The Casimir effect: from quantum to critical fluctuations

TL;DR

This paper reviews the Casimir effect, highlighting its quantum and critical fluctuation origins, and discusses recent theoretical and experimental advances in understanding the universal properties and tunability of the critical Casimir force in fluids.

Contribution

It provides a comprehensive overview of the universal features of the critical Casimir force and compares recent experimental measurements with theoretical predictions.

Findings

Theoretical models accurately predict the temperature dependence of the critical Casimir force.

Experimental measurements of the force match theoretical predictions with femto-Newton precision.

Surface treatments can effectively tune the strength and sign of the critical Casimir force.

Abstract

The Casimir effect in quantum electrodynamics (QED) is perhaps the best-known example of fluctuation-induced long-ranged force acting on objects (conducting plates) immersed in a fluctuating medium (quantum electromagnetic field in vacuum). A similar effect emerges in statistical physics, where the force acting, e.g., on colloidal particles immersed in a binary liquid mixture is affected by the classical thermal fluctuations occurring in the surrounding medium. The resulting Casimir-like force acquires universal features upon approaching a critical point of the medium and becomes long-ranged at criticality. In turn, this universality allows one to investigate theoretically the temperature dependence of the force via representative models and to stringently test the corresponding predictions in experiments. In contrast to QED, the Casimir force resulting from critical fluctuations can be easily tuned with respect to strength and sign by surface treatments and temperature control. We present some recent advances in the theoretical study of the universal properties of the critical Casimir force arising in thin films. The corresponding predictions compare very well with the experimental results obtained for wetting layers of various fluids. We discuss how the Casimir force between a colloidal particle and a planar wall immersed in a binary liquid mixture has been measured with femto-Newton accuracy, comparing these experimental results with the corresponding theoretical predictions.