Partial Molar Volume and Solvation Structure of Naphthalene in Supercritical Carbon Dioxide:  A Monte Carlo Simulation Study

Abstract

Monte Carlo simulations were used to investigate the solvation of naphthalene in supercritical carbon dioxide at a temperature of 308.38 K just above the solvent's critical temperature and at pressures of 74.6, 79.7, 87.8, and 310.2 bar covering a range from just below to far above the solvent's critical pressure and at a slightly elevated temperature of 318.15 K and a pressure of 93.0 bar. The Monte Carlo simulations were carried out in the isobaric−isothermal ensemble and employed the transferable potentials for phase equilibria (TraPPE) force field. Systems containing 2000 carbon dioxide molecules and from 0 to 4 solute molecules were used for all five state points, and additional simulations with 16 000 solvent molecules were carried out at the lower temperature and p = 79.7 bar. In agreement with experiment, the simulations yield large, negative partial molar volumes of naphthalene near the critical pressure at 79.7 bar, with values of −4340 ± 750 and −3400 ± 620 cm3 mol-1 for the 2000 and 16 000 molecule systems, respectively. Structural analysis through radial distribution functions and the corresponding number integrals yields good agreement with neutron diffraction data and shows evidence for a long-range density enhancement around solutes but lacking any specific solute−solvent clustering. Solvatochromic shifts estimated from the local solvent structure correlate well with the experimental data over the entire pressure range.

Widom Delta of Supercritical Gas–Liquid Coexistence

“…Next, we test the possible link between the coexistence and anomalous behavior of the SCF. One such hallmark of supercritical solutions is the divergence of the solute's partial molar volume (PMV) close to the critical point [20][21][22][23][24]. In particular, the PMV of attractive solutes is known to exhibit largely negative PMV, i.e.…”

Monte Carlo simulations of phase behavior and microscopic structure for supercritical CO2 and thiophene mixtures

“…Molecular simulation has previously been applied successfully to determine solubility of naphthalene, benzoic acid, hydroxybenzoic acid, etc. in ScCO 2 [22][23][24][25]. Here, we attempt to study the thermodynamic properties in solution mixtures of thiophene and ScCO 2 and provide molecular level insights on the interactions between the thiophene and CO 2 in supercritical phase.…”

Modeling Solvation in Supercritical CO2

“…[71] As equential molecular dynamics (MD) andq uantum mechanics approach was used by Millot et al to compute the UV/Vis spectrum of organic dyes, [72] and more recently Born-Oppenheimer MD simulations were performed by Canuto's group to study the electronic spectrum of para-nitroaniline. [73,74] The organization of the solvent around the solute and its influence on the solution structural and dynamic properties were investigated by means of MD for small solutes, [75][76][77][78][79][80][81][82][83][84] polymers [85,86] and proteins, [87] and passivated gold nanoparticles. [88] Some work based on Car-Parrinello MD was also performed.…”