Simple Estimate of the Potential Drop across an Amphiprotic Liquid-Liquid Interface

Area of Science:

• Electrochemistry
• Physical Chemistry
• Interface Science

Background:

• Immiscible liquids exhibit different internal electrostatic potentials, forming electric double layers (EDLs).
• Proton exchange in amphiprotic liquids creates distinct positively and negatively charged EDLs at the interface.
• Understanding liquid-liquid junction potentials is vital for electrochemical applications.

Purpose of the Study:

• To develop a method for estimating the potential drop (Galvani potential) between two immiscible liquids.
• To determine the electric field strength across the liquid-liquid interface.
• To provide a model independent of surface charge and ionic strength.

Main Methods:

• Utilizing pKa and pKb values of one liquid dissolved in another.
• Calculating pH equivalents within each amphiprotic liquid.
• Employing ionic strength to determine EDL thickness.

Main Results:

• A formula was derived to estimate the potential drop (Δφ) using acid-base properties and pH.
• The estimation method is independent of surface charge and ionic strength.
• The average electric field strength across the interface was estimated based on EDL thickness.

Conclusions:

• The study presents a novel method to quantify Galvani potential and electric field strength at liquid-liquid interfaces.
• This approach offers a way to predict interfacial potentials based on chemical properties.
• The findings are applicable to systems like water-alcohol interfaces, with a specific formula provided.