The Precise Synthesis And Optical Visualization Of Anisotropic Polymer Microspheres Labeled With Aggregation-Induced Emission Probes

Anisotropic polymer microspheres（APMs）are multifunctional colloidal particles with directional morphology,structure,and properties.This special structure enables the multiple functions to integrate in a single particle.Fluorescent anisotropic polymer microspheres have great application potential in fluorescence imaging,optical sensing,colloidal surfactants and screen display owing to their unique morphology and various functions.However,it is still a challenge to accurately prepare anisotropic polymer microspheres with specific morphology and function.Among the few systematic study of controlled preparation of fluorescent anisotropic microspheres,traditional dyes encapsulated with polymer microspheres often show aggregation-caused quenching（ACQ）.Aggregation-induced emission luminogens（AIEgens）have the properties of aggregation-enhanced fluorescence,which is the ideal chromophores to label anisotropic polymer microspheres.In this paper,a series of anisotropic polymer microspheres with specific morphologies were accurately prepared by seed emulsion polymerization.The asymmetric morphology,structure,interfacial properties,and optical functions were regulated.These anisotropic polymer microspheres were used in invisible inks,colloidal surfactants,and fluorescent visualization.The main research contents of this paper are as follows:1)Preparation of anisotropic polymer microspheres labeled with AIEgens.The crescent shape amphiphilic anisotropic microspheres AIE-APMs were synthesized by seed swelling emulsion interface polymerization using linear polystyrene（PSt）colloids as seeds,styrene（St）and acrylic acid（AA）as monomers and divinylbenzene（DVB）as crosslinking agents.The optical properties of polymer microspheres are systematically studied.Due to the encapsulation of AIEgens(1.3×10^-2 mg/mg),the microspheres fluoresceed blue and sensed to different solvents.The morphology of microspheres changed from crescent-like to spherical-like with the amount of AIEgens,hydrophilic and hydrophobic monomers,and crosslinking agents.The internal hierarchical structure of AIE-APMs was studied by transmission electron microscopy（TEM）and super-resolution imaging technology.The invisible inks prepared by these microspheres can be successfully used for pen,pigment pen,seal,and inkjet printing,owing to its good dispersivity and no trace writing on the paper.2)Pickering emulsion polymerization stabilized by AIE anisotropic polymer microspheres.AIE-APMs prepared by the seed swelling emulsion interfacial polymerization method are surface-active colloidal particles,which can stabilize the Pickering emulsion.By adjusting the ratio of water to oil,the emulsion types changed from water-in-oil to oil-in-water.The emulsification behaviors of AIE-APMs in two emulsion states were observed by fluorescence microscope takeing advantage of its fluorescence.Further,the hemispherical microspheres were used as the interfacial stabilizer for Pickering emulsion polymerization to prepare polymer macrospheres.It was found that many factors,such as stirring speed,p H condition,the concentration of hemispherical microspheres,mass ratio of oil phase/microsphere and monomer viscosity,can influence the final particle size and size distribution.Finally,uniform macroscopical polystyrene spheres with particle size ranging from 1 mm to 5 mm were synthesized.3)Controlled preparation of well-defined polymer hemispheres.In order to obtain the anisotropic polymer hemispheres with more elegant morphology,the preparation method was adjusted.Linear polystyrene（PSt）colloids were used as seeds,isobutyl methacrylate（iBMA）and acrylic acid（AA）were used as monomers.The seed swelling emulsion polymerization was carried out,by which the anisotropic polymer spheres.After ethanol washing,the well-defined monodisperse PSt/P（iBMA-co-AA）anisotropic polymer hemispheres were obtained.The morphology evolution of polymer microsphere was investigated by SEM,which was verified that the solvent alcohol was the key to realize the transformation from spherical to hemispherical morphology.According to the analysis of chemical composition by ¹H NMR,the formation of polymer hemispheres was caused by the removal of PSt/P（iBMA-co-AA）in the spheres by alcohol solvent.Moreover,the prepared polymer hemispheres have good morphological stability in strong polar solvents.4)Fluorescent visualization of heterogeneous structure inside anisotropic polymer microspheres and its formation mechanism.In order to further study the heterostructure and formation mechanism of PSt/P（iBMA-co-AA）anisotropic polymer spheres and hemispheres,the AIE probe was used as a new optical visualization tool to characterize the internal structure,interfacial properties,and polymerization process.When the PSt/P（iBMA-co-AA）anisotropic polymer spheres and hemispheres were stained with hydrophilic and hydrophobic dyes at the same microsphere,the fluorescence imaging results showed the anisotropy of fluorescence.The results show that both spheres and hemispheres have a heterogeneous structure with hydrophilic surface and hydrophobic interior.What’s more,the interior of a sphere was differentiates into two hemispheres with different chemical components owing to microphase separation.Superresolution fluorescence imaging technology was introduced to observe the hydrophilic and hydrophobic layers of microspheres,which successfully characterized the microphase structure of the hydrophilic layers,and the resolution was improved by an order of magnitude compared with traditional fluorescence imaging.AIE probe tetraphenylethylene（TPE）was used to trace the morphology evolution process of microsphere and its internal phase separation during the seed emulsion polymerization progress by fluorescent imaging and fluorescent intensity.The microphase separation of a single micron object was successfully observed and tracked.It was found that one half of the microsphere began to show stronger fluorescence than the other half after 30 mins,indicating the occurrence of the phase separation process.The fluorescence intensity of the emulsion tended to be stable after 75 mins,indicating that the emulsion polymerization was closed to completion.Aggregation-induced emission is a powerful method to characterize both the static structure of anisotropic polymer microspheres and the dynamic processes of their formation.