Particle Size-Dependent Electrophoresis in Polymer Solutions

Area of Science:

• Colloid and Surface Science
• Rheology
• Electrophoresis

Background:

• The Smoluchowski velocity, describing electrophoretic particle motion, is traditionally considered size-independent in Newtonian fluids under thin-Debye-layer conditions.
• Recent theories suggest that fluid rheology can induce particle size dependence in electrophoresis, particularly in non-Newtonian fluids.

Purpose of the Study:

• To experimentally demonstrate the predicted rheology-induced particle size dependence of electrophoresis.
• To investigate this phenomenon in viscoelastic poly(ethylene oxide) (PEO) solutions.

Main Methods:

• Comparison of electrophoretic velocities of three different-sized particles in a Newtonian buffer.
• Measurement of electrophoretic velocities of the same particles in viscoelastic PEO solutions.
• Systematic variation of PEO concentration and polymer length to study their effect on particle size dependence.

Main Results:

• Particles exhibited identical electrophoretic velocities in the Newtonian buffer, consistent with the Smoluchowski model.
• In PEO solutions, a clear trend of increasing electrophoretic velocity with increasing particle size was observed.
• This particle size dependence intensified with higher PEO concentrations and longer polymer chains, correlating with increased fluid elasticity.

Conclusions:

• This study provides the first experimental evidence of particle size-dependent electrophoresis in viscoelastic non-Newtonian fluids.
• The findings validate theoretical predictions regarding the influence of fluid elasticity on electrophoretic behavior.
• Enhanced fluid elasticity, quantified by the elasticity number, is identified as the key factor driving the observed particle size dependence.