Influence of the Porphyrin Structures on the Contact Angle of Water Wetting by Langmuir-Schaefer Films

Studying the contact angle of water droplets on the surfaces of thin films formed by organic compounds allows to establish hydrophilic/hydrophobic properties of the films. Knowledge of hydrophilicity/hydrophobicity makes it possible to optimize the composition and increase the adhesive properties of films, improving their functionality. In this study, the dependence of the contact angle of Langmuir-Schaefer films (LS-films) of three compounds: 5,10,15,20-tetraphenylporphyrin (I), 2-aza-21-carba-5,10,15,20-tetraphenyl-porphyrin (II), and 5,15-bis(2,6-bis(dodecycloxy)phenyl)porphyrin (III) was examined. Contact angle data were obtained for LS-films with different transfer numbers of floating layers of the studied porphyrins and different surface roughness. It was found that LS-films of compounds I and II are hydrophobic and their hydrophobicity increases with an increasing of transfer number. In addition, an increase in the surface roughness of the LS film of compound I compared to compound II reduces the value of the contact angle. Unlike porphyrins I and II, LS-films of compound III displayed hydrophilic properties. The obtained data can be used for the targeted design of compounds to create thin film materials of various purposes.