Understanding the role of H-bonding in self-aggregation in organic liquids by fatty acid amphiphiles with a hydrocarbon tail containing different H-bonding linker groups

Abstract

In this work, we have designed and synthesized a series of fatty acid amphiphiles that have the same structural skeleton but different hydrogen-bonding (H-bonding) functional groups in the hydrocarbon chain. To examine the importance of the H-bonding interaction on the formation of a one-dimensional (1D) aggregate in organic solvents, we have compared the gelation behavior of these amphiphiles in some common organic solvents at room temperature. Despite the structural similarity, the amphiphiles were observed to exhibit different gelation behavior. The organogels were characterized using conventional techniques such as field emission scanning electron microscopy, X-ray diffraction, and rheology. A systematic analysis of the FT-IR and (1)H NMR spectral data, gel melting temperatures, and mechanical strengths of the organogels in a given solvent suggested the importance of H-bonding as well as van der Waals interaction in the gelation process. In this study, we have made an attempt to estimate qualitatively the relative contribution of H-bonding and van der Waals interactions between gelator molecules forming organogels. The results suggest that strong and weaker H-bonding affects the gelation ability of gelators. However, when the H-bonding interaction is weak, an increase in van der Waals interactions can result in gelation, but when both H-bonding and van der Waals interactions are weak, that is, when the amphiphiles are liquid and semisolid, no gelation is observed. It is concluded that a balance between H-bonding and van der Waals interactions is necessary for physical gelation.