Investigating multigelator systems across multiple length scales.

Preparation of multicomponent systems provides a method for changing the properties of low molecular weight gelator (LMWG)-based systems. Here we have prepared a variety of multicomponent systems where both components are N-functionalised dipeptide-based LMWGs that may either co-assemble or self-sort when mixed. We exemplify how varying the concentration ratio of the two components can be used to tune the properties of the multicomponent systems pre-gelation, during gelation and in the gel state using viscosity and rheology measurements, circular dichroism, NMR and small angle neutron scattering. We also investigate the effect of changing the chirality of a single component on the properties of these systems. While predicting the outcome of multicomponent assembly is a challenge, the preparation of a variety of systems allows us to probe the factors affecting their design. This work provides insights into how the properties of multicomponent systems composed of two gelators with the same basic structural design can be tuned by varying the chirality and the concentration ratio of the two components and considering the behaviour of the two components when alone.

Hierarchical Composite Self-Sorted Supramolecular Gel Noodles.

Multicomponent supramolecular systems can be used to achieve different properties and new behaviors compared to their corresponding single component systems. Here, a two-component system is used, showing that a non-gelling component modifies the assembly of the gelling component, allowing access to co-assembled structures that cannot be formed from the gelling component alone. The systems are characterized across multiple length scales, from the molecular level by NMR and CD spectroscopy to the microstructure level by SANS and finally to the material level using nanoindentation and rheology. By exploiting the enhanced mechanical properties achieved through addition of the second component, multicomponent noodles are formed with superior mechanical properties to those formed by the single-component system. Furthermore, the non-gelling component can be triggered to crystallize within the multicomponent noodles, allowing the preparation of new types of hierarchical composite noodles.

Enhancement of the mechanical properties of lysine-containing peptide-based supramolecular hydrogels by chemical cross-linking.

Exposure of lysine-containing peptide-based gelators to the cross-linking agent glutaraldehyde allows tuning of gel mechanical properties. The effect of cross-linking depends on the position of the lysine residue in the peptide chain, the concentration of gelator and the conditions under which cross-linking takes place. Through control of these factors, cross-linking leads to increased gel strength.

Exploiting and controlling gel-to-crystal transitions in multicomponent supramolecular gels.

Multicomponent supramolecular gels provide opportunities to form materials that are not accessible when using the single components alone. Different scenarios are possible when mixing multiple components, from complete co-assembly (mixing of the components within the self-assembled structures formed) to complete self-sorting such that each structure contains only one of the components. Most examples of multicomponent gels that currently exist form stable gels. Here, we show that this can be used to control the mechanical properties of the gels, but what is probably most exciting is that we show that we can use a magnetic field to control the shape of the crystals. The gelling component aligns in a magnetic field and so results in anisotropic crystals being formed.

Understanding gel-to-crystal transitions in supramolecular gels.

Most supramolecular gels are stable or assumed to be stable over time, and aging effects are often not studied. However, some gels do show clear changes on aging, and a small number of systems exhibit gel-to-crystal transitions. In these cases, crystals form over time, typically at the expense of the network underpinning the gel; this leads to the gel falling apart. These systems are rare, and little is known about how these gel-to-crystal transitions occur. Here, we use a range of techniques to understand in detail a gel-to-crystal transition for a specific functionalised dipeptide based gelator. We show that the gel-to-crystal transition depends on the final pH of the medium which we control by varying the amount of glucon-δ-lactone (GdL) added. In the gel phase, at low concentrations of GdL, and at early time points with high concentrations of GdL, we are able to show the nanometre scale dimensions of the self-assembled fibre using SAXS; however there is no evidence of molecular ordering of the gel fibres in the WAXS. At low concentrations of GdL, these self-assembled fibres stiffen with time but do not crystallise over the timescale of the SAXS experiment. At high concentrations of GdL, the fibres are already stiffened, and then, as the pH drops further, give way to the presence of crystals which appear to grow preferentially along the direction of the fibre axis. We definitively show therefore that the gel and crystal phase are not the same. Our work shows that many assumptions in the literature are incorrect. Finally, we also show that the sample holder geometry is an important parameter for these experiments, with the rate of crystallisation depending on the holder in which the experiment is carried out.