Surface tension of sulfur nanoparticles as determined from homogeneous nucleation experiments

Abstract

The surface tension of sulfur nanodrops (critical nuclei) is determined from the homogeneous nucleation investigation results. To this end a laminar flow nucleation chamber is used. The aerosol concentration and size distribution are monitored at the chamber outlet by the diffusion battery and gravitational sedimentation techniques. The nucleation volume is evaluated by the “supersaturation cut-off” method. The region of aerosol formation is localized by the 90° light scattering approach. The nucleation rate is determined experimentally from the outlet aerosol concentration and the nucleation volume to be Iexp≈2.3×107cm−3s−1 at nucleation temperature Texp≈310K and the total supersaturation (total vapor pressure to saturated vapor pressure ratio) sexp=1.9×103. Using the rigorous formula for the nucleation rate (taking the translation-rotation correction factor into account) the surface tension of critical nucleus and its radius of the surface of tension is determined from Iexp, Texp and sexp to be σexp=72.11mN/m and RS,exp=0.980nm, respectively. To calculate the critical nucleus surface tension more exactly a numerical simulation of vapor to particles conversion is carried out. As a result the nucleation rate is determined to be in the range 3×103−2×108cm−3s−1 for the supersaturation of S8 species to be in the range 4000–380 and nucleation temperature 300–350K. The surface tension σS of the sulfur critical nucleus is calculated to be in the range 67–75mN/m for the radius of the surface of tension 1.08–0.95nm. These values of surface tension exceed by 2–5% the surface tension σ∞ for flat sulfur interface. Such a small deviation of σS from σ∞ is in agreement with the author׳s assumption that the surface tension for non-metal elements is essentially independent of curvature as in contrast to the metal nanoparticles. The comparison with the nanodrop surface tension for other elements makes it possible to conclude that the larger is the group number in the Periodic Table the less is the absolute value of difference between the surface tension of critical nucleus and that of the flat surface.