Emiliano Bilotti

Fabrication and property prediction of conductive and strain sensing TPU/CNT nanocomposite fibres

In this study, thermoplastic polyurethane (TPU) fibres containing multi-walled carbon nanotubes (MWNTs) and fabricated via an extrusion process were demonstrated to possess a tuneable level of electrical conductivity. A simple approach based on the time–temperature superposition applied to the electrical conductivity of carbon nanotube (CNT) percolating in a thermoplastic polyurethane (TPU) melt was also developed to predict the conductivity of the nanocomposite fibres. The observation of Arrhenius dependence of zero-shear viscosity and the assumption of simple inverse proportionality between the variation of conductivity, due to network formation, and viscosity allow a universal plot of time variation of conductivity to be composed, which is able to predict the conductivity of the extruded fibres. The same TPU/CNT fibres were also demonstrated to possess good strain sensing abilities, which makes them good candidates for applications in smart textiles.

Investigation into the structural, morphological, mechanical and thermal behaviour of bacterial cellulose after a two-step purification process.

Bacterial cellulose (BC) is a natural hydrogel, which is produced by Acetobacter xylinum (recently renamed Gluconacetobacter xylinum) in culture and constitutes of a three-dimensional network of ribbon-shaped bundles of cellulose microfibrils. Here, a two-step purification process is presented that significantly improves the structural, mechanical, thermal and morphological behaviour of BC sheet processed from these hydrogels produced in static culture. Alkalisation of BC using a single-step treatment of 2.5 wt.% NaOH solution produced a twofold increase in Youngs modulus of processed BC sheet over untreated BC sheet. Further enhancements are achieved after a second treatment with 2.5 wt.% NaOCl (bleaching). These treatments were carefully designed in order to prevent any polymorphic crystal transformation from cellulose I to cellulose II, which can be detrimental for the mechanical properties. Scanning electron microscopy and thermogravimetric analysis reveals that with increasing chemical treatment, morphological and thermal stability of the processed films are also improved.

The use of carbon nanotubes for damage sensing and structural health monitoring in laminated composites: a review

Abstract The increasing use of fiber-reinforced plastics (FRPs) in industries such as aerospace, marine, and automotive, has resulted in a necessity to monitor the structural integrity of composite structures and materials. Apart from development of traditional non-destructive testing methods which are performed off-line, there is a growing need to integrate structural health monitoring (SHM) systems within composite structures. An interesting route toward multifunctional composite materials with integrated SHM capabilities is through the introduction of carbon nanotubes (CNTs) in fiber-reinforced composites as this provides not only integrated damage sensing capability, but may, at the same time, also lead to some additional mechanical reinforcement. Since the first use of CNTs for damage sensing in composite laminates, a significant number of studies have dealt with this topic, but a systematic understanding on the use of CNTs in FRPs for SHM is still lacking. Furthermore, a significant gap remains between results obtained in the laboratory and industrial applications. This review reports on the progress of this topic so far. The reviewed work had been categorized from model studies on single fiber composites to laminated composites under different loading conditions, as well as the development of reliable damage-sensing systems which could be transferred to real applications.

Integrated damage sensing in fibre-reinforced composites with extremely low carbon nanotube loadings

A nanoengineered hybrid composite system has been developed, with integrated damage sensing capabilities at extremely low carbon nanotube (CNT) contents. The employed simple spray coating technique offers good spatial control and the possibility of localized CNT deposition, especially near the fibre/matrix interface, solving traditional problems associated with the incorporation of nanofillers in fibre-reinforced composite laminates such as increased resin viscosity and filtering effects. Moreover, the employed spraying technology has good potential for industrial scale-up. In situ damage sensing based on standard composite tests has been demonstrated for the first time on hybrid glass fibre/CNT composites using extremely low CNT loadings (below 0.1 wt.%) and shows great potential for localized structural health monitoring by controlled CNT deposition into damage prone zones.

Dynamic percolation in highly oriented conductive networks formed with different carbon nanofillers

Dynamic percolation in highly oriented conductive networks formed with different carbon nanofillers is investigated during disorientation upon annealing. Conductive networks are constructed by solid-state drawing, subsequent annealing, and using fillers with different dimensions (multiwalled carbon nanotubes (MWCNTs) and carbon black (CB)) in a bicomponent tape. Interestingly, it is observed that a less entangled network work is formed by mixed filler containing CB; consequently, this result in an accelerated dynamic percolation process and reduced activation energy of such process. Three different analytical approaches have been utilized to analyze this interesting behavior. It is concluded that the dynamic percolation process in highly oriented conductive polymer composites filled with MWCNTs can indeed be accelerated by the addition of CB, since less entangled networks are formed in a hybrid filler system compared with MWCNTs alone.

In Situ Exfoliation of Graphene in Epoxy Resins: A Facile Strategy to Efficient and Large Scale Graphene Nanocomposites

Any industrial application aiming at exploiting the exceptional properties of graphene in composites or coatings is currently limited by finding viable production methods for large volumes of good quality and high aspect ratio graphene, few layer graphene (FLG) or graphite nanoplatelets (GNP). Final properties of the resulting composites are inherently related to those of the initial graphitic nanoparticles, which typically depend on time-consuming, resource-demanding and/or low yield liquid exfoliation processes. In addition, efficient dispersion of these nanofillers in polymer matrices, and their interaction, is of paramount importance. Here we show that it is possible to produce graphene/epoxy nanocomposites in situ and with high conversion of graphite to FLG/GNP through the process of three-roll milling (TRM), without the need of any additives, solvents, compatibilisers or chemical treatments. This readily scalable production method allows for more than 5 wt % of natural graphite (NG) to be directly exfoliated into FLG/GNP and dispersed in an epoxy resin. The in situ exfoliated graphitic nanoplatelets, with average aspect ratios of 300-1000 and thicknesses of 5-17 nm, were demonstrated to conferee exceptional enhancements in mechanical and electrical properties to the epoxy resin. The above conclusions are discussed and interpreted in terms of simple analytical models.

Nanoscale interfacial electroactivity in PVDF/PVDF-TrFE blended films with enhanced dielectric and ferroelectric properties

The typical limitations of ferroelectric polymers like poly(vinylidene fluoride) (PVDF) – low crystallinity and indirect ferroelectric β-phase crystallization – and poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) – high materials and processing costs and a low Curie point – are tackled by a simple and industrially viable melt blending approach. Despite the immiscible nature of PVDF and PVDF-TrFE, strong interactions exist between the two polymers, which substantially affect the morphology and texture of the blends as well as their dielectric and ferroelectric properties. Surprisingly, minor amounts of PVDF-TrFE lead to a significant increase in the β-phase content and preferred orientation of PVDF, well beyond the rule-of-mixtures. Moreover, the blends exhibit maximum increases in the dielectric constant of 80% and 30%, respectively, compared with pure PVDF and PVDF-TrFE. The ferroelectric remnant polarization increases from 0.040 to 0.077 C m−2, while the coercive field decreases from 75 to 32 kV mm−1 with increasing PVDF-TrFE content from 0 to 40 wt%. The enhancement of properties is explained by the strong interactions at the interfaces between PVDF and PVDF-TrFE, which also suppress the Curie transition of PVDF-TrFE, providing a potentially increased working temperature range for blended films, which is important in applications like non-volatile energy storage devices, ferroelectric field-effect transistors and touch sensors.

Measured efficiency of a ZnO nanostructured diode piezoelectric energy harvesting device

We used controlled bending of a ZnO/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) diode at known strain rates to measure the mechanical-to-electrical energy conversion efficiency. The mechanical energy input into the nanostructured diode was measured as 330 ± 2 nJ cm−2. The electrical energy output was calculated by integrating the product of the short-circuit current and open-circuit voltage over time. This gives a measured external efficiency of the device at a bending rate of 500 mm/min of 0.0067%. The efficiency increased exponentially with bending rate, though this increase must slow as the mechanical coupling efficiency is approached, which gives a maximum possible efficiency of 23% for ZnO.

Dependence of surface free energy on molecular orientation in polymer films

Surface free energy of mechanically drawn polycarbonate films was determined using contact angle measurements and shown to increase with orientation. The increase in polymer film surface free energy was attributed to increased polymer chain packing during orientation, supported by film density measurements, which provides enhanced intermolecular interactions. Surface free energy can therefore be increased by, or used to predict, polymer orientation.

Enhanced Thermal and Electrical Properties of Polystyrene-Graphene Nanofibers via Electrospinning

Polystyrene- PS- graphene nanoplatelets GNP 0.1, 1, and 10 wt.% nanofibers were successfully produced via electrospining of dimethyformamide- DMF- stabilized GNP and PS solutions. Morphological analysis of the composite nanofibers confirmed uniform fiber formation and good GNP dispersion/distribution within the PS matrix. The good physical properties of GNP produced by liquid exfoliation were transferred to the PS nanofibers. GNP modified PS nanofibers showed a 6-fold increase in the thermal conductivity and an increase of 7-8 orders of magnitude in electrical conductivity of the nanofibers at 10 wt.% GNP loading.