Electrokinetics at high ionic strength and hypothesis of the double layer with zero surface charge

Area of Science:

• Colloid and Surface Science
• Physical Chemistry
• Electrochemistry

Background:

• Interfacial water structure influences electrical double layers (DL) via ion solvation.
• The
• zero surface charge
• DL model proposes DL formation due to ion concentration differences, not surface charge.
• Previous theoretical models by Dukhin, Derjaguin, Yaroschuk, and Mancui & Ruckenstein.

Purpose of the Study:

• To experimentally verify the
• zero surface charge
• DL model.
• To investigate the effect of nonionic surfactants on interfacial layers at high ionic strength.
• To develop new methods for characterizing interfacial layers.

Main Methods:

• Electroacoustic technique for high ionic strength measurements (up to 2 M).
• Zeta potential measurements.
• Acoustic attenuation measurements for surfactant adsorption characterization.

Main Results:

• Confirmed a significant zeta potential (8 ± 1 mV) for alumina in 1 M KCl, supporting the
• zero surface charge
• DL model.
• Observed that high KCl concentrations (>0.1 mol/dm3) inhibit nonionic surfactant (Tween 80) adsorption.
• Developed acoustic attenuation method to characterize surfactant adsorption.

Conclusions:

• Experimental evidence supports the existence of a double layer without surface charge.
• High electrolyte concentrations significantly alter interfacial layer properties by preventing surfactant adsorption.
• New acoustic methods offer potential for detailed interfacial structure analysis at high ionic strength.