Raquel Verdejo

Graphene filled polymer nanocomposites

Graphene has attracted the attention of a growing number of scientists from several disciplines due to its remarkable physical properties and chemical functionalisation capabilities. This review presents an overview of graphene/polymer nanocomposites discussing preparation, properties and potential applications. The challenges and outlook of these emerging polymer nanocomposites are also discussed.

Functionalized graphene sheet filled silicone foam nanocomposites

In this article we report the successful manufacture of a novel functionalized graphene sheet (FGS)/silicone porous nanocomposite. Both the cellular microstructure and the properties of the porous nanocomposite were investigated in detail. The thermal properties show great stability and heat dissipation efficiency, highlighting their potential in applications with intense thermal requirements. Additionally, compression measurements indicate that there was a favourable interaction between the graphene nanosheets and the polymer.

Removal of oxidation debris from multi-walled carbon nanotubes

Conventional liquid phase oxidation of multiwall carbon nanotubes (MWCNTs) using concentrated acids generates contaminating debris that should be removed using aqueous base before further reaction.

Use of butylamine modified graphene sheets in polymer solar cells

We describe a facile method to use soluble chemically derived few-layer graphene sheets (GSs) as part of a transparent electrode for the preparation of polymer solar cells. Chemically functionalized GSs were obtained by first covalently attaching fluorine and then exposing the obtained fluorinated graphene sheets to an aliphatic amine at room temperature. Scanning electron microscopy, atomic force microscopy and UV-Vis analyses confirmed that transparent graphene sheets with an average thickness of 0.7–0.9 nm had been obtained. Their application in a polymer solar cell is demonstrated. Such functionalized graphene, which is cheap and easily prepared, is expected to be used as hole acceptor material in polymer photovoltaic applications.

Thermal conductivity of carbon nanotubes and graphene in epoxy nanofluids and nanocomposites

AbstractWe employed an easy and direct method to measure the thermal conductivity of epoxy in the liquid (nanofluid) and solid (nanocomposite) states using both rodlike and platelet-like carbon-based nanostructures. Comparing the experimental results with the theoretical model, an anomalous enhancement was obtained with multiwall carbon nanotubes, probably due to their layered structure and lowest surface resistance. Puzzling results for functionalized graphene sheet nanocomposites suggest that phonon coupling of the vibrational modes of the graphene and of the polymeric matrix plays a dominant role on the thermal conductivities of the liquid and solid states. PACS: 74.25.fc; 81.05.Qk; 81.07.Pr.

Functionalised graphene sheets as effective high dielectric constant fillers

A new functionalised graphene sheet (FGS) filled poly(dimethyl)siloxane insulator nanocomposite has been developed with high dielectric constant, making it well suited for applications in flexible electronics. The dielectric permittivity increased tenfold at 10 Hz and 2 wt.% FGS, while preserving low dielectric losses and good mechanical properties. The presence of functional groups on the graphene sheet surface improved the compatibility nanofiller/polymer at the interface, reducing the polarisation process. This study demonstrates that functionalised graphene sheets are ideal nanofillers for the development of new polymer composites with high dielectric constant values.PACS: 78.20.Ci, 72.80.Tm, 62.23.Kn

Poly(lactic acid)/natural rubber/cellulose nanocrystal bionanocomposites Part I. Processing and morphology

PLA/NR/cellulose nanowhisker composites were prepared using three types of cellulose nanocrystals (CNC), i.e. unmodified CNC obtained from acid hydrolysis of microcrystalline cellulose and two surface modified CNC. The two modification reactions, consisting on the grafting of long alkyl chains and of PLA chains onto the cellulose nanocrystals were carried out in order to facilitate the incorporation of the nanocrystals in the PLA/NR blend. A novel processing method was optimized combining solvent casting and extrusion in order to obtain a homogeneous dispersion of the nanofillers in the blend. The CNC modifications determined their location in the PLA/NR blend and influenced its morphology.

Carbon nanotube-enhanced polyurethane scaffolds fabricated by thermally induced phase separation

Nanocomposite foams are an attractive prospect in a number of fields including biomedical science, catalysis and filtration. In biomedical engineering, porous nanocomposite scaffolds can potentially mimic aspects of the nanoscale architecture of the extra-cellular matrix, as well as enhance the mechanical properties required for successful weight-bearing implants. Thermoplastic polyurethane–multi-walled carbon nanotubes (CNTs) foams were manufactured by thermally induced phase separation (TIPS). TIPS proved to be a successful manufacturing route to three-dimensional, highly porous polymers containing well-dispersed CNTs. Some CNTs are trapped perpendicular to the pore surface creating a rough, nanotextured surface. The surface character of the nanocomposites became more acidic with increasing loading fraction of oxidised CNTs. However, due to the heterogeneity of the nanocomposite surface, its wetting behaviour was not affected. CNT incorporation significantly improved the compression strength and stiffness of the nanocomposite scaffold. The biological properties of these scaffolds were studied in vitro and revealed that increasing MWNT loading fraction did not cause osteoblast cytotoxicity or detrimental effects on osteoblast differentiation or mineralisation. However, osteoblast production of the potent angiogenic factor VEGF (vascular endothelial growth factor) increased in proportion to CNT loading (after 3 days in culture), revealing the potential of the nanocomposite scaffolds to influence cellular behaviour.

Poly(lactic acid)/natural rubber/cellulose nanocrystal bionanocomposites. Part II: properties evaluation.

The crystallization, mechanical and biodegradation properties of poly(lactic acid)/natural rubber/cellulose nanocrystals (CNC) bionanocomposites were evaluated. Three types of CNC were used in this study, one unmodified (CNC), long alkyl chain grafted CNC (C18-g-CNC) and PLA grafted CNC (PLA-g-CNC). The CNC modifications determined the affinity of the nanocrystals toward the polymers and reflected on the ultimate properties. Interestingly, PLA-g-CNC acted as a nucleating agent for the PLA matrix in the bio-based PLA/NR blend. Good mechanical properties were reported, as the bionanocomposites maintained a high elongation at break for a concentration up to 3 wt.% of cellulose nanocrystals. Moreover, the disintegration study confirmed that the materials completely disintegrated after one month in compost.

Towards materials with enhanced electro-mechanical response: CaCu3Ti4O12-polydimethylsiloxane composites

We describe a straightforward production pathway of polymer matrix composites with increased dielectric constant for dielectric elastomer actuators (DEAs). Up to date, the approach of using composites made of high dielectric constant ceramics and insulating polymers has not evidenced any improvement in the performance of DEA devices, mainly as a consequence of the ferroelectric nature of the employed ceramics. We propose here an unexplored alternative to these traditional fillers, introducing calcium copper titanate (CCTO) CaCu3Ti4O12, which has a giant dielectric constant making it very suitable for capacitive applications. All CCTO–polydimethylsiloxane (PDMS) composites developed display an improved electro-mechanical performance. The largest actuation improvement was achieved for the composite with 5.1 vol% of CCTO, having an increment in the actuation strain of about 100% together with a reduction of 25% in the electric field compared to the raw PDMS matrix.