CONFINED FLUID 3He: THERMODYNAMIC PROPERTIES AND CRITICAL BEHAVIOR IN QUASI-ONE DIMENSION

A variational approach has been used to study the behavior of fluid( 3)He confined in a single-wall carbon nanotube at finite temperature (1 - 4 K). We have calculated the energy of system by employing the variational method based on the quantum cluster expansion of the energy. Then, some thermodynamic properties such as entropy, free energy, equation of state, compressibility and specific heat have been investigated. This study has been done for a density range of 0.1 - 1.0 nm (-1)and three different carbon nanotube radii, R = 0.3, 0.48 and 0.8 nm. Our result for the equation of state shows a liquid-gas second order phase transition for this confined system at a density and temperature which depend on the nano-tube radius. The critical behavior of this system has been studied, and the relevant critical exponents have been verified by Griffiths inequality. The remarkable point of this study is the low density and pressure of transition point in comparison with no confined case. This phenomenon is differentiated from the strong adsorption of( 3)He atoms by the carbon nanotube wall.