Solubilization of octane in cationic surfactant-anionic polymer complexes: Effect of ionic strength

Area of Science:

• Colloid and Surface Science
• Physical Chemistry
• Polymer Science

Background:

• Surfactant-polymer interactions influence the solubilization of hydrophobic molecules.
• Ionic strength is a critical factor modulating these interactions and solubilization behavior.

Purpose of the Study:

• To investigate the effect of ionic strength on the thermodynamics of octane solubilization.
• To understand the role of carboxymethyl cellulose (anionic polymer) and cetyltrimethylammonium bromide (cationic surfactant) interactions.

Main Methods:

• Isothermal titration calorimetry (ITC) was employed to study octane oil-in-water emulsions.
• System composition involved carboxymethyl cellulose, cetyltrimethylammonium bromide (CTAB), and varying NaCl concentrations.

Main Results:

• Carboxymethyl cellulose binding capacity for CTAB increased with NaCl concentration up to 100 mM.
• Octane solubilization thermodynamics in CTAB micelles strongly depended on ionic strength.
• Increased ionic strength made solubilization less endothermic or exothermic, boosting capacity and favoring enthalpy-driven processes.

Conclusions:

• Solubilization is primarily driven by enthalpy, particularly at higher ionic strengths.
• Increasing ionic strength leads to greater Gibbs energy decrease and smaller unfavorable entropy changes for octane solubilization.
• Ionic strength is a key parameter controlling hydrophobic molecule solubilization in polymer-surfactant systems.