New Methods to Calculate the Micelle Aggregation Equilibrium Constant and the Mole Gibbs Free Energy in a Larger Region of Surfactant Concentration

Abstract

The methods are brought forward to calculate the dimerization equilibrium constant and the mole Gibbs free energy of surfactant in low surfactant concentration according to the forming theories of the organized assembly of surfactant molecule and chemical equilibrium. And a new simple and suitable method is educed to calculate the micelle aggregation equilibrium constant and the mole Gibbs free energy in large‐scale surfactant concentration. In SDS/H₂O system, the dimerization equilibrium constant K_d=7.6±0.1×10³, the mole Gibbs free energy ΔG_m,d=−11.07±0.03 kJ · mol⁻¹. In SDS/H₂O system and SDS/BA/H₂O microemulsion system, the mole Gibbs free energy of spherical micelle ΔG_m,s≈−10.88 kJ · mol⁻¹, the mole Gibbs free energy of rod‐like micelle ΔG_m,r≈−9.80 kJ · mol⁻¹.

Keywords:

• Mole Gibbs free energy
• aggregation equilibrium constant
• surfactant
• micelle

This work was supported by the National Natural Science Foundation of China (20573091, 20233010).