Approach to the Assessment of Size-Dependent Thermal Properties of Disperse Solutions: Time-Resolved Photothermal Lensing of Aqueous Pristine Fullerenes C-60 and C-70

摘要

An approach is proposed for assessment of the thermal properties of aqueous pristine fullerene C-60 and C-70 dispersions (AFDs) at the level of 10(-7)-10(-5)mol L-1 by photothermal (thermal-lens) spectroscopy for their application in medicine and technology. Along with relevant size characterization techniques differential scanning calorimetry (DSC) with the Gibbs Kelvin equation and dynamic light scattering (DLS) techniques this approach provides an estimation of the size-dependent thermal properties of disperse solutions thermal diffusivity, thermal effusivity [thermal inertia], and thermal conductivity. The values for AFDs under the conditions of the attained thermal equilibrium show good precision, and the cluster size estimations agree with the reference methods. The reconstruction of the thermal-lens characteristic time over the course of the blooming of the thermal-lens effect reveals a short increase in the apparent thermal diffusivity. This is accounted for by nonequilibrium heat transfer within fullerene clusters upon initial laser heating, which is supported by the independent estimations from widespread methods like high-resolution transmission electron microscopy, DLS, and DSC. Thermophysical parameters of the disperse phase estimated from transient thermal lensing are as follows: thermal diffusivity, 1.6-2.0 x 10(-7) m(2) s(-1) depending on fullerene concentration and up to 3.5 X 10(-7) m(2) s(-1), more than 2-fold higher than for water; thermal effusivity, 6.7 X 10(2) J m(-2) K-1 s(-1/2), three times lower than for water.