Charging Poly(methyl Methacrylate) Latexes in Nonpolar Solvents: Effect of Particle Concentration

Area of Science:

• Colloid Science
• Physical Chemistry
• Materials Science

Background:

• Electrophoresis studies charged colloids in nonpolar solvents.
• Poly(methyl methacrylate) (PMMA) latexes stabilized by poly(12-hydroxystearic acid) in dodecane were used.
• Aerosol OT (AOT) surfactant acted as the charging agent.

Purpose of the Study:

• Investigate the decrease in electrophoretic mobility (μ) of PMMA latexes with increasing particle volume fraction.
• Determine the cause of decreased mobility: surfactant reservoir depletion or interparticle interactions.
• Accurately determine the electrokinetic zeta (ζ) potential.

Main Methods:

• Electrophoresis measurements were conducted at varying particle concentrations.
• Contrast-variation small-angle neutron scattering (SANS) with deuterated AOT (AOT-d34) studied surfactant incorporation.
• Electrokinetic modeling was employed to analyze interparticle interactions.

Main Results:

• Electrophoretic mobility (μ) decreased as particle concentration increased.
• SANS confirmed consistent AOT-d34 incorporation across all volume fractions, ruling out surfactant depletion.
• Solvodynamic and electrical interactions between particles were identified as the cause of mobility decrease.

Conclusions:

• Interparticle interactions, not surfactant depletion, explain the reduced electrophoretic mobility in PMMA latexes.
• These interactions are present at all accessible particle volume fractions.
• Accounting for these interactions is essential for accurate electrokinetic zeta (ζ) potential determination in charged colloidal systems.