War and peace between electrostatic and van der Walls forces regulate translational and rotational diffusion

In the Stokes-Einstein picture, diffusion of a Brownian particle or a molecule in a liquid solvent is caused by unbalanced fluctuations of osmotic forces on different sides of the particle. When the particle carries a charge or a higher multipolar moment, this picture is amended by fluctuations of electrostatic forces producing dielectric friction. Dielectric friction slows down both the translational and rotational diffusion. While this picture is well established and is physically sound, standard theories grossly overestimate the magnitude of dielectric friction for small dipolar solutes and larger colloidal particles, such as proteins. Motivated by recent simulation studies, this Perspective discusses the interplay between osmotic (van der Waals) and electrostatic forces in promoting molecular and colloidal diffusion. Much can be learned about microscopic friction mechanisms from statistical and dynamical correlations between osmotic and electrostatic forces. Published under an exclusive license by AIP Publishing.

Automated summary

In the Stokes-Einstein picture, diffusion is caused by fluctuations of osmotic forces on different sides of the particle. The presence of charge or higher multipolar moments results in dielectric friction which slows down diffusion. However, standard theories overestimate the magnitude of dielectric friction in small solutes and larger colloidal particles.