Shiyuan Cheng

Biomimetic synthesis of raspberry-like hybrid polymer-silica core-shell nanoparticles by templating colloidal particles with hairy polyamine shell.

The nanoparticles composed of polystyrene core and poly[2-(diethylamino)ethyl methacrylate] (PDEA) hairy shell were used as colloidal templates for in situ silica mineralization, allowing the well-controlled synthesis of hybrid silica core-shell nanoparticles with raspberry-like morphology and hollow silica nanoparticles by subsequent calcination. Silica deposition was performed by simply stirring a mixture of the polymeric core-shell particles in isopropanol, tetramethyl orthosilicate (TMOS) and water at 25 degrees C for 2.5h. No experimental evidence was found for nontemplated silica formation, which indicated that silica deposition occurred exclusively in the PDEA shell and formed PDEA-silica hybrid shell. The resulting hybrid silica core-shell particles were characterized by transmission electron microscopy (TEM), thermogravimetry, aqueous electrophoresis, and X-ray photoelectron spectroscopy. TEM studies indicated that the hybrid particles have well-defined core-shell structure with raspberry morphology after silica deposition. We found that the surface nanostructure of hybrid nanoparticles and the composition distribution of PDEA-silica hybrid shell could be well controlled by adjusting the silicification conditions. These new hybrid core-shell nanoparticles and hollow silica nanoparticles would have potential applications for high-performance coatings, encapsulation and delivery of active organic molecules.

The aggregation of polystyrene-b-poly(ethylene oxide)-b-polystyrene triblock copolymers in aqueous solution

The aggregation of PS4-b-PEO227-b-PS4 triblock copolymer (the PS and PEO are abbreviations of polystyrene and poly(ethylene oxide), and the subscripts represent the degree of polymerization) in aqueous solution was investigated by Nuclear Magnetic Resonance, Fluorescence Probe, and Transmission Electron Microscope techniques. The experimental results showed that the aggregation did occur and the critical concentration for aggregation was about 0.01 g/l. When the concentration of colloid solution was 10 g/l, the spherical aggregate with a highly polydispersity and radii ranging from 100 to 500 nm was observed. The possible structures of primary micelles and micellar aggregates were proposed. Additionally, the aggregation of PS43-b-PEO45-b-PS43 and PS18-b-PEO45-b-PS18 block copolymers was primarily concerned. The spherical aggregates with a certain size distribution were observed by Transmission Electron Microscope.

The “crew-cut” aggregates of polystyrene-b-poly(ethylene oxide)-b-polystyrene triblock copolymers in aqueous media

Abstract In this paper, the “crew-cut” aggregates in aqueous media formed by polystyrene (PS)- b -poly(ethylene oxide) (PEO)- b -PS triblock copolymers were presented. The polymers used are PS 43 - b -PEO 45 - b -PS 43 , and PS 40 - b -PEO 136 - b -PS 40 triblock copolymers (the subscripts are the degree of polymerization). The several factors affecting the aggregation behaviors have been investigated. The multiple morphologies, including vesicles, large compound vesicles, large compound micelles (LCMs), and so on, were obtained by altering the solvents, solvent composition, annealing time, and copolymer composition. The self-assembled aggregates were characterized with a combination of conventional transmission electron microscope and atomic force microscope techniques. It was found that vesicles were formed when making colloids from the PS 43 - b -PEO 45 - b -PS 43 solutions of THF, dioxane, THF–water, and dioxane–water, while LCMs were obtained in the case of preparing aggregates from the copolymer solutions of DMF and DMF–water. In addition, the larger compound vesicles and a few aggregates with the complex structures were observed using neat dioxane and THF as initial solvents, respectively. Also, prolonging the annealing time was favorable to the formation of vesicles. Furthermore, some unclosed vesicles were observed, which suggested that the vesicles were transformed from the bending of lamellae.

Kinetics and mechanism of emulsifier-free emulsion copolymerization: Styrene-methyl methacrylate-acrylic acid system

The emulsifier-free emulsion copolymerization of styrene (St) and methyl methacrylate (MMA) in the presence of functional monomer acrylic acid (AA) was carried out in batch process. The kinetics was investigated in detail using model function, Integrated Gamma Function. The morphology and size of particles were monitored continuously by TEM all along the polymerization. It was found that the nucleation, polymerization rate increase with increasing concentration of the functional monomer AA, initiator ammonium persulfate (APS), and polymerization temperature T, and APS plays a predominant role in the particle nucleation process. The particle nucleation stage ceased at about 10% conversion and the steady stage can be extended to about 70% conversion. The particle nucleation is likely to yield primary particle via the mechanism of homogeneous coagulative nucleation and coagulation of the primary particle to yield uniform particles. The particle growth in the postnucleation stage is via a shell growth mechanism.

Biomimetic synthesis of copolymer-silica nanoparticles with tunable compositions and surface property.

We report using cationic poly(acrylamide-co-2-(dimethylamino) ethyl methacrylate, methyl chloride quaternized) (poly(AM-co-DMC)) to mediate biomimetic synthesis of hybrid copolymer-silica nanoparticles under ambient conditions. Poly(AM-co-DMC)s with various mole contents of DMC were prepared by solution copolymerization in water. Silicification was achieved by simply stirring a mixture of tetramethyl orthosilicate and an aqueous poly(AM-co-DMC) solution at room temperature for 30 min. Copolymers-silica hybrid nanoparticles were characterized with transmission electron microscopy (TEM), FT-IR spectroscopy, (1)H NMR, thermogravimetry and aqueous electrophoresis. TEM studies indicated that the hybrid nanoparticles have well-defined spherical morphology and relatively narrow polydispersity with diameters of less than 50 nm. The compositions and zeta potentials of hybrid nanoparticles could be controlled by simply adjusting compositions of copolymers and solution conditions for silica mineralization. Due to the tunable compositions and surface zeta potentials, these new particles would be expected to have potential applications for controlled delivery, therapeutics and bioimaging.

Miniemulsion copolymerization of styrene and butyl acrylate initiated by redox system at lower temperature-preparation and polymerization of miniemulsion

Miniemulsions of styrene and butyl acrylate with sodium dodecyl sulfate (SDS) as the surfactant and hexadecane (HDE) and cetyl alcohol (HDL) as cosurfac- tants were prepared under high-speed stirring or ultrasonification. Results indicate that the stability of miniemulsions produced with HDE is more stable than that with HDL, when the feeding method, in which the cosurfactant is mixed with monomers, is used. There is an optical ratio ( 1 4) of the surfactant to the cosurfactant for maximum stabilization of the miniemulsions. The miniemulsions prepared by ultrasonification are much more stable than those by high-speed stirring. Also, a stable miniemulsion can be prepared at lower temperature (457C) when homogenizing way of ultrasonification is used. The emulsions were of a droplet-size range common to miniemulsions and some of them exhibited long-term stabilities (3 months). When these emulsions were initiated, particle formation occurred predominantly by monomer droplet nucleation. The effects of temperature, ultrasonification time, ratio of monomers, and concentrations of surfac- tant, cosurfactant, and initiator on the polymerization rate, conversion, and particle size were determined. It was found that the miniemulsion copolymerization of styrene and butyl acrylate with a midial amount of a redox initiator ((NH4)2S2O8/NaH SO3) at lower temperature (457C) can be carried out successfully by using a suitable amount of the surfactant SDS (10 mM) and the cosurfactant HDE (40 mM), when a homogeniz- ing way of ultrasonification is applied. q 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 2029-2039, 1998

Emulsifier‐free emulsion copolymerization of styrene and butyl acrylate with cationic comonomer

Emulsifier-free emulsion copolymerization of styrene (St) and butyl acrylate (BA) in the presence of a cationic functional comonomer, N-dimethyl, N-butyl, N-ethyl methacrylate ammonium bromine (DBMA) was carried out using azobis (isobutyl-amidine hydrochloride) (AIBA) as an initiator. The surface properties of particles were studied by testing the actual value of N + and C + (NH 2 )(NH 2 ) on the surface of the particles and the surface charge density. The copolymer particles were characterized using TEM. The effects of reaction temperature, DBMA content, AIBA content, ionic strength, etc., on the conversion of the monomer and the average diameter (Dw) and number (Np) of copolymer particles were investigated. Under constant ionic strength, the average diameter of copolymer particles (Dw) decreased with increasing AIBA and DBMA concentrations and decreased with increasing reaction temperature also. Moreover, it increased with increasing St content in the monomer feeding. Under a constant concentration of the comonomer and initiator as well as the constant monomer composition, Dw shows a change process of increase-decrease-increase in the ionic strength plot. The polymerization reaction rate increased with increasing the DBMA content, AIBA content, and increasing temperature. The surface charge properties of the particles were mainly decided by the DBMA content, AIBA content, ionic strength, etc. The methods of feeding the monomer affects the morphology, structure, size, and surface charge density of the particles.

Styrene-butyl acrylate-N,N-dimethyl N-butyl N-methacrylamidino propyl ammonium bromide emulsifier-free emulsion copolymerization

Emulsifier-free emulsion copolymerization of styrene (St) and butyl acrylate (BA) in the presence of cationic functional comonomer N,N-dimethyl N-butyl N-methacrylamidino propyl ammonium bromide (DBMPAB) was carried out using azobis(isobutylamidine hydrochloride) (AIBA) as initiator. The surface properties of particles were studied by testing the actual value of -N + ≡ and -C(NH 2 ) 2 + on the surface of particles and the surface charge density. The copolymer particles were characterized by transmission electron microscopy (TEM). The effects of reaction temperature, DBMPAB content, AIBA content, and ionic strength on conversion of monomer, average diameter D w ) and number (N p ) of copolymer particles were investigated. Under constant ionic strength the average diameter of copolymer particles (D W ) decreased with increasing AIBA and DBMPAB concentration, and decreased with rising reaction temperature. At constant concentration of comonomer and initiator and constant monomer composition, D w showed an increasc-decrease-increase with ionic strength plot. The polymerization rate increased with increasing DBMPAB content, AIBA content and rising temperature. The surface charge properties of particles were mainly decided by DBMPAB content, AIBA content, and ionic strength.

A study on PVC/LLDPE blends with solid-state-chlorinated polyethylene as compatibilizer

Chlorinated polyethylene (CPE) prepared by solid-state chlorination was used as compatibilizer for poly(vinyl chloride) (PVC)/linear low-density polyethylene (LLDPE) blends. Effects of CPE molecular structure on stress-strain behaviors, dynamic mechanical properties, and morphologies of PVC/LLDPE blends were studied by using SEM, TEM, DMA, and testing mechanical properties. The results showed that the compatibility of PVC/LLDPE blends was improved with the addition of CPE. Also, adhesion strength between the two phases and mechanical properties of the blends were increased.

Miniemulsion copolymerization of styrene and butyl acrylate initiated by redox system at lower temperature: Reaction kinetics and evolution of particle-size distribution

The kinetics of the miniemulsion copolymerization of styrene (St) and butyl acrylate (BA) initiated by redox initiators, (NH4)2S2O8/NaHSO3, at lower temperature (45°C) was studied. The polymerization rate in miniemulsion copolymerization is lower than that of the corresponding conventional emulsion copolymerization. In regard to the rate of polymerization, the initiator concentration plays a more important role in miniemulsion copolymerization than in conventional emulsion polymerization, while the surfactant concentration has a more important role in conventional emulsion polymerization than in miniemulsion polymerization. These are attributed to their different nucleation mechanisms, which are the same as those found in the miniemul- sion polymerization carried out at higher temperatures. While by eliminating nucle- ation via micelle and ensuring against homogeneous nucleation, miniemulsion poly- merization can be carried out by the sole nucleation mechanism—monomer droplet nucleation—at lower temperature. Because of this, the particles become narrower during the polymerization and, finally, monodisperse polymer particles are obtained. The result of the particle numbers indicated that a continuous nucleation will cease at about 60% conversion.