| The supramolecular hydrogels showing responses to external stimuli may be applied to drug delivery,optical devices,actuators and self-healing materials.Host-guest interaction is an important driving force on account of their high selectivity,tunable binding constants and special steric effects.Cyclodextrins(CDs)are most commonly chosen because of their easy acquirement,good solubility,good modifiability,and low toxicity.However,the construction of stimuli-responsive mono-component host-guest hydrogels remains a challenge in that it is still hard to balance the solubility and gel ability for the gelator.In this work,three azobenzene modified ?-cyclodextrins derivatives with different alkyl length(?-CD-Azo-Cn)have been synthesized.The length of alkyl dramatically influences the solubility and gel ability of ?-CD derivatives in water.Among these derivatives,?-CD-Azo-C8 possesses the lowest minimum gelation concentration(MGC).The NMR spectra of gelators at different concentrations indicate that the azobenzene group enters into the CD from the primary(wide)rim.Based on host-guest interaction between ?-CD and azobenzene units in aqueous solution,which is confirmed by UV-visible and ROESY NMR spectra,the gelators self-assemble and further interwine into networks through the hydrogen bonds on the surface of ?-CD cavities.The hydrogel formed by mono-component gelator can collapse under the external stimuli such as heating,competition guest and host,and UV irradiation.When the concentration of gelator is more than 8 wt%,the hydrogel exhibits good self-supporting ability with a storage modulus higher than 104 Pa.The saturated storage modulus reaches 5.7×105 Pa,which means the hydrogel has the property of anti-deformation. |
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