Supramolecular Assemblies Based On Polyelectrolytes For Stimuli-responsive Actuators

Supramolecular assembly based on electrostatic interaction is a facile and effective approach for the preparation of stimuli-responsive composite materials.The responsive properties of the resultant composite materials generally depend on the selection of assembly units.Hence,the design and preparation of novel assembly units is critical for the construction of smart materials.Two types of azobenzenes has been successfully synthesized by Azo coupling reaction and Mills reaction.The photoisomerization studies indicate the absorption properties of the resultant azobenzenes depand 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.However,by o-substitution with F,the stability of cis-isomers can be significantly improved.Moreover,the formation of inter-/intra-molecular hydrogen bond between carboxy group and solvent molecules or N=N can also improve the stability of cis-isomers.The azobenzenes with multi negatively charged groups are ideal building blocks for supramolecular assembly.4-Amino-1,10-azobenzene-3,4'-disulfonic acid monosodiumsalt?AAZO?was uncovalently grafted on the side-chain of poly?diallyldimethylammonium chloride??PDAC?by electrostatic interaction.The free-standing AAZO/PDAC film was obtained by a optimized solution casting method.The X-ray photoelectron spectroscipy?XPS?analysis of AAZO/PDAC film indicates that one AAZO molecule corresponds to 7⁸ structural units in the PDAC chains.This AAZO/PDAC film showed a reversible isomerization irradiated by UV light followed by the reversion with a good cycling stability for 50 cycles.Under UV irradiation,actuators based on AAZO/PDAC films exhibited a large deformation by rolling-up into a tube with double walls.Moreover,the shape deformation of the bending film can be easily fixed and the photomechanical properties of the actuator is stable and reversible.3,3',5,5'-azobenzenetetracarboxylic acid?H₄abtc?was selected for the construction of a supramolecular assembly with PDAC via electrostatic interaction.The XPS analysis of H₄abtc/PDAC film indicates that one H₄abtc molecule corresponds to 18¹9 structural units in the PDAC chains.The H₄abtc/PDAC film showed a reversible isomerization irradiated by UV light followed by the reversion with a good cycling stability for 50 cycles.The fabricated freestanding H₄abtc/PDAC film underwent bending/unbending movements upon treatment with light,humidity,or temperature.Fast rates of shape recovery were achieved for the film on exposure to gently flowing humid nitrogen.The bending/unbending motions are controllable,reversible,and repeatable.A layered nanostructure of lead sulfide?PbS?quantum dot?QD?/multi-walled carbon nanotube?MWNT?hybrid was prepared by the electrostatic assembly after the phase transfer of PbS QDs from an organic to an aqueous phase.Near-infrared absorption of PbS/MWNT nanostructures was improved and efficient charge transfer between PbS and MWNT at the interface resulted in a remarkable quenching of photoluminescence.Two-terminal devices using PbS/MWNT nanostructures showed an excellent on/off switching photocurrent and good stability during 20 cycles under light illumination due to electron transfer from PbS to MWNT.The photoswitch exhibited a high photo sensitivity up to 31.3%with the photocurrent of 18.3?A under the light of 3.85 mW/cm².