Fröhlich Entropy of Nanoparticles: Investigation of Phases, Phase Transitions and Melting

We discuss the application of Fröhlich Entropy estimation as a dielectric thermodynamic tool to investigate phases, phase transitions, and melting processes in low-dimensional systems. In the first section we summarize selected results obtained on Gallium nanoparticles by means of an established powerful technique such as X-ray Absorption Spectroscopy (XAS). Firstly, we sketch the different phenomena that are associated with X-ray absorption by matter, and outline the theory of XAS. Then, we illustrate how the nanometric structure drives the phase transitions of Ga particles, as a function of their size. In particular, we will show how small nanoparticles (5 nm in radius) can be supercooled in the liquid state down to 90 K, and how larger nanoparticles (10 and 30 nm in radius) crystallize in the high pressure -Ga phase. These results are interpreted in terms of surface tension. Secondly, in the following section, Fröhlich Entropy estimation is discussed in relation to temperature-resolved dielectric measurements, extending the analysis beyond metallic nanoparticles. Specifically, this approach is shown to be useful for highlighting phase transitions, pretransitional phenomena, premelting, and melting processes, providing detailed information on the evolution of the state of order and phase stability, in excellent agreement with the data obtained by the XAS technique.