ИСТИНА

Photothermal (PTS) and photoacoustic (PAS) spectroscopies were used for characterizing nanodiamond (ND) sols and fullerene dispersions in aqueous and organic media. The motivation of this study is the fact that many relevant properties of these carbon species as materials, nanofluids, or biolabels depend on their production and purification technologies, and it is strongly necessary to know both the concentration and distribution and their primary particle and aggregate sizes. We used PTS/PAS in multiwavelength, transient, and scanning modes and in meso- and microscopic scales for physicochemical analysis and the estimation of thermophysical properties of aqueous fullerene dispersions (AFDs) and ND. The schematics and details of PTS/PAS measurements will be provided. Steady-state and transient techniques of photothermal-lens (thermal-lens) spectrometry (TLS) are used to characterize concentrational parameters of AFDs at the level of 10–8–10–5 mol L–1; to assess thermophysical properties of AFDs; and to estimate the features of heat transfer due to the cluster formation in AFDs. The detection limit of fullerenes in AFDs by PTS for C60 and C70 are ca. 100 ng/mL, which are 20-fold lower than for conventional spectrophotometry. An approach for the thermophysical characterization of AFDs of C60 and C70 and ND by TLS by the reconstruction of thermal-lens characteristic time over the course of the development of thermal-lens effect (transient curves) is proposed. Along with relevant size-characterization techniques, this approach was applied for thermal diffusivity, thermal effusivity [thermal inertia], and thermal conductivity of AFDs with heat capacity and density from differential scanning calorimetry and densitometry. The data from thermal lensing corresponding to thermal equilibrium show good precision and are in agreement with literature data for water. These parameters were measured in dynamic (time-resolved transient response profiles of thermal-lens signals) and batch (amplitude) modes of PTS. Several PTS methods and their applicability towards this aim will be compared. An anomalous short-time (100-400 ms scale) increase in the thermal diffusivity upon cw chopped laser-induced heating for both AFDs (10–6–10–5 mol L–1) up to 30% was observed in time-resolved thermal lensing, which is accounted for non-equilibrium heat transfer within fullerene clusters upon initial heating followed by the heat transfer to the bulk of the solvent. The thermal diffusivity of the dispersed particles is estimated as twofold higher than for water, which agrees with the thermophysical parameters of bulk fullerenes. The advantages and drawbacks of the proposed approach are discussed. The whole behavior of the thermophysical parameters in AFDs obtained from thermal lensing agree with the features of prepared AFDs obtained from electron microscopy, differential scanning calorimetry (with the Gibbs–Kelvin equation), and dynamic laser scattering techniques. Key thermophysical properties of ND dispersions (from 20 trademarks from various manufacturers) as nanofluids—thermal diffusivity, thermal effusivity, and thermal conductivity—were estimated from PTS (thermal-lens) data using the same approach, and their values were compared with pure solvents and other types of nanofluids. The same short-time increase in thermal diffusivity is observed and it is in in agreement with the previous data on steady-state thermal lensing. The estimation of ND concentrations at subnanogram amounts by PTS is shown. Extinction spectra of ND aqueous dispersions by conventional absorption spectroscopy and PAS differ significantly, and the contributions from absorption and scattering were estimated by their comparison. PTS/PAS multispectral data were correlated with the results from other methods: DSC, dynamic laser scattering (DLS), X-ray diffraction, and UV-spectroscopy. The estimation of the cluster size from two techniques—transient and imaging PTS–results in concordant values and agree with DLS data, which is rather invigorating for further investigations.