The principles of molecular gel formation
Molecular gels are associated with the formation of strongly anisotropic structures at low volume fractions (less than 1 wt%) that induce solid-like mechanical properties. Low molecular weight gelators based on aromatic short peptide derivatives have been shown to self-assemble into fibrous networks featuring highly ordered molecular packing. The building units of these structures are individual molecules experiencing hydrogen bonding and π-π stacking interactions, making them distinct from typical gels formed by aggregation of colloidal particles or crosslinking of polymer chains. The remarkable structural and mechanical properties of these materials offer a wide range of potential applications. Despite a surge in scientific publications on a variety of molecular gelators over the past decade, the mechanism and fundamental thermodynamic principles of molecular gel formation remain poorly understood. The aim of this thesis is to address these issues by a thorough and systematic experimental characterization of a model molecular gelator, fluorenylmethoxycarbonyl diphenylalanine (Fmoc-FF). The nature of the gel transition, as well as the relationship between composition, dynamics, structural and mechanical properties are discussed within the framework of current soft matter theories. The experimental observations reveal that the formation of the gel is a result of the system undergoing an equilibrium first order phase transition and a generalized phase diagram is developed.
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign