Overlapping double layers in electrokinetics of concentrated dispersions

Area of Science:

• Colloid and Surface Science
• Physical Chemistry
• Electrochemistry

Background:

• The traditional Isolated Double Layer (DL) model fails in concentrated dispersions due to DL overlap.
• Previous theories predicted decreased electrophoretic mobility with DL overlap.
• Recent
• quasi-homogeneous DL theory
• suggests increased mobility at complete DL overlap.

Purpose of the Study:

• To experimentally verify theoretical predictions regarding electrophoretic mobility in concentrated dispersions with overlapping DLs.
• To investigate the behavior of electrophoretic mobility and zeta potential as a function of particle volume fraction.

Main Methods:

• An equilibrium dilution protocol was used to maintain electrochemical equilibrium across varying volume fractions (1-36% vl).
• Electroacoustic techniques were employed to measure electrophoretic mobility and zeta potential.
• Measurements were conducted across a wide range of volume fractions to observe DL overlap effects.

Main Results:

• Electrophoretic mobility and zeta potential remained constant up to 15% volume fraction.
• Above 15% volume fraction, where DLs overlap, both electrophoretic mobility and zeta potential increased.
• The experimental results qualitatively support the
• quasi-homogeneous DL theory
• .

Conclusions:

• The
• quasi-homogeneous DL theory
• accurately predicts the increase in electrophoretic mobility in concentrated dispersions with overlapping DLs.
• The findings challenge older theories that predicted a decline in mobility due to DL overlap.
• This research provides experimental validation for electrokinetic phenomena in concentrated colloidal systems.