Air-dried films and acid-precipitated samples are all readily re-crosslinked, suggesting the re-crosslinking process is robust. Minimizing exposure to the highly alkaline conditions appears favorable to final product strength through minimizing alkaline chain damage. The β-sheet structure of the parent keratin is largely maintained. The regenerated keratin was shown to have potentially attractive physical properties for use as a bio-polymer.