Hanying Zhao

Exfoliated graphite oxide decorated by PDMAEMA chains and polymer particles.

Exfoliated graphite oxide (GO) sheets with hydroxyl groups and amine groups on the surface were prepared by modification of graphite. Atom transfer radical polymerization (ATRP) initiator molecules were grafted onto the GO sheets by reactions of 2-bromo-2-methylpropionyl bromide with hydroxyl groups and amine groups. Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) chains on the surface of GO sheets were synthesized by in-situ ATRP. X-ray photoelectron spectroscopy, thermogravimetric analysis, and transmission electron microscopy (TEM) results all demonstrated that polymer chains were successfully produced. After grafting of PDMAEMA, the dispersity of GO sheets in solvents was improved significantly. Poly(ethylene glycol dimethacrylate-co-methacrylic acid) particles were deposited on GO sheets via hydrogen bonding between MAA units on polymer particles and amine groups of PDMAEMA. TEM and scanning electron microscopy were used to characterize the structure of the nanocomposites.

Preparation of reduced graphene oxide/poly(acrylamide) nanocomposite and its adsorption of Pb(II) and methylene blue.

Carboxyl groups at the periphery of reduced graphene oxide (RGO) sheets are converted to amine groups by reaction with N-hydroxysuccinimide and 1,3-diaminopropane, and a free-radical polymerization initiator is anchored to the RGO sheets. Poly(acrylamide) (PAM) polymer brushes on RGO sheets (RGO/PAM) are synthesized by in situ free-radical polymerization. The heavy metals, Pb(II), and the benzenoid compounds, methylene blue, (MB) were selected and adsorbed by RGO/PAM composites, and the adsorption capacity of RGO/PAM for Pb(II) and MB was measured. The experimental data of RGO/PAM isotherms for Pb(II) and MB followed the Langmuir isotherm model. The RGO/PAM displays adsorption capacities as high as 1000 and 1530 mg/g for Pb(II) and MB, respectively, indicating RGO/PAM is a good adsorbent for the adsorption of Pb(II) and MB. The adsorption kinetics of Pb(II) and MB onto RGO/PAM can be well fitted to the pseudo-second-order model. The adsorption processes of Pb(II) and MB onto RGO/PAM are spontaneous at 298, 308, and 318 K.

PS Colloidal Particles Stabilized by Graphene Oxide

Exfoliated graphene oxide (GO) sheets with hydrophilic functional groups on the surface were prepared by the oxidation of graphite. Because of the hydrophilic groups on the sheets and the hydrophobic carbon surface, GO sheets were located at the oil-water interface and could be used as a stabilizer in Pickering emulsions. After the Pickering emulsion polymerization of styrene, PS colloidal particles with GO sheets on the surface were prepared. The size of the GO sheets exerts an important influence on the preparation of PS colloidal particles. Small GO sheets located at the liquid-liquid interface and GO-stabilized PS colloidal particles were prepared; however, for large GO sheets, smaller PS colloidal particles prepared on the GO surface were observed. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the structure and morphology of the colloidal particles. TEM, SEM, and XPS results all suggest the successful preparation of GO-stabilized PS colloidal particles.

Surface-Initiated Free Radical Polymerization at the Liquid―Liquid Interface: A One-Step Approach for the Synthesis of Amphiphilic Janus Silica Particles

Amphiphilic Janus silica particles with hydrophobic polystyrene (PS) and hydrophilic poly(sodium methacrylate) (PSMA) brushes on two hemispheres were prepared at the liquid-liquid interface by surface-initiated polymerization. After introduction of free-radical initiator modified silica particles into a mixture of styrene and water, the silica particles were adsorbed at the liquid-liquid interface. One hemisphere of a silica particle is immersed in aqueous phase, and the other one is in styrene phase. After initiation at an elevated temperature, PSMA chains grow on one hemisphere and PS chains grow on the other one. Thermogravimetric analysis and infrared spectra results confirmed the grafting of polymer brushes on the surfaces. Transmission electron microscopy was used to characterize the asymmetric surface structure and aggregation structure of the Janus particles.

Self-Assembly of Gold Nanoparticles and Polystyrene: A Highly Versatile Approach to the Preparation of Colloidal Particles with Polystyrene Cores and Gold Nanoparticle Coronae

Colloidal particles with polystyrene (PS) cores and gold nanoparticle (AuNP) coronae were prepared on the basis of the self-assembly of AuNPs and PS. Citrate-stabilized AuNPs were dispersed in aqueous solution, and PS with thiol terminal groups (PS-SH) was dissolved in toluene. A stable emulsion was obtained by mixing the two solutions. Optical microscope images indicate that after grafting of PS-SH to the citrate-stabilized AuNPs at liquid-liquid interface, the interfacial tension is reduced and the average size of toluene droplets in the emulsion decreases. Transmission electron microscope (TEM) results also prove the grafting of PS-SH to AuNPs and the location of the hybrid nanoparticles at the liquid-liquid interface. Colloidal particles with PS cores and AuNP coronae were prepared by adding the emulsion to excess methanol. The weight ratio of PS-SH to AuNP exerts a significant effect on the size of colloidal particles. TEM and dynamic light scattering results both indicate that the size of colloidal particles increases with the weight ratio. The application of the core-shell-structured colloidal particles to protein separation was also investigated in this research. Colloidal particles with PS-coated magnetic nanoparticles in the cores were also prepared by this strategy.

Interface-Directed Self-Assembly of Gold Nanoparticles and Fabrication of Hybrid Hollow Capsules by Interfacial Cross-Linking Polymerization

Amphiphilic gold nanoparticles (AuNPs) were produced at liquid-liquid interface via ligand exchange between hydrophilic AuNPs and disulfide-containing polymer chains. By using oil droplets as templates, hybrid hollow capsules with AuNPs on the surfaces were obtained after interfacial cross-linking polymerization. The volume ratio of toluene to water exerts an important effect on the size of capsules. The average size of the capsules increases with the volume ratio. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to characterize the hollow structures. In this research, not only one-component but also multicomponent hollow capsules were prepared by copolymerization of acrylamide and hybrid AuNPs at liquid-liquid interface. Because of the improvement in hydrophilicity of the hollow capsules, the average size of multicomponent capsules is bigger than one-component ones in aqueous solution.

Amphiphilic Asymmetric Comb Copolymer with Pendant Pyrene Groups and PNIPAM Side Chains: Synthesis, Photophysical Properties, and Self-Assembly

An amphiphilic asymmetric comb polymer with pendant pyrene groups and poly(N-isopropylacrylamide) (PNIPAM) side chains was synthesized based on click chemistry and reversible addition-fragmentation chain transfer polymerization. Gel permeation chromatography, FTIR, and (1)H NMR results all indicated successful synthesis of a well-defined comb polymer. The photophysical properties and self-assembly of the polymer in solution were studied by UV-vis spectroscopy, fluorescence technique, and transmission electron microscopy. The intensity ratio of the excimer peak (I(E)) to the monomer peak (I(M)) of the comb polymer in THF was used to monitor the formation of inter- or intramolecular excimers. At low polymer concentration, the value of I(E)/I(M) kept unchanged, indicating the formation of intramolecular excimer; at high polymer concentration, the value increased rapidly with concentration because of the formation of intermolecular excimer. The change of the intensity ratio of the first to the third vibronic band (I(1)/I(3)) on the monomer emission of the comb polymer also proved the association of the pendant pyrene groups in THF at high polymer concentration. In aqueous solution, the comb polymer chains self-assembled into vesicles with pyrene groups in the walls and PNIPAM side chains in the coronae. The value of the critical aggregation concentration of the polymer was determined by fluorescence technique. Temperature exerted a significant effect on the size and morphology of the vesicles. At a temperature above the lower critical solution temperature (LCST) of PNIPAM, PNIPAM brushes in the coronae of vesicles collapsed on the surface of the structures forming nanosized domains, and vesicles with smaller size were obtained. Fluorescence quenching experiments indicated that the collapsed PNIPAM chains protected a part of pyrene groups from being quenched by nitromethane at a temperature above the LCST of PNIPAM.

Amphiphilic gold nanoparticles formed at a liquid–liquid interface and fabrication of hybrid nanocapsules based on interfacial UV photodimerization

In this paper a novel method for fabrication of hybrid hollow capsules based on interface-directed self-assembly of gold nanoparticles (AuNPs) and interfacial photodimerization of anthracene is reported. A hydrophobic random copolymer with a disulfide group at the midpoint and pendant anthracene groups on the repeating units was synthesized by atom transfer radical polymerization. The hydrophobic random copolymer was dissolved in toluene and hydrophilic citrate-stabilized AuNPs were dispersed in water. An emulsion was obtained upon mixing of the two solutions. In the emulsion, hydrophilic AuNPs were able to undergo interface-directed self-assembly and amphiphilic AuNPs were produced at the liquid–liquid interface via ligand exchange. Hybrid nanocapsules with AuNPs on the surfaces were prepared after anthracene photodimerization at the liquid–liquid interface. Transmission electron microscopy, dynamic light scattering, UV-vis and scanning electron microscopy were used to characterize the structure of the hybrid nanocapsules. In the fabrication of the hybrid nanocapsules, the addition of small molecular surfactant has an important effect on the structures. The average size and size distribution of the hybrid nanocapsules can be controlled by controlling the concentration of the small molecular surfactant in the solution, and in the meanwhile the use of the small molecular surfactant will not reduce the surface density of AuNPs on the hybrid nanocapsules. The hybrid nanocapsules display effective catalytic activity in the reduction of 4-nitrophenol by NaBH4.

Silica particles with immobilized protein molecules and polymer brushes.

UNLABELLED In this research thermo-responsive polymer brushes and protein molecules are immobilized on the surfaces of silica particles by covalent bonds. Pyridyl disulfide functionalized silica particles are prepared by surface chemical reactions, and thiol-terminated poly(oligo(ethylene glycol) monomethyl ether methacrylate) (POEGMA) and bovine serum albumin (BSA) molecules are grafted to the silica particles by thiol-disulfide exchange reactions. X-ray photoelectron spectroscopy, thermogravimetric analysis, dynamic light scattering, confocal laser scanning microscopy, far-UV circular dichroism and transmission electron microscopy are employed to characterize the polymer/protein mixed layers on silica particles. The POEGMA brushes not only protect the protein molecules but also improve the dispersibility of the hybrid particles in aqueous solution. The activity of the immobilized BSA protein can be controlled by the thermo-responsive POEGMA brushes. At a temperature below the lower critical solution temperature (LCST) of POEGMA, BSA activity is not affected by polymer brushes; however, BSA activity decreases significantly at a temperature above the LCST of POEGMA. STATEMENT OF SIGNIFICANCE In this research, both protein molecules and polymer brushes were anchored to the silica particles by highly efficient thiol-disulfide exchange reaction, and their grafting density can easily be determined by UV-vis. Owing to the temperature-sensitive nature of the grafted polymer brushes, the protein molecules can be protected by the collapsed polymer brushes above the LCST, and their catalytic activity can be controlled. Moreover, the protein molecules on silica particles can be easily separated from the solution and can be reused.

Controlled self-assembly of amphiphilic monotailed single-chain nanoparticles

In the field of materials science, one of the current challenges is to organize nanoparticles with various sizes, geometries and compositions into specific structures for constructing functional materials and devices. In this research, the self-assembly of the monotailed single-chain nanoparticles with different charge densities was investigated. Poly(2-(dimethylamino)ethyl methacrylate)-block-polystyrene (PDMAEMA-b-PS) was synthesized by reversible addition–fragmentation chain transfer polymerization, and amphiphilic monotailed PDMAEMA single-chain nanoparticles were prepared by intramolecular cross-linking of PDMAEMA blocks. The cross-linking degree was controlled at about 20%. The surface charge densities on the single-chain nanoparticles were controlled by reactions of the single-chain nanoparticles with varying amounts of iodomethane. The surface charge density has a significant influence on the self-assembly of the monotailed single-chain nanoparticles. The monotailed single-chain nanoparticles made from PDMAEMA74-b-PS100 self-assemble into spherical micelles in aqueous solutions, and the average size of the micelles increases with the charge density. With an increase in the charge density, the morphology of the aggregates self-assembled by the monotailed single-chain nanoparticles changes from spherical micelles to vesicles, and to a mixture of worm-like cylinders and vesicles. In a cyclohexane–THF mixture, the monotailed single-chain nanoparticles made from PDMAEMA74-b-PS297 self-assemble into bunchy micelles, or a mixture of vesicles and large compound vesicles, depending on the charge densities.