Role of polydispersity in anomalous interactions in electrostatically levitated colloidal systems

Area of Science:

• Colloid and Surface Science
• Computational Physics
• Statistical Mechanics

Background:

• Extracting interparticle potentials from experimental data is crucial for understanding colloidal systems.
• Existing inverse analysis methods are typically developed for monodisperse (uniform size) particles.
• Real-world colloidal systems often exhibit polydispersity (a range of particle sizes).

Purpose of the Study:

• To investigate the impact of particle size polydispersity on inverse analyses used to determine interparticle potentials.
• To evaluate the performance of inverse Ornstein-Zernike and inverse Monte Carlo methods with polydisperse colloids.
• To provide a framework for interpreting experimental data from polydisperse interfacial colloidal systems.

Main Methods:

• Generated 3D equilibrium configurations of polydisperse colloidal particles using forward Monte Carlo simulations.
• Particles were confined by gravity near a surface and stabilized by electrostatic potentials.
• Applied inverse Ornstein-Zernike and inverse Monte Carlo analyses to simulated distribution functions.

Main Results:

• Both inverse methods accurately recovered potentials for monodisperse systems.
• Significant deviations and failures were observed when applying methods to polydisperse systems.
• Observed artifacts include softened repulsion, apparent attraction, and particle overlaps, mirroring experimental findings.

Conclusions:

• Particle polydispersity significantly compromises the accuracy of standard inverse analyses for extracting interparticle potentials.
• The study highlights specific signatures of polydispersity that can be misinterpreted in experimental data.
• Results offer a basis for more objective interpretation and resolution of polydispersity effects in optical microscopy of colloidal ensembles.