Fifty Years of Breakthrough Discoveries in Fluid Criticality

TL;DR

This paper reviews the groundbreaking discoveries in fluid critical phenomena over the past 50 years, highlighting how experimental findings on divergences in heat capacity and thermal conductivity shaped modern phase transition theories.

Contribution

It summarizes the historical experimental breakthroughs that challenged and advanced the understanding of critical phenomena in fluids, influencing modern scaling theories.

Findings

Discovered divergence of heat capacity at the critical point

Observed divergence of thermal conductivity near criticality

These singularities are universal for all fluids

Abstract

Fifty years ago two scientists, who celebrate their 80th birthdays in 2011, Alexander V. Voronel and Johannes V. Sengers performed breakthrough experiments that challenged the commonly accepted views on critical phenomena in fluids. Voronel discovered that the isochoric heat capacity of argon becomes infinite at the vapor-liquid critical point. Almost simultaneously, Sengers observed a similar anomaly for the thermal conductivity of near-critical carbon dioxide. The existence of these singularities was later proved to be universal for all fluids. These experiments had a profound effect on the development of the modern (scaling) theory of phase transitions, which is based on the diverging fluctuations of the order parameter. In particular, the discovery of the heat-capacity divergence at the critical point was a keystone for the formulation of static scaling theory, while the discovery of the divergence of the thermal conductivity played an important role in the formulation of dynamic scaling and mode-coupling theory. Moreover, owing to the discoveries made by Voronel and Sengers 50 years ago, critical phenomena in fluids have become an integral part of contemporary condensed-matter physics.