Low-molecular-weight gels show great potential for application in fields ranging from the petrochemical industry to healthcare and tissue engineering. These supramolecular gels are often metastable materials, which implies that their properties are, at least partially, kinetically controlled. Here we show how the mechanical properties and structure of these materials can be controlled directly by catalytic action. We show how in situ catalysis of the formation of gelator molecules can be used to accelerate the formation of supramolecular hydrogels, which drastically enhances their resulting mechanical properties. Using acid or nucleophilic aniline catalysis, it is possible to make supramolecular hydrogels with tunable gel-strength in a matter of minutes, under ambient conditions, starting from simple soluble building blocks. By changing the rate of formation of the gelator molecules using a catalyst, the overall rate of gelation and the resulting gel morphology are affected, which provides access to metastable gel states with improved mechanical strength and appearance despite an identical gelator composition.
A prototype surfactant system was developed with the unique feature that it can be switched between an aggregated, amphiphilic state and a nonaggregated, nonamphiphilic state using external stimuli. This switchable surfactant system uses the reversible formation of a dynamic covalent bond for pH- and temperature-triggered on/off self-assembly of micellar aggregates by reversible displacement of the equilibrium between nonamphiphilic building blocks and their amphiphilic counterparts. The potential for application in controlled-release systems is shown by reversible uptake and release of an organic dye in aqueous media.
Breaking bilayers: Incorporation of dynamic covalent bonds in vesicle‐forming surfactants leads to the formation of responsive vesicles, which can be switched back and forth between the bilayer state and the isotropic solution using either dilution or a change in the pH value as external stimuli.
Come together: Self‐assembly can drive the formation of conjugated imine polymers in water, and stabilization of otherwise unstable imine bonds is used to obtain fully π‐conjugated, responsive dynamic covalent polyimines in aqueous environments. Both the optical properties and the aggregate morphology can be tuned by varying the aromatic monomers.
Dynamic covalent chemistry is a powerful tool for the construction of adaptive and stimulus-responsive nanosystems. Here we report on the spontaneous formation of dynamic covalent wormlike micelles from imine-based gemini surfactants, formed upon mixing aqueous solutions of two complementary non-surface-active precursors. Resulting from the reversibility of the dynamic covalent imine bond, the wormlike micelles can be switched between an isotropic solution and the assembled state, triggered by pH and temperature. Thermodynamic modeling of the reaction equilibria shows that, although mixtures of single- and double-tailed surfactants are formed, it is mainly the double-tailed surfactant that assembles into the wormlike micelles.
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