Frozen Cheerios effect: Particle-particle interaction induced by an advancing solidification front

TL;DR

This study investigates how thermal conductivity differences influence particle interactions during water freezing, revealing a new 'frozen Cheerios effect' driven by thermal and interface dynamics, with implications for material science and cryopreservation.

Contribution

The paper introduces the concept of the frozen Cheerios effect, demonstrating how thermal conductivity mismatch affects particle clustering during solidification, supported by experimental and theoretical analysis.

Findings

Particles more conductive than water attract and cluster during freezing.

Less conductive particles tend to separate, preventing clustering.

Interaction strength depends on solidification front velocity.

Abstract

Particles at liquid interfaces have the tendency to cluster due to capillary forces competing with gravitational buoyancy (i.e., normal to the distorted free surface). This is known as the Cheerios effect. Here we experimentally and theoretically study the interaction between two submerged particles near an advancing water-ice interface during the freezing process. Particles that are thermally more conductive than water are observed to attract each other and form clusters once frozen. We call this feature the frozen Cheerios effect, where interactions are driven by alterations to the direction of the experienced repelling force (i.e., normal to the distorted isotherm). On the other hand, particles less conductive than water separate, highlighting the importance of thermal conduction during freezing. Based on existing models for single particle trapping in ice, we develop an understanding of multiple particle interaction. We find that the overall efficacy of the particle-particle interaction critically depends on the solidification front velocity. Our theory explains why the thermal conductivity mismatch between the particles and water dictates the attractive/repulsive nature of the particle-particle interaction.