Direct measurement of the Orderphobic Effect

TL;DR

This paper experimentally demonstrates the Orderphobic Effect, a fluctuation-induced force near first-order phase transitions, showing how solutes can nucleate disordered phases and attract each other in non-equilibrium systems.

Contribution

It provides the first quantitative measurement of the Orderphobic Effect in a driven granular fluid, establishing its universality and potential for controlling self-assembly.

Findings

Confirmed the existence of the Orderphobic Effect in a non-equilibrium system.

Quantified the attractive force between solutes near phase coexistence.

Demonstrated the effect's universality as an analog to the Critical Casimir Effect.

Abstract

Fluctuation-induced forces, such as the Critical Casimir Effect (CCE), are fundamental mechanisms driving organization and self-assembly near second-order phase transitions. The existence of a comparable, universal force for systems undergoing a first-order transition has remained an unresolved fundamental question. The proposed Orderphobic Effect is one such potential mechanism. It arises from minimisation of the interfacial free energy between solutes that locally nucleate a disordered phase. Here, we report the first experimental demonstration and quantitative measurement of the Orderphobic Effect. Using a driven, non-equilibrium quasi-2D granular fluid undergoing a first-order order-disorder transition, we show that specifically designed solutes in an ordered phase nucleate a coexisting ``bubble'' of the disordered phase. By analysing its capillary fluctuations, we confirm that this phenomenon occurs due to the proximity to phase-coexistence, and we directly quantify the attractive force by measuring the interaction free energy between solutes. The observation of this general fluctuation-mediated force in a non-equilibrium steady state strongly supports its claimed universality. Our work establishes the Orderphobic Effect as the first-order equivalent to the CCE, providing a new, general route for controlling self-assembly and aggregation in soft matter and non-equilibrium systems.