Strongly metastable assemblies of particles at liquid interfaces.

Area of Science:

• Physics
• Materials Science
• Colloid Science

Background:

• Self-assembly of floating particles into ordered structures is a fundamental phenomenon.
• Ideally, rafts of identical floating spheres or cylinders should form closed-packed arrangements.
• Observed rafts frequently display significant defects, deviating from ideal packing.

Purpose of the Study:

• To investigate the mechanisms causing defects in self-assembled rafts of floating particles.
• To explore the role of lateral liquid bridges and contact angle hysteresis in raft formation.
• To demonstrate the potential of capillary forces for creating non-equilibrium 2D aggregates.

Main Methods:

• Theoretical analysis of capillary forces between floating particles.
• Experimental observation of particle raft self-assembly.
• Investigation of the influence of contact angle hysteresis on particle rotation and arrangement.

Main Results:

• Identified that the combination of lateral liquid bridges and contact angle hysteresis restricts particle rotation, leading to imperfect raft structures.
• Demonstrated that these capillary interactions are responsible for the observed defects in rafts.
• Showcased the ability to engineer persistent 2D aggregates far from equilibrium by exploiting capillary bonds.

Conclusions:

• Capillary interactions, specifically liquid bridges and contact angle hysteresis, are key drivers of defect formation in floating particle rafts.
• These forces can be controllably utilized to create stable, non-equilibrium 2D structures.
• Understanding these mechanisms opens avenues for designing novel self-assembled materials.