Critical phenomena at
the single-particle level
Boiling and condensation are among the best recognized phase
transitions of condensed matter. Approaching the critical
point, a liquid becomes indistinguishable from its vapour,
the interfacial thickness diverges and the system is dominated
by long-wavelength density fluctuations. Long wavelength usually
means hundreds of particle diameters, but here we consider
the limits of this assumption, using a mesoscopic analogue
of simple liquids, a colloid-polymer mixture.
We simultaneously visualized both the colloidal particles
and near-critical density fluctuations, and reveal particle-level
images of the critical clusters and liquid-gas interface (see
above). Surprisingly, we find that critical scaling does not
break down until the correlation length approaches the size
of the constituent particles, where there is a smooth transition
to non-critical classical behaviour. Our results could provide
a framework for unifying the disparate particle and correlation
length scales, and bring new insight into the nature of the
liquid?gas interface and the limit of the critical regime.
Royall CP, Aarts, DGAL and Tanaka H, 'Bridging lengthscales in colloidal liquid-vapour interfaces: from near-critical divergence to single particles’, Nature Physics, 3 636-640 (2007).
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