ИСТИНА

Multiwavelength, scanning, and transient photothermal (PT, thermal lens and optoacoustic, OA) spectroscopy are used for the investigation and analysis (chemical analysis and the estimation of thermophysical properties and size) of nanodiamonds and fullerenes C60, C70 and their mixtures and their organic solutions and aqueous dispersions as promising ultra-dispersed materials having various applications. We used several approaches—thermal-lens and optoacoustic, transient (time-resolved) and stationary (thermal equilibrium) signals, spatial and time scanning—for estimating the size of clusters in aqueous fullerene and nanodiamonds solutions. The details of the experimental techniques will be provided. The data obtained have been compared to the results from other methods like dynamic laser scattering (DLS), differential scanning calorimetry (DSC) and electron microscopy. All the variants provide complementary information, and PT/OA spectroscopy can be used, along with the data from other methods, to characterize and monitor carbon nanomaterials and their aqueous dispersions. The estimation of the cluster size from two techniques—transient and imaging—giving concordant values and agreeing with DLS data is very invigorating. Although both techniques are currently unable to provide the information with enough precision due to undeveloped mathematical models, this direction of the unraveling photothermal spectroscopy shows very good outlooks. These data are supplemented by the estimation and determination of photothermal parameters (thermal conductivity, thermal expansion coefficient, heat capacity, thermal diffusivity, thermal effusivity, and density) for aqueous dispersions of nanodiamonds of various brands and fullerenes C60 and C70 of various concentrations by DSC, densitometry and other techniques. The possibilities to elucidate these parameters from photothermal experiments are discussed. The possibilities of PT/OA spectroscopy to determine submicrogram concentrations of nanodiamonds and fullerenes are shown. The advantages of these techniques over conventional spectroscopies due to much lower effect of light scattering and the signal enhancement in disperse solutions as well current limitations are discussed. The comparison of photothermal and fluorescence data is made. The necessity to develop robust models for transient and imaging photothermal techniques is outlined. Total scanning (TSF) fluorescence spectra of unmodified C60 and C70 in benzene, toluene, and n-hexane at room temperature are obtained and their peaks specific to each fullerene with intensities depending on the solvent are shown. The detection limits for fullerene C60 in n-hexane and C70 in benzene under the selected conditions are 20 nmol/L for C70 and 10 nmol/L for C60. The intensity and parameters of fluorescence dependence on the solvent and fullerene forms the approach for selective quantification of both fullerenes in their mixtures without separation by measuring TSF in a solvent enhancing the luminescence of one fullerene, while hindering another. The possibility of multiwavelength (multispectral) OPO-based PT/OA spectroscopy to complement the conventional spectrophotometric data on the nature of extinction spectra of aqueous nano-sized carbon dispersions is shown. The data are compared with conventional UV-visible spectroscopy. The proposed approach can be used (for nanodiamonds and fullerenes as well as dispersions of various nature) to distinguish between light absorption of these materials, light-scattering contribution, and photothermal effect to the overall picture of their properties.