Synthesis Of Photo-responsive Janus Particles Satellite-like Structure Self-assembly By Azobenzene/cyclodextrin Host-guest Interaction

Particles with chemical or physical asymmetry surface are called Janus macro/nanoparticles.Stimuli-responsive Janus micro/nanoparticles are attractive due to the reversible and inhomogeneous change of surface properties under controlling of external stimuli.However,Janus micro/nanoparticles with switchable physical structure under external stimuli（especially light irradiation）are still lacked.In the past few years,it is an active research field that applying the host-guest chemistry of molecular recognition to synthesize new materials.The simplest method is introducing host/guest molecules to modify the surface of materials.Then,the modified host and guest materials are placed in the same solvent environment,and new materials with molecular recognition effect are formed by the interaction of host and guest.Cyclodextrins（CDs）and azobenzenes（Azos）are the most common host and guest molecules respectively.The research on formation of host-guest complex of the two molecules is also most mature.Trans Azo can be inserted into the hydrophobic cavity ofα-cyclodextrin（α-CD）to form the stable 1:1 host-guest complex,while cis Azo can not.As a kind of photoresponsive guest molecule,the molecular configuration of Azo will change under the irradiation of different wavelength light,which can affect the performance of materials.In this work,azobenzene compounds（Azo-SH and Azo-IPTS）were synthesized by chemical reactions.Under the condition of vacuum,chromium and gold particles were evaporated and deposited on the surface of the upper hemisphere of SiO₂ micro-particles.The SiO₂/Au-Azo Janus microparticles were fabricated by surface modification with azobenzene（Azo）group of Azo-SH on the surface of the microparticles.Then the SiO₂ nanoparticles was prepared by immobilization of Azo group of Azo-IPTS on nanoparticles surface.In order to construct Azo/α-CD host-guest complex,the important host polymer PAA-α-CD molecule was prepared by introducingα-cyclodextrin（α-CD）onto polyacrylic acid（PAA）backbone.In the initial state,Azo mainly exists in the configuration of trans,and with the help of Azo/CD host-guest interaction,Janus micro-nano particles satellite-like structure can be formed between SiO₂/Au-Azo Janus microparticles and SiO₂-Azo nanoparticles.UV light irradiation deformed the satellite-like structure,due to the trans-to-cis isomerization of Azo.However,the satellite-like structure can be reformed under green-light irradiation.Therefore,light-controlling of Janus micro-nano particles satellite-like structure self-assembly was realized,which is potential to be applied in photoresponsive self-assembly system,loading and releasing drugs and fabricating precise and order micro-nano 3D structure in the future.