A colloidal model system with an interaction tunable from hard sphere to soft and dipolar.

Area of Science:

• Condensed matter physics
• Colloidal science
• Soft matter physics

Background:

• Micrometre-sized spheres are crucial model systems for studying condensed matter phenomena like glass transitions.
• Quantitative real-space studies on crystal melting and long-range repulsive potentials are lacking.

Purpose of the Study:

• To create a colloidal suspension model for real-space studies of crystal melting.
• To investigate systems with tunable long-range repulsive potentials and anisotropic interactions.
• To explore rich phase behavior in colloidal systems.

Main Methods:

• Developed a charge- and sterically stabilized poly(methyl methacrylate) colloidal suspension.
• Utilized confocal microscopy for real-space observations.
• Controlled interaction potential by varying solvent salt concentration and applying external electric fields.

Main Results:

• Demonstrated independent control over repulsive range and anisotropic interparticle interactions.
• Observed rich phase behavior, including unusual colloidal crystalline phases.
• Showcased electric field as a tunable parameter for controlling interactions and enabling pseudo-thermodynamic temperature switching for melting studies.

Conclusions:

• The developed colloidal suspension serves as a versatile model system for studying crystal melting and phase transitions.
• This model advances the understanding of phenomena relevant to electro- and magneto-rheological fluids.
• Enables quantitative real-space investigations previously not possible.