Temporal Evolution of Interparticle Potentials of PMMA Colloids in CHB/Decalin

Area of Science:

• Colloid and Interface Science
• Soft Matter Physics
• Optical Microscopy

Background:

• Polymethylmethacrylate (PMMA) particles in cyclohexyl bromide/decalin are model systems for optical microscopy.
• Simultaneous density and refractive index matching is achievable, but hard potential particle preparation is difficult.
• Significant sample parameter variations are common despite identical preparation.

Purpose of the Study:

• Investigate the cause of variations in PMMA colloidal dispersion properties.
• Quantify the temporal evolution of particle charging.
• Assess the effect of tetrabutylammonium bromide (TBAB) salt on interparticle forces.

Main Methods:

• Blinking optical tweezers method for force measurements.
• Analysis of highly diluted PMMA dispersions over extended periods (tens of days).
• Controlled addition of TBAB salt to study electrostatic force modulation.

Main Results:

• Temporal evolution of particle charging identified as the cause of property variations.
• Small concentrations of TBAB salt significantly reduce electrostatic forces between PMMA particles.
• Non-negligible contact potentials remain even at high TBAB concentrations.

Conclusions:

• Particle charging dynamics are critical for the stability and predictability of PMMA colloidal systems.
• TBAB salt effectively screens electrostatic interactions, offering a method to control interparticle forces.
• Understanding residual contact potentials is essential for precise colloidal system design.