Stimuli-Responsive Colloidal Assembly Driven by Surface-Grafted Supramolecular Moieties

A robust method is described for precisely functionalizing silica colloids with short-chain alkanes and self-associating o-nitrobenzyl protected benzene-1,3,5-tricarboxamides (BTAs). Controlled deprotection affords activation of the latent supramolecular moieties by facilitating short-range hydrogen-bonding interactions between surface-functionalized silica particles. Control of mesoscale assembly of the responsive colloidal suspensions is demonstrated with two different external triggers. First, the amount of active (i.e., deprotected) BTAs is efficiently tuned by varying the exposure time to UV radiation. Controlled activation of the BTAs translates to regulating the valence of the system. After activation, the binding strength of individual BTAs can be modulated with temperature, providing an additional handle with which the assembly behavior is manipulated. This dual-regulation approach is a powerful and sensitive avenue for controlling colloidal assembly processes.