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Herein, we investigate supramolecular gelation behavior of a dendronized triphenylamine bis-urea macrocycle (1) in toluene in the presence and absence of sulfoxide chain stoppers. Macrocycle 1 assembles in the sol phase through intermolecular hy-drogen bonding interactions, spontaneously transitioning into a gel state when left undisturbed at room temperature. In tolu-ene, 1 displays a critical gelation concentration of 0.066 wt%, classifying it as a super-gelator. Furthermore, it exhibits a thermoreversible gel-sol phase transition as well as thixotropic behavior. Temperature-dependent 1H NMR spectroscopy is employed to probe the sol phase assembly of 1 with the size variations at different temperatures assessed by 2D DOSY. Rheological experiments at 10 °C were used to measure gelation response to mechanical stimuli. An amplitude sweep test highlights a linear viscoelastic region. Additionally, the self-healing behavior of gel 1 was verified through a series of strain cycles, where it showed complete recovery. Addition of chain stoppers 10% versus 1 of dimethyl sulfoxide (DMSO) and diphenyl sulfoxide (DPS) lead to weaker gels with smaller differences between the storage and the loss moduli. Rheological analysis revealed slower/partial recovery for the gel containing chain stoppers. Gels assembled from macrocyclic building blocks may retain homogeneous binding cavity and channels offering novel functional properties.
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Less is more when forming gels by dilution
Soft materials that change form or function in response to environmental or user-applied stimuli have a wide range of biomedical applications ( 1 ). Gels can form in water from weakly interacting molecules but can return to the state of a flowing liquid suspension, known as a sol, upon changes in the concentration of the molecules or the applied temperature. This behavior is known as a reentrant phase transition. A gel-to-sol phase transition typically arises from a reduction in concentration, meaning that a gel becomes a sol upon dilution and a sol becomes a gel with increased concentration. On page 213 of this issue, Su et al. ( 2 ) demonstrate a system that exhibits a sol-to-gel transition when diluted, inverting the common behavior of gels. Their observations offer insight into systems that undergo reentrant phase transitions in biology.
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- Award ID(s):
- 1944875
- PAR ID:
- 10398892
- Date Published:
- Journal Name:
- Science
- Volume:
- 377
- Issue:
- 6602
- ISSN:
- 0036-8075
- Page Range / eLocation ID:
- 153 to 154
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1126/science.abo7656
