Frenkel’s entropy-exchange mechanism in monodisperse, nearly hard-sphere colloids: minimal perturbations to access fluid–crystal coexistence
Year: 2026
Type: article
Abstract: Entropically driven fluid–solid transitions in monodisperse, purely repulsive hard spheres (MPRHS) are well established in theory, simulation and experiment for atomic and colloidal systems. For MPRHS, however, coexistence is usually located via bulk free-energy calculations; the underlying microscopic balance between configurational and vibrational entropy is left implicit. Frenkel clarified this mechanism explicitly as an exchange of long-range configurational entropy for short-range vibrational entropy, but in the pristine MPRHS limit the nucleation barrier near coexistence is so high that phase separation is predicted only on astronomical time scales. Consistent with this, even unbiased simulations do not show spontaneous, equilibrium fluid–crystal coexistence; transient mixtures are mostly overtaken by a single phase; observed coexistence is still algorithmically driven. Nearly hard-sphere colloid experiments do observe fluid–crystal coexistence, but always in the presence of unavoidable triggers such as gravity and walls. We treat the hard-sphere phase diagram as settled and ask how the entropic exchange mechanism can be revealed in nearly hard-sphere colloidal simulations. We probe the mechanism on finite time scales by introducing minimal perturbations that trigger phase separation: small reductions in hardness that increase locally accessible free volume (and thus gently increase vibrational entropy), and 2 %–4 % distributed crystal seeds. These perturbations produce coexisting fluid and crystal domains with crystal fraction, phase envelope and osmotic pressure that, with systematically increasing particle hardness, approach the hard-sphere limit. These results demonstrate that slight enhancements to vibrational entropy provide a dynamically accessible route to realising the long-range/short-range entropy exchange required for phase separation.
Source: Journal of Fluid Mechanics
Institutions: University of Missouri, Eindhoven University of Technology
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $3,550
Awards: Track 4: Advanced CI Coordination Ecosystem: Monitoring and Measurement Services, G2299875479, G2888034965, G3185749182, Track 1: ACCESS Resource Allocations Marketplace and Platform Services (RAMPS), ACO: An Open CI Ecosystem to Advance Scientific Discovery (OpenCI), Track 3: COre National Ecosystem for CyberinfrasTructure (CONECT), G731264315, Track 2: Customized Multi-tier Assistance, Training, and Computational Help (MATCH) for End User ACCESS to CI, G878072758
OpenAlex ID: W7140042753