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In this work we present a fabrication process for sculpturing wrinkled structures into soft polymers by thermal treatment of graphene flakes. This is accomplished by the imposition of a biaxial compressive stress field to the graphene flakes by controlled heating of graphene/polymer composites. The wrinkling patterns (amplitude, wavelength) are linearly related to the thickness of the graphene as in the case of a stiff film deposited on a compliant substrate. The orientation of the wrinkles is controlled by the geometry of the flakes, such as that long and narrow flakes exhibit perfectly parallel wrinkles perpendicular to the longer edge, while more equilateral specimens are wrinkled without any preferred orientation in the flake interior. Kelvin probe measurements showed that this type of wrinkling does not affect the surface potential of the graphene flakes. The universality of the technique is validated by sculpturing two different polymers, using mechanically exfoliated flakes as well as large graphene prepared by chemical vapor deposition. We thus demonstrate that the present approach is an excellent method for patterning the surface of soft matter in a number of applications with nanoscale features of lateral dimensions as low as ∼50 nm.

A methodology is presented here for deriving true experimental axial stress-strain curves in both tension and compression for monolayer graphene through the shift of the 2D Raman peak that is present in all graphitic materials. The principle behind this approach is the observation that the shift of the 2D wavenumber as a function of strain for different types of PAN based fibres is a linear function of their Young's moduli and, hence, the corresponding value of the shift of the 2D Raman peak over axial stress is, in fact, a constant. By moving across the length scales we show that this value is also valid at the nanoscale as it corresponds to the in plane breathing mode of graphene that is present in both PAN based fibres and monolayer graphene. Hence, the values of the shift of the 2D Raman peak can be easily converted to values of stress in the linear elastic region without the aid of modelling or the need to resort to cumbersome experimental procedures for obtaining the axial force transmitted to the material and the cross sectional area of the two dimensional membrane.

Strong polymer–MWCNT interactions in millimeter-high MWCNT/poly(vinyl alcohol) composite mats of vertically aligned tubes are reported. SEM and TEM imaging revealed extensive polymer sheathing to have occurred homogeneously over the nanotubes in the mats without influencing their morphology, alignment or physical characteristics. A 7- to 10-fold increase in the apparent nanotube diameter due to poly(vinyl alcohol) sheathing was measured. Thermogravimetric analysis showed that the composite mats were thermally more stable than the pure polymer. Differential scanning calorimetry results were compatible with a crystallinity increase of the polymer phase due to the presence of CNTs of the order of 18%. Potential applications of the produced composites include filters, components for sandwich panels and sensors.

The electrochemical modification of carbon nanotube films (buckypapers) in three different electrolytes consisting of two acids and a basic solvent at very low concentrations was studied. The electrolysis was performed at 1 A up to a maximum of 12 h. Four different characterization techniques have been employed for assessing the effectiveness of the proposed process. The results presented are very encouraging for the development of electrochemical oxidation as the main surface modification method for carbon nanotubes. It was found that the use of nitric acid electrolyte leads to scalable and controllable oxidation as compared to the basic electrolyte which was also effective but appeared to damage the graphitic structure of nanotubes during longer treatments.

The effect of oxidation on the structural integrity of multiwalled carbon nanotubes through acidic (nitric acid and a mixture of sulfuric acid and hydrogen peroxide) and basic (ammonium hydroxide/hydrogen peroxide) agents has been studied. In order to purify the as-received material, a non-oxidative treatment (with hydrochloric acid) was also applied. Electron microscopy and thermogravimetric analysis clearly revealed that the nitric acid-treated material under reflux conditions suffered the highest degree of degradation, such as, nanotube shortening and additional defect generation in the graphitic network. Basic oxidative treatment led to the complete removal of amorphous carbon and metal oxide impurities but the structural integrity was found to be intact. X-ray photoelectron spectroscopy was employed to confirm the different functionalities produced for each oxidation agent, whereas titration measurements determined the relative concentration of carboxylic functions onto the graphitic surface. Moreover, a general relationship between the chemical treatment and the amount of non-graphitic carbon was established by means of Raman spectroscopy measurements. The possibility of controlling the required amount of functionality, carboxylic and hydroxyl, via these oxidation procedures is discussed.