Supramolecular Assemblies Based On Multiple Hydrogen Bonds For Photo-responsive Actuators

Supramolecular assembly based on multiple hydrogen bonds is a simple way for the preparation of photo-responsive actuators.As a chromophore,azobenzenes have been introduced in polymers to get supramolecular assembly.Multiple H-bonds not only facilitate the conversion of microscopic motion into macroscopic deformation,but also have the potential for stabilizing the Z-isomers.Moreover,the rate and degree of deformation could be controlled by H-bonds.Therefore,multiple H-bonds crosslinking azobenzene/polymer is an ideal material for the preparation of photo-responsive actuators.The absorption properties of azobenzenes depend on the kinds,positions and numbers of the substituent groups.The ?-?* absorption for pull-push azobenzenes were found in the visible light range,and the cis-isomers are unstable.Moreover,the formation of inter-/intra-molecular hydrogen bond between carboxy groups and solvent molecules or N=N can also improve the stability of cis-isomers.In this paper,polyacrylic acid(PAA)grafted with 2-ureido-4[1H]-pyrimidinone(UPy)and tertracarboxylated azobenzene(t-Azo)were parepaed fistly.Then supramolecular assembly of PAA-u/t-Azo was prepared by multiple H-bonds.Free standing PAA-u/t-Azo film was prepared by dip-coasting under UV irradiation.The content of cis-isomers is 25%.The film performed excellent light-induced deformation and a good cycling staility for 100 cycles then the half-life of film was 120 h.The angles of deformation were controlled by illumination(90o—170o)and the film could return to original shape under UV irradiation and could keep in this shape for 240 h.Based on this deformation,an optically actuated manipulator arm was fabricated to realize grabbing,lifting,and releasing of an object by irradiating the ?finger? shape of the ?hand? under green and UV light.The amipulator arm could grab object which weighed five times of its.The whole process could be repeated 40 times.Micro cracks would be produced during deformation.After irradiated by green laser for 20 s,the minor injuries of finger disappeared.When the the film was cut into two pieces then irradiated by green laser for 10 min,the temperature reached to 65oC.The stress recovered to 98% of initial stress.The self-healing performance of PAA-u/t-Azo film is better than most hydrogen bond healing system.In this paper,supramolecular assembly based on multiple H-bonds has good controllability,stability and fast self-healability.It could be used as optically actuated manipulator arm which broadens the development of supramolecular assemblies system based on multiple hydrogen bonds.