Micelle conformation of sodium alkyl sulfate surfactants with different hydrophobic chain length: A molecular dynamics study

Based on all-atom molecular dynamics (MD) simulation, micelle properties and microstructures of sodium alkyl sulfate (SAS) with different hydrophobic chain length in explicit aqueous solution are investigated. With the growth of hydrophobic alkyl chain (C8 - C16), the shape of micelle gradually transform from spherical micelle into ellipsoidal or cylindrical aggregate. Longer hydrophobic tail chains collapse inside the micelle and results the smaller exposed surface, which leads to the decreased solvent accessible surface area (SASA) and hydrogen bond. The conformation of C8 - C14 micelles is solid sphere or ellipsoid and the effect of expanding space by the hydrophobic tail chains is dominant. And the hydrophobic tail chains of C16 micelle collapse inside the micelle and extend to the micelle shell but do not expose to the surface of the micelle. The motion of shorter alkyl chain in micelle is restrictive and longer alkyl chain is active. Longer hydrophobic alkyl chain prompts the SAS molecules to move form aqueous solution to form micelle spontaneously due to the increase of entropy.