Solvent-gelator interactions-using empirical solvent parameters to better understand the self-assembly of gel-phase materials

By studying a family of L-lysine bis-urea gelators with variable peripheral groups in different solvents, a more detailed understanding of the way in which gelator fibres interact with the surrounding solvent environment is obtained. In all cases, these gelators establish the same hydrogen bonding molecular recognition pathways-however, this process is mediated by the nature of the solvent. In terms of Kamlet-Taft parameters, the a parameter of the solvent (hydrogen bond donor ability) has primary importance in controlling whether the gelator can establish a hydrogen bond network; the beta parameter (hydrogen bond acceptor ability) plays a secondary role in tuning the thermal stability of the gel, and the pi* parameter (polarisability) controls the solvation of the peripheral groups on the gelator by the solvent, and hence tunes the gel stability and the ability of the gelator to establish fibre-fibre interactions, as evidenced by scanning electron microscopy imaging. Considering solvent parameters allows us to gain a unique insight into hierarchical assembly processes at different length scales, i.e., molecular scale gelator-gelator interactions, and nanoscale fibre-fibre and fibre-solvent interactions. These processes are at the heart of developing effective models for the dynamic assembly of gel-phase soft materials.