Molecular dynamics simulations on tetraalkylammonium interactions with dodecyl sulfate micelles at the air/water interface

Abstract

Different Tetraalkylammonium (TAA+) counterions including tetramethylammonium (TMA+), tetraethylammonium (TEA+), tetrapropylammonium (TPA+) and tetrabutylammonium (TBA+) with dodecyl sulfate (DS−) at the air/water interface were studied with atom molecular dynamics (MD) simulations. Structural properties such as the distribution of polar head at the interface, probability of gauche defects, order parameters, length and angle distributions were investigated. The counterions and DS− form mixed adsorption layer. Our results show that weak CHO hydrogen bonds are formed between the polar head and alkane chains of counterions. The weak hydrogen bonds play an important role in the formation of mixed adsorption layer. Mainly four interaction patterns exit between TAA+ and DS− ions, in which binding pattern II, representing that two terminal methyl groups of TAA+ penetrate into the monolayer, is the most favorable one.