Zi-Kang Zhu

Preparation of polychrome silver nanoparticles in different solvents

Polychrome silver nanoparticles have been prepared by a soft solution approach under microwave irradiation from a solution of silver nitrate (AgNO3) in the presence of poly(N-vinyl-2-pyrrolidone) without any other reducing agent. Different morphologies of silver colloids with charming colors could be obtained using different solvents as the reaction medium. The structures of the silver colloids were determined by X-ray powder diffraction. UV-Vis spectroscopy was used to follow the reaction process and to characterize the optical properties of the resultant silver colloids. The influence of the solvent on the morphology of silver was investigated.

Poly(etherimide)/montmorillonite nanocomposites prepared by melt intercalation: morphology, solvent resistance properties and thermal properties

Polyimide-MMT (montmorillonite) nanocomposites has been prepared by melt blending an organo-modified MMT with a thermoplastic poly(etherimide) (PEI) in an internal mixer. The dispersion of the MMT layers within the PEI matrix was verified using X-ray diffraction and transmission electron microscopy, revealing an exfoliation morphology. Owing to the molecular dispersion of the MMT layers and the strong interaction between PEI and MMT, the nanocomposites exhibited a substantial increase at glass transition temperature and thermal decomposition temperature, and a dramatic decrease in solvent uptake compared to the virgin PEI.

Preparation and properties of hybrids of organo-soluble polyimide and montmorillonite with various chemical surface modification methods

Abstract Montmorillonite (MMT)/Organo-soluble polyimide (PI) hybrids were prepared using a monomer solution intercalation polymerization method. The organo-soluble polyimide was based on pyromellitic dianhydride and 4,4′-diamino-3,3′-dimethyldiphenylmethane. The MMT was organo-modified with three types of intercalation agents: amino acids, primary aliphatic amines and quaternary ammonium salt. The dispersion behavior of MMT in organic solvents and polyimide depends on the type of the functional group and the bulky group of the intercalation agent. The MMT modified with 1-hexadecylamine is observed to possess the best dispersion behavior. The properties of a MMT/PI hybrid are also greatly dependent upon the dispersion behavior of MMT particles. When the MMT is well dispersed, a MMT/PI hybrid would possess desired properties such as strengthening and toughening at the same time, improved thermal stability, decreased thermal expansion coefficient, retaining of the solubility of the polyimide matrix and high optical transparency.

Preparation and properties of organosoluble polyimide/silica hybrid materials by sol–gel process

Organosoluble polyimide/silica hybrid materials were prepared using the sol–gel process. The organosoluble polyimide was based on pyromellitic anhydride (PMDA) and 4,4′-diamino-3,3′-dimethyldiphenylmethane (MMDA). The silica particle size in the hybrid is increased from 100–200 nm for the hybrid containing 5 wt % silica to 1–2 µm for the hybrid containing 20 wt % silica. The strength and the toughness of the hybrids are improved simultaneously when the silica content is below 10 wt %. As the silica content is increased, the glass transition temperature (Tg) of the hybrids is increased slightly. The thermal stability of the hybrids is improved obviously and their coefficients of thermal expansion are reduced. The hybrids are soluble in strong polar aprotic organic solvents when the silica content is below 5 wt %.

Silver nanocrystals by hyperbranched polyurethane-assisted photochemical reduction of Ag+

Silver nanoparticles in hyperbranched polyurethane (HP) matrix were prepared by means of UV irradiation at room temperature. HP was found to play a key role in the photochemical reduction of silver ions and the formation of nanosized particles. Transmission electron microscopic (TEM) analysis showed that silver nanoparticles were homogeneously dispersed in HP matrix. The absorption peaks due to the surface plasmon resonance of the obtained silver nanoparticles were observed at about 430 nm in the ultraviolet-visible (UV-Vis) absorption spectra. X-ray powder diffraction (XRD) was also used to characterize the obtained nanoparticles.

Formation of monodispersed PVP-capped ZnS and CdS nanocrystals under microwave irradiation

Abstract Poly ( N -vinyl-2-pyrrolidone) (PVP)-capped ZnS, CdS nanoparticles were prepared by a microwave method from Zn(Ac) 2 or Cd(Ac) 2 and thiourea in N , N -dimethylformamide (DMF) solution. The reaction process was monitored by the temporal evolution of the absorption spectrum. With PVP as stabilizer, monodispersed semiconductor nanoparticles, which showed high quantum size effect, have been obtained. Further study showed that the microwave irradiation could influence selectively the nucleation and growing rates of different semiconductor nanoparticles.

Formation of silver dendrites under microwave irradiation

Well-defined silver dendrites were successfully prepared in DMF solution containing poly(N-vinly-2-pyrrolidone) (PVP) as the stabilizer under microwave irradiation. Morphology similar to those of the DLA model fractal dimensions around 1.7 has been observed in our systems. It was found that microwave power and the existence of PVP played important roles in the formation of well-defined silver dendrites. The products were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The proposed formation mechanism of dendrites was also investigated.

Preparation and properties of organosoluble montmorillonite/polyimide hybrid materials

Organosoluble montmorillonite/polyimide hybrids were prepared using a monomer solution intercalation polymerization method. Montmorillonite was organo-treated with p-aminobenzoic acid and the organosoluble polyimide was based on pyromellitic dianhydride and 4,4′-diamino-3,3′-dimethyldiphenylmethane. The particle size of montmorillonite in the hybrid containing 1 wt % of montmorillonite is about 400 nm. The strength and the toughness of montmorillonite/polyimide hybrids are improved simultaneously when the montmorillonite content is below 5 wt %. The thermal stabilities of montmorillonite/polyimide hybrids are obviously improved and their thermal expansion coefficients are reduced. When the montmorillonite content is below 5 wt %, the montmorillonite/polyimide hybrids are soluble in strong aprotonic polar organic solvents.

Preparation and properties of montmorillonite/organo-soluble polyimide hybrid materials prepared by a one-step approach

Montmorillonite (MMT)/organo-soluble polyimide (PI) hybrids were prepared using a one-step approach. The organo-modified MMT was dispersed in a solution of diphenylether-3, 3′4,4′-tetracarboxylic dianhydride and 4,4′-diamino-3,3′-dimethyldiphenylmethane. The solution polycondensation followed by a direct solution imidization at 180 °C resulted in MMT/PI hybrid solutions. From wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) results, the MMT is basically exfoliated in the hybrid films cast from the solutions when the MMT content is below 5 wt%. Further increase in the MMT content leads to severe aggregation. The properties of a MMT/PI hybrid are significantly dependent upon the MMT content. When the MMT content is below 6 wt%, the introduction of the MMT leads to strengthening and toughening to the PI matrix at the same time. The introduction of the MMT also results in improved thermal stability, marked decrease in coefficient of thermal expansion, slight increase in glass transition temperature and increase in modulus.

Conversion of Cu2O nanocrystals into hollow Cu2−xSe nanocages with the preservation of morphologies

With the use of PVP (polyvinylpyrrolidone) as capping reagent, cubic, octahedral and spherical Cu2O nanocrystals were obtained in aqueous media when different reducing agents were applied. After adding selenium sources at room temperature, these nanocrystals could be converted (based on the Kirkendall effect) into hollow Cu2-xSe nanocages that keep their corresponding orignial morphologies.