Preparation Of Amphiphilic Gold Nanoparticles At Liquid-liquid Interface And Self-assembly In Solution

Gold nanoparticle (AuNPs) is one of the most stable metal nanoparticles. It hasmany applications in biology and catalysis for its fanscinating size-related electronic,optic, magnetic, and catalytic properties. The structural arrangement of AuNPs playsa key role in device fabrication. In self-assembly process, designed AuNP buildingblocks spontaneously organize themselves into ordered structures througnnoncovalent interactions. Citrate-protected AuNPs allow further chemicalmodification by hydrophobic polymer chains, to obtain amphiphlic hybrid AuNPs.These amphiphlic hybrid AuNPs can segregate at the liquid-liquid interface, andassemble to colloid particles, micelles, vesicles, hollow capsules.1. Colloid particles with polystyrene (PS) cores and AuNPs coronae wereprepared based on self-assembly of AuNPs and PS. Citrate-stabilized AuNPs weredispersed in aqueous solution, and polystyrene with thiol terminal groups (PS-SH)was dissolved in toluene. A stable emulsion was obtained by mixing the twosolutions. Optical microscope images indicate that after grafting of PS-SH to thecitrate-stabilized AuNPs at liquid-liquid interface, the interfacial tension is reducedand the average size of toluene droplets in the emulsion decreases. Transmissionelectron microscope (TEM) results also prove the grafting of PS-SH to AuNPs andlocation of the hybrid nanoparticles at liquid-liquid interface. Colloid particles withPS cores and AuNPs coronae were prepared by addition of the emulsion into excessmethanol. The weight ratio of PS-SH to AuNPs exerts a significant effect on the sizeof colloid particles. TEM and dynamic light scattering results both indicate that thesize of colloid particles increases with the weight ratio. The application of thecore-shell structured colloid particles in protein separation was also investigated inthis research. Colloid particles with PS-coated magnetic nanoparticles in the corescan also be prepared by this strategy.2. PS brushes on Fe3O4nanoparticles were prepared by reversible additionfragmentation chain transfer (RAFT) polymerization, and after reduction reaction PS brushes with terminal thiol groups (HS-PS-Fe3O4NPs) were obtained.Citrate-stabilized AuNPs were dispersed in aqueous solution and HS-PS-Fe3O4NPswere dispersed in toluene. Upon mixing of the two solutions, a stable O/W emulsionwas prepared. Hydrophilic gold nanoparticles interacted with hydrophobic Fe3O4nanoparticles via Au-S interaction at liquid-liquid interface, and amphiphilicnanoparticle complexes were formed at the interface. In methanol, the nanoparticlecomplexes self-assembled into nanoparticles with Fe3O4-nanoparticle cores andgold-nanoparticle coronae. The core-shell structures were still remained in THF.3. PS with pendant hydrophilic AuNPs were synthesized by free radicalcopolymerization of styrene and AuNPs monomer at liquid-liquid interface. Thehybrid polymers can self-assemble into ordered structures in aqueous solutions. Thehydrophilicity of the hybrid polymers plays a key role in the self-assembly of thepolymers. A decrease in the number of hydrophilic AuNPs results in a transitionfrom micellar structure to vesicular structure. After grafting of hydrophilicpoly(N-vinyl pyrrolidone) chains to the pendant AuNPs, the self-assembly changesfrom vesilcular structure to core-shell-corona structure. The hybrid polymers andPS-coated Fe3O4nanoparticles can self-assemble into vesicles with PS andPS-coated Fe3O4nanoparticles in the walls and AuNPs in the coronae, and the sizeof vesicles is determined by the number of pendant AuNPs.4. Amphiphilic AuNPs were produced in situ at liquid-liquid interface via ligandexchange between hydrophilic AuNPs and disulfide-containing polymer chains. Byusing oil droplets as templates, hybrid hollow capsules with AuNPs on the surfaceswere obtained after interfacial cross-linking polymerization. The volume ratio oftoluene to water exerts an important effect on the size of capsules. The average size ofthe capsules increases with the volume ratio. TEM, scanning electron microscopy(SEM) and atomic force microscopy (AFM) were used to characterize the hollowstructures. In this research not only one-component but also multi-component hollowcapsules were prepared by copolymerization of acrylamide and hybrid AuNPs atliquid-liquid interface. Because of the improvement in hydrophilicity of the hollowcapsules, the average size of multi-component capsules is bigger than one-componentones in aqueous solution. 5. Amphiphilic AuNPs were produced in situ at liquid-liquid interface vialigand exchange between hydrophilic AuNPs and disulfide-containing polymerchains. By using oil droplets as templates, hybrid hollow capsules with AuNPs onthe surfaces were obtained after UV cross-linking dimerization. Monomer AnMAwas synthesized by Mitsunobe reaction, DS-PAnMA-co-PMMA was prepared byATRP and disulfide initiator. Citrate-stabilized AuNPs were dispersed in aqueoussolution and DS-PAnMA-co-PMMA was dissolved in toluene. Upon mixing of thetwo solutions, reactive amphiphilic AuNPs were obtained at the liquid-liduidinterface. Anthracene groups were tethered on thesurface of AuNPs, UV light easilycrosslink the reactive amphiphilic AuNPs at liquid-liquid interface to obtain hybridhollow capsules with AuNPs on the surfaces. TEM, fluorescence microscopy andAFM were used to characterize the hollow structures. The distances between AuNPscould be adjusted by changing dispersion medium of hollow capsules.