  Liquid-liquid transition (LLT) in single-component liquids is one of the most
mysterious phenomena in condensed matter. So far this problem has attracted
attention mainly from the purely scientific viewpoint. Here we report the first
experimental study on an impact of surface nano-structuring on LLT by using a
surface treatment called rubbing, which is the key technology for the
production of liquid crystal displays. We find that such a rubbing treatment
has a significant impact on the kinetics of liquid-liquid transition (LLT) of
an isotropic molecular liquid, triphenyl phosphite. For a liquid confined
between rubbed surfaces, surface-induced barrier-less formation of the liquid
II phase is observed even in a metastable state, where there should be a
barrier for nucleation of the liquid II phase in bulk. Thus, surface rubbing of
substrates not only changes the ordering behavior, but also accelerates the
kinetics significantly. This spatio-temporal pattern modulation of LLT can be
explained by a wedge filling transition and the resulting drastic reduction of
the nucleation barrier. However, this effect completely disappears in the
unstable (spinodal) regime, indicating the absence of the activation barrier
even for bulk LLT. This confirms the presence of nucleation-growth-type and
spinodal-decomposition-type LLT, supporting that LLT is truly a first-order
transition with criticality. Our finding also opens up a new way to control the
kinetics of LLT of a liquid confined in a solid cell by structuring its surface
on a mesoscopic lengthscale, which may contribute to making LLT useful for
micro-fluidics and other industrial applications.
