Lengthscale-Dependent Solvation and Density Fluctuations in n-Octane

Much attention has been focused on the solvation and density fluctuations in water over the past decade. These studies have brought to light interesting physical features of solvation in condensed media, especially the dependence of solvation on the solute lengthscale, which may be general to many fluids. Here, we focus on the lengthscale-dependent solvation and density fluctuations in n-octane, a simple organic liquid. Using extensive molecular simulations, we show a crossover in the solvation of solvophobic solutes with increasing size in n-octane, with the specifics of the crossover depending on the shape of the solute. Large lengthscale solvation, which is dominated by interface formation, emerges over subnanoscopic lengthscales. The crossover in n-octane occurs at smaller lengthscales than that in water. We connect the lengthscale of crossover to the range of attractive interactions in the fluid. The onset of the crossover is accompanied by the emergence of non-Gaussian tails in density fluctuations in solute shaped observation volumes. Simulations over a range of temperatures highlight a corresponding thermodynamic crossover in solvation. Qualitative similarities between lengthscale-dependent solvation in water, n-octane, and Lennard-Jones fluids highlight the generality of the underlying physics of solvation.

@article{wu2015lengthscale,
  title   = {Lengthscale-Dependent Solvation and Density Fluctuations in n-Octane},
  author  = {Wu, Eugene and Garde, Shekhar},
  journal = {J. Phys. Chem. B},
  volume  = {119},
  number  = {29},
  pages   = {9287--9294},
  year    = {2015},
  doi     = {10.1021/jp509912v}
}