Miniemulsion-based Synthesis,luminescent Properties Regulation,and Applications Of AIE Polymeric Nanoparticles

Aggregation-induced emission polymeric nanoparticles(AIE-PNPs)with merits of high brightness,excellent photostability,good water dispersibility and biocompatibility,and easy surface functionalization,have exhibited great potential in fit-for-purpose fields,such as chemical sensing,flexible devices,smart textiles,and cell imaging.However,there is still a lack of a simple and efficient method for preparation and surface functionalization of AIE-PNPs,and the underlying effects of polymer matrix on the luminescence behavior of AIE luminogens(AIEgens)are needed to reveal for the efficient regulation for luminescence behavior of AIE PNPs.To address the above issues,an efficient and controllable method for preparing AIE-PNPs based on miniemulsion polymerization technology was established.Furthermore,the evolution of luminescence behavior of dispersed phase during polymerization process was analyzed,and the relationships between the chain structure of matrix polymers and luminescence behavior of AIE-PNPs were constructed to guide the design of the structures of AIE-PNPs for optimizing practical applications performance.The main conclusions of this work are presented as follows:(1)Polystyrene/tetraphenylethylene(PSt/TPE)nanoparticles(NPs)were prepared through encapsulation of TPE via miniemulsion polymerization of styrene(St).The brightness,solid content,particle size,and surface properties could be readily regulated by changing the contents of TPE,monomer ratios,amounts of emulsifier,the types and contents of functional monomer.The variations of photoluminescence behavior of emulsion during polymerization process were investigated,and the results indicated that the fluorescence emission of the emulsion is contributed to the crystalline and amorphous TPE molecules in the dispersed phase,which emission intensities of these two TPE forms increased in equal proportion during the polymerization process.This led to the maximum fluorescence emission wavelength(l_em)remain unchanged,whereas the fluorescence intensity increased along with the reaction process,and its growth rate increased first then decreased with the increase of conversion.(2)The chain structures of matrix polymers affect the existing state and restriction degree of TPE,which determines the photoluminescence behaviors of TPE.The introduction of monomer units with long side chains into the copolymer chain of matrix will hamper the crystallization of TPE molecules,leading to thel_em of polymer/TPE NPs red-shifted.On the other hand,the extra free volume introduced by long,flexible side chains increased the intramolecular mobility of TPE,thus,the fluorescence emission efficiency of polymer/TPE NPs decreased.Compared with the polymer/TPE NPs in the glassy state,the side chain of the matrix polymers in the rubbery state had a more significant influence onl_em,with little effect on fluorescence emission efficiency.(3)Based on the above results,AIE-PNPs with tunable properties could be designed for wide applications.The flexible and un-crosslinked poly(styrene-co-butyl acrylate)/AIEgens(poly(St-co-BA)/AIEgens)NPs based on miniemulsion polymerization could be used as nanocolorants for inkjet printing,and the AIE-PNPs formed a homogeneous continuous film on the surface of cotton fibers.The printed fabrics displayed a bright and high-quality pattern under UV light.Furthermore,the developed rigid and highly cross-linked poly(divinylbenzene-co-(4(?)-tetraphenyletheyl)pheny-3-butenylether)(poly(DVB-co-TPE-PBE))NPs could be used as fluorescent sensors for efficient,sensitive,and quantitative detection of picric acid(PA)in aqueous solutions directly.The poly(DVB-co-TPE-PBE)NPs could preserve the original nanostructure,and would not form a continuous film when being coated on the solid substance,which endowed the film with fast response and strong quenching ability to nitroaromatic compound solution and vapor.In summary,this paper established and perfected a facile method for efficient and controllable preparation of AIE-PNPs via miniemulsion polymerization,and the influence factors and regulation mechanism of luminescence behaviors of AIE-PNPs were fully analyzed and revealed.It opens an avenue to facile design and broadens applications of AIE-PNPs.The preparation method and regulation mechanism provided in this paper are universal and extendable,and the superiority has been verified in the applications of inkjet printing and explosives detection.