Nonequilibrium ordering dynamics of confined soft alginate hydrogel colloids driven by time-evolving electrostatic...

Area of Science:

• Colloid and Surface Science
• Soft Matter Physics
• Materials Science

Background:

• Understanding structure formation in nonequilibrium colloidal systems is challenging due to limited experimental tools.
• Electrostatic interactions play a crucial role in colloidal self-assembly.

Purpose of the Study:

• To create a controllable model system for studying evolving repulsive interactions and colloidal ordering.
• To investigate the transition from disordered to ordered states driven by tunable electrostatic forces.

Main Methods:

• Utilized alginate hydrogel colloids confined within cyclohexyl bromide (CHB) emulsion droplets.
• Employed barium ions (Ba²⁺) to progressively increase droplet surface charge and induce crosslinking.
• Combined quantitative imaging with Brownian dynamics simulations to analyze structural evolution and interaction parameters.

Main Results:

• Demonstrated that increasing electrostatic repulsion, coupled with buoyancy-driven compaction, leads to the formation of quasi-two-dimensional layers.
• Observed a transition from a disordered state to a hexagonally ordered structure as repulsion strengthened.
• Quantified the effective Debye screening length (≈2.5-3 μm) and the critical interaction parameter (≈117-149) for ordering.

Conclusions:

• The alginate-CHB system provides a robust platform for probing charge-regulated colloidal ordering under confinement.
• The observed reversible disordered-order behavior highlights the dynamic nature of this nonequilibrium system.
• This model system offers new avenues for studying fundamental principles of self-assembly in complex fluids.