Cristina Vallés

• PhD in Materials Science
• Researcher at The University of Manchester

Due to an increasing demand for more portable and intelligent electronic devices, strong and flexible fibers which are also electrically conductive and thermally stable are currently on demand. Herein, wet-spun nylon/graphene nanoplatelets (GNPs) and nylon/reduced graphene oxide (rGO) nanocomposite fibers were fabricated in a range of filler loadin...

Coal tar pitch (CTP) is a residue formed from the distillation of coal tar and is widely used as a carbonizable and graphitizable binder for many industrial applications. However, CTP is fossil-derived and has recently been classified as a “sunset” status material under REACH due to its toxicity, which makes finding a sustainable alternative vital....

Composite phase change materials (CPCMs), consisting of nanofillers embedded inside conventional PCMs such as salt hydrates or paraffins, are emerging andidates for large-scale latent heat storage systems or electro-chemical applications. High thermal conductivity and thermal diffusivity of CPCMs are crucial prerequisites for practical utilization,...

The potential for the use of copper coatings on steel switching mechanisms is abundant owing to the high conductivities and corrosion resistance that they impart on the engineered assemblies. However, applications of these coatings on such moving parts are limited due to their poor tribological properties; tendencies to generate high friction and s...

Applications of copper coatings on steel switching mechanisms are abundant owing to their high conductivities and corrosion resistance that they impart on the engineered assemblies. However, applications of these coatings on such moving parts are limited due to their poor tribological properties; tendencies to generate high friction and susceptibil...

Applications of copper coatings on metal components are abundant owing to their high conductivities, corrosion resistance and anti-bacterial properties. However, applications of these coatings on moving parts are limited due to their poor tribological properties; tendencies to generate high friction and susceptibility to degradative wear. In this s...

Graphene and its derivatives have shown fascinating potential in biomedical applications. However, the biocompatibility of graphene with vascular smooth muscle cells (VSMCs) and applications to vascular engineering have not been explored extensively. Using a rat aortic smooth muscle cell line, A7r5, as a VSMC model, we have explored the effects of...

Carbon is widely used as the electrode material in supercapacitors but has not reached its maximum performance due to poor optimization of electrode-electrolyte interaction. Taking inspiration from recent advances in “water in salt” electrolytes where the electrochemistry changes significantly due to the scarcity of free water, we propose a new ele...

Graphene oxide (GO) is an attractive alternative to graphene for many applications due to its captivating optical, chemical, and electrical characteristics. In this work, GO powders with a different amount of surface groups were synthesized from graphite via an electrochemical two-stage process. Many synthesis conditions were tried to maximize the...

In order to realise the potential of graphene nanocomposites it is vital to control the degree of dispersion and achieve a strong graphene polymer interface. Herein, we developed a facile grafting to functionalisation approach for graphene nanoplatelets. NH2-terminated graphene nanoplatelets, NH2 GNPs, prepared by a diazonium coupling were used as...

This work investigates the evolution of the tensile and structural properties of fused filament fabrication (FFF), formed polymers under gamma irradiation. Commercial off-the-shelf print filaments of Poly(lactic acid) (PLA), Thermoplastic polyurethane (TPU), Chlorinated polyethylene elastomer (CPE), Nylon, Acrylonitrile butadiene styrene (ABS) and...

In order to realise the potential of graphene nanocomposites it is vital to control the degree of dispersion and achieve a strong graphene/polymer interface. Herein, we developed a facile ‘grafting to’ functionalization approach for graphene nanoplatelets. NH2-terminated graphene nanoplatelets (NH2-GNPs) prepared by diazonium coupling were used as...

Electromagnetic interference (EMI) shielding coating materials with thicknesses in the microscale are required in many sectors, including communications, medical, aerospace and electronics, to isolate the electromagnetic radiation emitted from electronic equipment. We report a spray, layer-by-layer (LbL) coating approach to fabricate micron thick,...

Electromagnetic interference (EMI) shielding coating materials with thicknesses in the microscale are required in many sectors, including communications, medical, aerospace and electronics, to isolate the electromagnetic radiation emitted from electronic equipment. We report a spray, layer-by-layer (LbL) coating approach to fabricate micron thick,...

The development of scalable Out of Autoclave (OoA) in situ thermoset curing methods are required to overcome important drawbacks related to the autoclave based processing methods typically used in industry. The incorporation of graphene, an electrothermal carbon nanomaterial with the ability to transform electric energy into heat through Joule heat...

Poly(ether ether ketone) (PEEK), with its superb mechanical properties, excellent chemical resistance and high thermo-oxidative stability is one of the most important engineering thermoplastics for high-end applications. In this work, we investigate the elastic and viscoelastic properties along with the creep mitigation of two sets of samples: PEEK...

The effects of surfactants of different nature (anionic, cationic and non-ionic) and chain length on the morphology, microstructure, thermal stability and electrical resistivity of liquid exfoliated graphene (G) were investigated. Microscopic (SEM and AFM) observations revealed that the thickness of G in the dispersions depended on the surfactant n...

Electrically conductive composites comprising polymers and graphene are extremely versatile and have a wide range of potential applications. The conductivity of these composites depends on the choice of polymer matrix, the type of graphene filler, the processing methodology, and any post-production treatments. In this review, we discuss the progres...

The development of scalable Out-of-Autoclave (OoA) in-situ thermoset curing methods are required to overcome important drawbacks related to the autoclave-based processing methods typically used in industry. The incorporation of graphene, an electrothermal carbon nanomaterial with the ability to transform electric energy into heat through Joule heat...

This paper investigates the effects of graphene nanoplatelets (GNP) on combustion behaviour of epoxy resin (ER). In particular it presents, for the first time, a numerical modelling methodology that quantifies the effects of GNP in reducing the peak rate of heat release of epoxy resin with different amounts and types of GNP. Five different GNP/ER c...

A detailed study has been undertaken of the mechanisms of stress transfer in polymeric matrices with different values of Young's modulus, Em, reinforced by graphene nanoplatelets (GNPs). For each material, the Young's modulus of the graphene filler, Ef, has been determined using the rule of mixtures and it is found to scale with the value of Em. Ad...

Printed graphene supercapacitors have the potential to empower tomorrow's wearable electronics. We report a solid-state flexible supercapacitor device printed on textiles using graphene oxide ink and a screen-printing technique. After printing, graphene oxide was reduced in situ via a rapid electrochemical method avoiding the use of any reducing re...

The exceptional mechanical properties, high functionality and ultra-high aspect ratio, combined with the capacity to form liquid crystalline (LC) phases at very low concentrations (~0.1 wt.%) in water and organic solvents leading to perfectly aligned structures, makes graphene oxide (GO) a new class of soft material. Graphene mesophases raise parti...

Contradictions in the reported biocompatibility of graphene-related materials have been attributed to differences in their preparation. Herein, we address the conflicting behavior of different pristine graphene dispersions through their careful preparation and characterization in aqueous media. Although exfoliated in different media, all graphene d...

Secondary electron emission is a limiting factor for a performance of many instruments ranging from small gauges and detectors to waveguides and charged particle accelerators. Several methods have been developed to reduce this effect, e.g. use of a coating of a material with low Secondary Electron Yield (SEY). This paper describes the effect of gra...

The spatial orientation of the reinforcing elements in polymer-based composites plays a vital role in controlling mechanical properties but there is no generally-accepted way of quantifying the spatial orientation at the nanoscale of plate-like fillers in nanocomposites. A previous study found that the intensity of scattering of the Raman band is d...

The effect of the C/O ratio of graphene oxide materials on the reinforcement and rheological percolation of epoxy-based nanocomposites has been studied. As-prepared graphene oxide (GO) and thermally-reduced graphene oxide (TRGO) with higher C/O ratios were incorporated into an epoxy resin matrix at loadings from 0.5 to 5 wt %. Tensile testing revea...

The effect of the lateral dimensions of the graphene reinforcement on the physical properties of poly(methyl methacrylate) (PMMA) nanocomposites was studied. Electrochemically-exfoliated few-layer graphene with average diameters of 5 μm (5-FLG) and 20 μm (20-FLG) were incorporated into a PMMA matrix at loadings from 0.5 to 20 wt.% by melt mixing us...

We present an energy efficient, green and facile approach to the successful reduction of graphene oxide (GO) materials using molten halide flux at 400°C. GO materials have been synthesized by a modified Hummers method and subsequently reduced for periods of up to 8 h. Reduced GO (rGO) flakes have been characterized using X-ray-diffraction (XRD), Ra...

The rheological behaviour of concentrated aqueous dispersions of graphene oxide (GO) was studied as a model system and then compared to those of GO in poly(methyl methacrylate) (PMMA). Dynamic and steady shear tests were conducted using a parallel plate rheometer. The aqueous system behaved as a reversibly flocculated dispersion with linear viscoel...

Graphene shows excellent potential as a structural reinforcement in polymer nanocomposites due its exceptional mechanical properties. We have shown previously that graphene composites can be analysed using conventional composite theory with the graphene flakes acting as short fillers which have a critical length of ~3 µm for good reinforcement. Her...

In this communication we present a potentiometric aptasensor based on chemically modified graphene (transducer layer of the aptasensor) and aptamers (sensing layer). Graphene oxide (GO) and reduced graphene oxide (RGO) are the basis for the construction of two versions of the aptasensor for the detection of a challenging living organism such as Sta...

Graphene oxide (GO) prepared using the Hummers’ method is known to be composed of functionalized graphene sheets decorated by strongly-bound oxidative debris that can be removed by a simple base wash. The use of as-made GO and base-washed GO as reinforcing fillers in poly(methyl methacrylate) (PMMA) nanocomposites has been compared through dynamic...

We show that the two-component model of graphene oxide (GO), that is, composed of highly oxidized carbonaceous debris complexed to oxygen functionalized graphene sheets, is a generic feature of the synthesis of GO, independent of oxidant or protocol used. The debris present, roughly one-third by mass, can be removed by a base wash. A number of tech...

Treatment of graphene oxide (GO) with sodium hydroxide separates the material into two components: a colourless, but highly fluorescent, oxidative debris and a darker non-fluorescent material containing the graphene-like sheets. The as-produced GO shows a weak, broad photo-luminescence while the oxidative debris fluoresces more intensely, blue-shif...

The development of ion-selective electrodes (ISEs) using solid-state transducer materials is of great interest for advanced potentiometric detection systems. At present, conducting polymers are the most used solid-state transducing materials. However, their reliability is strongly related to their chemical stability and the formation of internal wa...

Thermodynamics drive the spontaneous dissolution of a graphite intercalation compound (GIC) KC(8) in NMP to form stable solutions. Reduction potential of graphene is measured at +22 mV vs. SCE. Single layer graphene flakes (ca. 1 μm(2)) have been unambiguously identified by electron diffraction.

We report the formation of a solid-state charge-transfer complex upon simultaneous reduction of a graphene oxide–polyaniline (GO-PANI) composite consisting of GO sheets coated by a thin layer of PANI. The reduced R(GO-PANI) material exhibits an unprecedented donor–acceptor interaction at the interface between RGO sheets and the thin PANI layer coat...

In this article we present a general introduction to the field of graphene and in particular of graphene-based composites. The opportunities for achieving novel high performance composite materials with enhanced properties are highlighted and the challenges to be overcome discussed. As the application of graphene as a nanofiller in composite materi...

The coordination of three different ambidentate phosphorus ylides [Ph3P=CHC(O)Me], [Ph3P=CHC(O)OMe] and [Ph3P=CHCN] towards differentpalladium and platinum substrates with one or two vacant coordinative positions has been studied. In all examined cases a complete selectivity on the bonding position and mode has been found, since C-bonded ylides are...

The coordination of three different ambidentate phosphorus ylides [Ph3P=CHC(O)Me], [Ph3P=CHC(O)OMe] and [Ph3P=CHCN] towards different palladium and platinum substrates with one or two vacant coordinative positions has been studied. In all examined cases a complete selectivity on the bonding position and mode has been found, since C-bonded ylides ar...

Industrial, CVD multi-walled carbon nanotubes are shown to form true solutions by reduc-tion with alkali metals and subsequent exposure to polar solvents such as DMSO. Addition of an electrophile such as bromo-decanoic acid allows functionalization of the tubes. The whole process, dissolution and functionalization includes no harsh treatment such a...

Multi-walled carbon nanotubes were highly aggregated into ropes after their synthesis by chemical vapour deposition and, therefore, two different methods for disentangling the bundles of nanotubes were studied. One method compared the use of mild and vigorous mechanical treatments in ethanol and the other one employed dispersants in aqueous media....

Multi-walled carbon nanotubes (MWCNTs) were produced in a chemical vapor deposition (CVD) process employing methane and argon as hydrocarbon and carrier gas over supported sol–gel Co–Mo/MgO catalysts. A detailed study about the influence of the gas flow of both hydrocarbon and carrier gas on carbon yield, morphology, structure and graphitization de...

Negatively charged graphene layers from a graphite intercalation compound spontaneously dissolve in N-methylpyrrolidone, without the need for any sonication, yielding stable, air-sensitive, solutions of laterally extended atom-thick graphene sheets and ribbons with dimensions over tens of micrometers. These can be deposited on a variety of substrat...

Carbon nanotubes with a drastically reduced number of graphitic layers were synthesized in high yield by chemical vapor deposition of methane over a sol–gel Mo–Co catalyst supported on magnesium oxide particles. We show that both the catalyst composition and the methane flow rate strongly influence the porosity of the catalyst support, the catalyst...

The in-situ polymerization of aniline in the presence of multiwalled carbon nanotubes and (S)-(+)-10-camphorsulfonic acid provides a route to optically active composite materials. Their chiroptical properties suggest that polymers and composite materials adopt similar optical properties indicative of “compact coil” in DMSO and “extended coil” in m-...

The mixed ylide−pyridinium salts [Ph3PC(H)C(O)CH2NC5H5]Cl (2a) and [Ph3AsC(H)C(O)CH2NC5H5]Br (15) have been prepared by reaction of the P and As ylides [Ph3PC(H)C(O)CH2Cl] and [Ph3AsC(H)C(O)CH2Br] (14), respectively, with pyridine. These ylides react with Pd(II) salts in the presence of bases, affording the four-membered C,C-chelated complexes cis-...

Sulfur is introduced as an additive in CVD processes for the production of carbon nanotubes over Co–Mo/MgO sol–gel catalysts employing two different approaches: for the first time as sulfonated Co–Mo/MgO sol–gel catalysts and, alternatively, as thiophene vapour during the CVD reaction process. On one hand, the use of sulfur compounds during the sol...

Excess molar enthalpies, densities, speeds of sound, and viscosities at the temperatures (283.15, 298.15, and 313.15) K have been measured for the binary mixture 2-methyltetrahydrofuran + 1-butanol. From the experimental data, excess molar volumes, excess isentropic compressibilities, excess speeds of sound, and viscosity deviations have been calcu...

A novel Ni-Y/Mo catalyst has been prepared for the chemical vapor deposition (CVD) synthesis of carbon nanotubes (CNT) using methane as carbon precursor. It was observed that the carbon deposit generated by the catalyst was formed by filaments gathered together in large bundles or rope-like structures. It was found that Ni-Y/Mo catalyst was adequat...

Large numbers of multi-wall carbon nanotubes have been produced using a Co-Mo sol-gel catalyst with a high Mo/Co ratio. Carbon yields up to 4000% and carbon nanotubes with low levels of impurities have been obtained, pointing out the promoter character of Mo in the reaction. Therefore, the influence of Mo species has been studied in detail. The ana...

Excess enthalpies, densities, speeds of sound, and viscosities at (283.15, 298.15, and 313.15) K are reported for the binary mixture tetrahydropyran + 1-butanol. Excess molar volumes have been calculated from the densities. The deviations in both the speeds of sound and the absolute viscosities have also been estimated. All of the properties have b...