Raman spectra of graphene oxide and thermally reduced graphene oxide were analyzed in order to relate spectral parameters with the structural properties. The chemical composition of different graphene oxides was determined by organic elemental analysis, and the microstructure of nanocrystals was analyzed by X-ray diffraction. We find five reported bands (D, D′, G, D″, and D*) in the region between 1000 and 1800 cm–1 in all spectra. The band parameters such as position, intensity ratio, and width have been related with structural properties such as oxygen content, crystallinity, and disorder degree of GO and rGO platelets. An assessment of the validity of the Tuinstra–Koenig and Cuesta models was carried out by using the results obtained from the fit of the first-order spectra of graphene oxide derivatives at five functions: two Gaussian and three pseudo-Voigt peaks.

Raman spectra of graphene oxides (GOs) with different chemical compositions and synthesized by oxidation of distinct starting materials were analyzed to relate the spectral features to structural properties. The chemical compositions of different graphene oxides were determined by X-ray photoelectron spectroscopy (XPS), and nanoplatelets were characterized by zeta potential (ζ) and dynamic light scattering (DLS) measurements. The results indicated that the chemical composition, size, and superficial charge of the nanoplatelets depend on the starting material. We found five reported bands (D, D′, G, D″, and D*) in the first-order Raman spectrum and three bands (2D, D + D′, and 2D′) in the second-order Raman spectrum that successfully interpret the Raman spectra between 1000 and 3500 cm–1. Analysis of the bands allowed linear correlations to be found between the maximum positions of the 2D and D + D′ bands and between the relative intensities of the D and G bands (I D/I G) and the Csp2 percentage. Moreover, our results demonstrate that the relative intensities of the D′ and D bands are in excellent agreement with the theoretical correlations and allow the type of defects produced during oxidation, namely, vacancies or sp3 hybridation, to be related to the size of the graphene oxide sheets.

We study the effect of oxidative impurities on the properties of graphene oxide and on the graphene oxide Langmuir-Blodgett films (LB). The starting material was grupo Antolín nanofibers (GANF) and the oxidation process was a modified Hummers method to obtain highly oxidized graphene oxide. The purification procedure reported in this work eliminated oxidative impurities decreasing the thickness of the nanoplatelets. The purified material thus obtained presents an oxidation degree similar to that achieved by chemical reduction of the graphite oxide. The purified and non-purified graphene oxides were deposited onto silicon by means of a Langmuir-Blodgett (LB) methodology. The morphology of the LB films was analyzed by field emission scanning microscopy (FE-SEM) and micro-Raman spectroscopy. Our results show that the LB films built by transferring Langmuir monolayers at the liquid-expanded state of the purified material are constituted by close-packed and non-overlapped nanoplatelets. The isotherms of the Langmuir monolayer precursor of the LB films were interpreted according to the Volmer's model.

We synthesized graphene oxide sheets of different functionalization by oxidation of two different starting materials, graphite and GANF nanofibers, followed by purification based on alkaline washing. The chemical structure of graphene oxide materials was determined by X-ray photoelectron spectroscopy (XPS), and the nanoplatelets were characterized by ζ potential and dynamic light scattering (DLS) measurements. The XPS results indicated that the chemical structure depends on the starting material. Two different deposition methodologies, Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS), were employed to build the graphene oxide thin films. The film morphology was analyzed by scanning electron microscopy (SEM). The SEM images allow us to conclude that the LB methodology provides the highest coverage. This coverage is almost independent of the chemical composition of sheets. Conversely, the coverage obtained by the LS methodology increases with the percentage of C-O groups attached to sheets. Surface-pressure isotherms of these materials were interpreted according to the Volmer model.

We study the Brownian motion of probe particles embedded in a wormlike micellar fluid made of a zwitterionic surfactant N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (TDPS), sodium dodecyl sulfate (SDS), and salty water to get structural and dynamical information of the micellar network. The motion of the probe particles was tracked with diffusing wave spectroscopy, and the mean square displacement as a function of time for the particles was obtained. This allowed us to obtain the long-time diffusion coefficient for microspheres moving in the micellar network and the cage size where each particle is harmonically bound at short times in that network. The bulk mechanical susceptibility of the fluid determines the response of the probe particles excited by the thermal stochastic forces. As a consequence, the mean square displacement curves allowed us to calculate the elastic (storage) and the viscous (loss) moduli as a function of the frequency. From these curves, spanning a wide frequency range, we estimated the characteristic lengths as the mesh size, the entanglement length, the persistence length, and the contour length for micellar solutions of different zwitterionic surfactant concentration, surfactant ratio ([SDS]/[TDPS]), salt concentration, and temperature. Mesh size, entanglement length, and persistence length are almost insensitive to the change of these variables. In contrast, the contour length changes in an important way. The contour length becomes shorter as the temperature increases, and it presents a peak at a surfactant ratio of ∼0.50-0.55. When salt is added to the solution, the contour length presents a peak at a salt concentration of ∼0.225 M, and in some solutions, this length can reach values of ∼12 μm. Scission energies help us to understand why the contour length first increases and then decreases when salt is added.