Positron study of surface tension reduction in liquid alkane at high pressure of argon

Surface tension σ of sub-nanometric bubbles in n-nonadecane + argon system as a function of pressure was estimated using the positron lifetime spectroscopy. The surface tension is higher than for flat surface (due to negative bubble curvature). The coefficient (∂σ/∂p)_p=0 is negative but much smaller than for flat gas-liquid dividing surface. It can be explained by the lack of adsorbed argon layer on the bubble surface. In the narrow range of temperatures, where nonadecane melts by application of argon pressure, the concentration of argon in the liquid is found smaller than at higher temperatures and probably a kind of intermediate structure is formed. (paper)