Effect of Bond Rigidity and Molecular Structure On the Self Assembly of Amphiphilic Molecules Using Second Order Classical Density Functional Theory

Amphiphilic molecules such as surfactants contain both hydrophilic and hydrophobic portions. This duel molecular identity drives surfactant self assembly at fluid / fluid interfaces which in turn affects the thermodynamic and interfacial properties of the system (e.g., reduced interfacial tension). Surfactant self assembly at the air / water interface has been subjected to extensive study and analysis; however, liquid / liquid interfaces such as water / oil have received less attention. With extensive use of surfactants in several industrial applications and consumer goods such as shampoos, detergents, and enhanced oil recovery, the need for targeted molecular design to maximize the efficiency and effectiveness of surfactant performance in these processes will become increasingly important.

We have developed a second order density functional theory which provides an accurate and efficient method to study the effect of molecular structure on surfactant self assembly at the oil / water interface. Some of the features investigated here are the effect of the relative locations of the hydrophobic and hydrophilic portions of the molecule, rigidity (including bond angle) versus flexibility on the structure of the interface, and how these variables are related to reduction of interfacial tension.