Directing colloidal self-assembly using supramolecular chemistry
Eindhoven University of Technology in the Netherlands
Controlling colloidal interactions is highly important in view of the large number of applications of colloid based materials. We recently demonstrated the use of supramolecular moieties as a versatile tool to modulate surface forces . To this end we decorate silica colloids with supramolecular motifs, whose interactions are strong, directional and temperature-reversible in solution . While literature on supramolecular polymers is extensive, little is known about their impact on colloidal phase behaviour . We use as supramolecular moiety benzene-1,3,5-tricarboxamide (BTA) derivatives which recognize and selectively interact with identical BTA derivatives through 3-fold intermolecular hydrogen bonding. The BTA is also equipped with a photo-cleavable group, which blocks the formation of the hydrogenbonds when present. This molecular design allows for tuning of colloidal self-assembly by two
independent external triggers: UV-light and temperature. The synthesized supramolecular colloids were characterized by several techniques and their self-assembly upon UV irradiation was followed by means of confocal microscopy. These studies reveal that the particles remain as singlets prior to photoactivation. Illumination by UV-light photo-cleaves the protecting group initiating hereby the short-range hydrogen-bonding interactions between tethered supramolecular moieties, which in turn triggers colloidal clustering. Hence, mesoscale colloidal assembly is a direct consequence of externally triggered intermolecular hydrogen bonding at the molecular level demonstrating that small surface-grafted molecules can have a dramatic effect on the behaviour of micron-sized colloidal particles. The modularity of the light-induced colloidal assembly has also been explored; i.e., the impact of temperature and the amount of active sites on the interaction strength as well as the nature of the active tethered moieties on colloidal self-sorting through orthogonal specific interactions. Finally, we explore the use of these dual responsive colloids to generate ‘smart’ Pickering emulsions.
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