Electrostatic fluctuations in cavities within polar liquids and thermodynamics of polar solvation

We present the results of numerical simulations of the fluctuations of the electrostatic potential and electric field inside cavities created in the fluid of dipolar hard spheres. We found that the thermodynamics of polar solvation changes dramatically when the cavity size becomes about 4-5 times larger than the size of the liquid particle. The range of small cavities can be reasonably understood within the framework of current solvation models. On the contrary, the regime of large cavities is characterized by a significant softening of the cavity interface resulting in a decay of the fluctuation variances with the cavity size much faster than anticipated by both the continuum electrostatics and microscopic theories. For instance, the variance of the electrostatic potential at the cavity center decays with the cavity radius R0 approximately as 1R{0};{4-6} instead of the 1R{0} scaling expected from the standard electrostatics. Our results suggest that cores of nonpolar molecular assemblies in polar liquids lose solvation strength much faster than is traditionally anticipated.