Photosensitive Cationic Azobenzene Surfactants: Thermodynamics of Hydration and the Complex Formation with Poly(methacrylic acid)

Abstract

In this computational work we investigate the photosensitive cationic surfactants with the trimethylammonium or polyamine hydrophilic head and the azobenzene-containing hydrophobic tail. The azobenzene-based molecules are known to undergo a reversible trans-cis-trans isomerization reaction when subjected to UV-Visible light irradiation. Combining the density functional theory and the all-atom molecular dynamics simulations, the structural, optical and the hydration properties of the trans- and the cis-isomers and their interaction with the oppositely charged poly(methacrylic acid) in aqueous solution are investigated. We establish and quantify the correlations of the molecular structure and the isomerization state of the surfactants and their hydrophilicity/hydrophobicity and the self-assembling altered by light. For this reason, we compare the hydration free energies of the trans- and the cis-isomers. Moreover, the investigations of the interaction strength between the azobenzene molecules and the polyanion provide additional elucidations of the recent experimental and theoretical studies on the light triggered reversible deformation behaviour of the microgels and the polymer brushes loaded with azobenzene surfactants.