  Nanoscale topographic features of solid surfaces can induce complex
metastable behavior in colloidal and multiphase systems. Recent studies on
single microparticle adsorption at liquid interfaces have reported a crossover
from fast capillary driven dynamics to extremely slow kinetic regimes that can
require up to several hours or days to attain thermodynamic equilibrium. The
observed kinetic regime resembling physical ageing in glassy materials has been
attributed to unobserved surface features with dimensions on the order of a few
nanometers. In this work, we study the spontaneous spreading of water droplets
immersed in oil and report an unexpectedly slow kinetic regime not described by
previous spreading models. We can quantitatively describe the observed regime
crossover and spreading rate in the late kinetic regime with an analytical
model considering the presence of periodic metastable states induced by
nanoscale topographic features (characteristic area ~4 nm^2, height ~1 nm)
observed via atomic force microscopy. The analytical model proposed in this
work reveals that certain combinations of droplet volume and nanoscale
topographic parameters can significantly hinder or promote wetting processes
such as spreading, wicking, and imbibition.

Soft Condensed Matter