Structural evolution in self-assembled gels

The use of self-assembled gel in biomaterials and drug delivery is an important new area of research, with these novel materials possessing both physical and chemical advantages over current bio-polymers. However, as gel research expands, key elements of the self-assembly process and gel network formation are still poorly understood. If these gels are to be introduced into biological systems, a better model for gelation is needed which incorporates the structural behaviour and molecular interactions, which help define the stability of gels during the initial gelation process and over the long term.A novel family of gelator molecules, tetraalkyl pyromellitamides, were previously thought to be a model gel system and form in a hierarchical process as proposed in literature for other self-assembled gel systems. A range of gels were synthesised and tested to determine the effects of small changes to the molecule on the larger bulk gel. Through AFM and TEM imaging, it was found that the gel system does not follow a linear growth mechanism; instead it is a dynamic material which changes unexpectedly over a week. A large initial structure separates into smaller fibres which ten entangle to form super-structures on the nano-scale. Rheological profiles of the gels showed changes in viscosity and stiffness of the gels as they were aged, along with the differences in the initial gel formation.To examine what is causing these changes in the structure, X-Ray and neutron scattering were used to characterise the individual fibres which make up the larger fibres observed in the microscopy images. This data confirmed that a one-dimensional stacking mechanism was responsible for the fibre formation, and these fibres were effectively stretching out over time. To investigate the inter- and intra-molecular interactions, along with the role of the solvent molecules, a new synthesis was devised to produce per-deuterated gelators. Using solid-state deuterium-NMR, the mobility and orientation of the side-chains was observed, showing that the gelator is dynamic even when immobilized at low temperature