ULTRASONIC DISPERSION OF FULLERENE C<sub>60</sub> IN THE AQUEOUS SOLUTIONS OF MIXTURES OF IONIC AND NON-IONIC SURFACTANTS. PART 1
When obtaining the fullerene C60 dispersions through ultrasonication, surfactants are promising as dispersing and stabilizing agents. Preparing the mixtures of ionic and nonionic surfactants, which differ in their critical micelle concentrations, hydrophilic-lipophilic balances, molecular weights, and the mechanisms of stabilizing the carbon nanoparticles, as well as identifying the most efficient mixtures with the increased total dispersing and stabilizing action, can be one of the ways to solve the problem of aggregating nanoparticles and to obtain the C60 dispersions with the desired colloidal properties. This study was aimed at obtaining and investigating the efficient surfactant mixtures for increasing the dispersed phase content during ultrasonic dispersion processes and to enhance the stability of the fullerene C60 dispersions. The object of our studies was the electric arc synthesis fullerene C60 with a purity of above 99.5%. Mixtures of ethoxylated alkylphenols (EO AF) with different degrees of ethoxylation (n = 8, 10, 12) were used, as well as mixtures of EO AF n = 12 with sodium dodecyl sulfate (SDS) and sodium dodecyl benzenesulfonate (SDBS). It is shown that increase in the average degree of ethoxylation of EO AF n = 8-12 contributes to increasing the optical density of dispersions under ultrasonic action and the system stability. The optical density of dispersions, the average hydrodynamic diameter, and the electrokinetic potential of fullerene particles were found using absorption spectroscopy and dynamic and electrophoretic light scattering. The concentration regions of obtaining the synergic mixtures of surfactants were identified using surface tension measurements. It is found that the highest dispersing and stabilizing effects are manifested by the mixture of ethoxylated isononyl phenols with the average ethoxylation degrees of n=8 and n=12 and the mol fraction of n=12 equaling to 0.4. As compared to the dispersions obtained without involving any surfactants, we have managed to reduce the particle sizes by 1.8 times and the polydispersity by 1.9 times, having simultaneously increased the optical density and stability of the systems by 11.7 and 2.8 times, respectively. The findings of these studies can be used in the preparation of fullerene C60 dispersions for biochemical and biomedical research and in doping the composite materials.