Role of Acids in Stabilizing Reverse Micelles: Insights from Dodecyl Sulfate

Area of Science:

• Physical Chemistry
• Materials Science
• Computational Chemistry

Background:

• Anionic surfactant sodium dodecyl sulfate (SDS) forms reverse micelles (RMs) in non-miscible solvents above the critical micelle concentration (CMC).
• Previous studies explored RMs in salt or alkali solutions, but the mechanism of acids in SDS RMs remains less understood.

Purpose of the Study:

• To elucidate how four different acids (fluoroboric, chloroauric, phosphoric, and sulfuric) affect the interfacial organization, electrostatics, and morphology of SDS RMs in toluene.
• To provide molecular insights into acid-induced modifications of SDS RMs.

Main Methods:

• All-atom molecular dynamics simulations utilizing the Generalized Amber Force Field.
• Investigation of SDS-based RMs in toluene with four distinct acids: HBF4, HAuCl4, H3PO4, and H2SO4.

Main Results:

• Acid addition reduces SDS headgroup mobility and tail ordering by forming persistent hydrogen-bond networks, altering interfacial dynamics and flexibility.
• Acids influence interfacial tension (γ) in the order: γ(HBF4) > γ(H2SO4) > γ(HAuCl4) > γ(H3PO4).
• Reduced micellar wall flexibility and interfacial tension promote the formation of larger, more stable RMs.

Conclusions:

• Acids significantly modulate the structure and stability of SDS RMs through specific interfacial interactions.
• These findings offer molecular-level guidance for controlling RM properties in nanoparticle synthesis, influencing nucleation, growth, and structural outcomes.