Microelectrophoresis of Silica Rods Using Confocal Microscopy

Area of Science:

• Colloid and Surface Science
• Physical Chemistry
• Nanotechnology

Background:

• Electrophoretic mobility and zeta potential (ζ) are crucial for understanding colloidal particle behavior.
• Previous studies often assumed isotropic particle movement in electric fields.
• Rod-like particles, like colloidal silica, can exhibit complex motion dependent on orientation.

Purpose of the Study:

• To determine the electrophoretic mobility and zeta potential (ζ) of fluorescently labeled colloidal silica rods.
• To investigate the orientation-dependent velocity of silica rods during electrophoresis.
• To analyze the influence of double layer thickness (κa) on anisotropic electrophoretic mobility.

Main Methods:

• Microelectrophoresis measurements using confocal microscopy.
• Recording xyz-stacks of particle movement in an electric field.
• Varying solvent polarity and electrolyte concentration to tune double layer thickness (κa).

Main Results:

• Measured orientation-dependent velocity of individual silica rods as a function of κa.
• Determined anisotropic electrophoretic mobility for silica rods with varying double layer sizes.
• Observed orientation-dependent velocity even at high κa (κa > 10).
• Found increasing anisotropy with decreasing κa, except in low polar solvents (κa < 1) where anisotropy decreased due to end effects.

Conclusions:

• Electrophoretic mobility of colloidal silica rods is anisotropic and depends on orientation relative to the electric field.
• End effects become significant in low polar solvents, reducing mobility anisotropy.
• Accurate zeta potential (ζ) determination requires accounting for orientation-dependent mobility and end effects, especially at low κa.