Nonisothermal crystallization behavior of the poly(ethylene glycol) block in poly(L-lactide)-poly(ethylene glycol) diblock copolymers: Effect of the poly(L-lactide) block length

The confined crystallization behavior, melting behavior, and nonisothermal crystallization kinetics of the poly(ethylene glycol) block (PEG) in poly(L-lactide)poly(ethylene glycol) (PLLA-PEG) diblock copolymers were investigated with wideangle X-ray diffraction and differential scanning calorimetry. The analysis showed that the nonisothermal crystallization behavior changed from fitting the Ozawa equation and the Avrami equation modified by Jeziorny to deviating from them with the molecular weight of the poly(L-lactide) (PLLA) block increasing. This resulted from the gradual strengthening of the confined effect, which was imposed by the crystallization of the PLLA block. The nucleation mechanism of the PEG block of PLLA15000-PEG5000 at a larger degree of supercooling was different from that of PLLA2500-PEG5000, PLLA5000-PEG5000, and PEG5000 (the numbers after PEG and PLLA denote the molecular weights of the PEG and PLLA blocks, respectively). They were homogeneous nucleation and heterogeneous nucleation, respectively.

Deformation mechanism of polystyrene toughened with sub-micrometer monodisperse rubber particles

Core-shell polybutadiene-graft-polystyrene (PB-g-PS) rubber particles with different ratios of polybutadiene to polystyrene were prepared by emulsion polymerization through grafting styrene onto polybutadiene latex. The weight ratio of polybutadiene to polystyrene ranged from 50/50 to 90/10. These core-shell rubber particles were then blended with polystyrene to prepare PS/PB-g-PS blends with a constant rubber content of 20 wt%. PB-g-PS particles with a lower PB/PS ratio (<= 570/30) form a homogeneous dispersion in the polystyrene matrix, and the Izod notched impact strength of these blends is higher than that of commercial high-impact polystyrene (HIPS). It is generally accepted that polystyrene can only be toughened effectively by 1-3 mu m rubber particles through a toughening mechanism of multiple crazings. However, the experimental results show that polystyrene can actually be toughened by monodisperse sub-micrometer rubber particles. Scanning electron micrographs of the fracture surface and stress-whitening zone of blends with a PB/PS ratio of 70/30 in PB-g-PS copolymer reveal a novel toughening mechanism of modified polystyrene, which may be shear yielding of the matrix, promoted by cavitation.

Isothermal crystallization behavior of the poly(L-lactide) block in poly(L-lactide)-poly(ethylene glycol) diblock copolymers: Influence of the PEG block as a diluted solvent

Isothermal crystallization kinetics and morphology of the poly(L-lactide) block in poly(L-lactide)poly(ethylene glycol) diblock copolymers were studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM), respectively. The results were compared with that of the PLLA homopolymer. The introduction of the PEG block accelerated the crystallization rate of the PLLA block and promoted to form ring-banded spherulites. The analysis of isothermal crystallization kinetics has shown that the PLLA homopolymer accorded with the Avrami equation. But the PLLA block of the diblock copolymers deviated from the Avrami equation, which resulted from increasing of the crystallization rate and occurring of the second crystallization process. The equilibrium melting temperature (T,,) of the PLLA block fell with its molecular weight decreasing. The conditions to obtain more regular ring-banded spherulites were below: the sample was the PLLA block of LA(5) EG(5); the crystallization temperature was about from 95 degrees C to 100 degrees C, which almost corresponded to regime II.

Electrochemical Metalloimmunoassay Based on Enlargement of Gold Nanoparticle Label Treated with Ag Enhancement System

A novel sensitive electrochemical immunoassay with colloidal gold as the antibody labeling tag and subsequent signal amplification by silver enhancement is described. Colloidal gold was treated by a light-sensitive silver enhancement system which made silver deposit on the surface of colloidal gold(form Au/Ag core-shell structure), followed by the release of the metallic silver atoms anchored on the antibody by oxidative dissolution of them in an acidic solution and the indirect determination of the dissolved Ag+ ions by anodic stripping voltammetry(ASV) at a carbon fiber microelectrode. The electrochemical signal is directly proportional to the amount of analyte(goat IgG) in the standard or a sample. The method was evaluated by means of a noncompetitive heterogeneous immunoassay of immunoglobulin G(IgG) with a concentration as low as 0.2 ng/ mL. The high performance of the method is related to the sensitive ASV determination of silver(I) at a carbon fiber microelectrode and to the release of a large number of Ag+ ions from each silver shell anchored on the analyte(goat IgG).

Computer simulation of miscibility and self-assembly structure for polymer-containing systems with special interactions

The miscibility and structure of A-B copolymer/C homopolymer blends with special interactions were studied by a Monte Carlo simulation in two dimensions. The interaction between segment A and segment C was repulsive, whereas it was attractive between segment B and segment C. In order to study the effect of copolymer chain structure on the morphology and structure of A-B copolymer/C homopolymer blends, the alternating, random and block A-B copolymers were introduced into the blends, respectively. The simulation results indicated that the miscibility of A-B block copolymer/C homopolymer blends depended on the chain structure of the A-B copolymer. Compared with alternating or random copolymer, the block copolymer, especially the diblock copolymer, could lead to a poor miscibility of A-B copolymer/C homopolymer blends. Moreover, for diblock A-B copolymer/C homopolymer blends, obvious self-organized core-shell structure was observed in the segment B composition region from 20% to 60%. However, if diblock copolymer composition in the blends is less than 40%, obvious self-organized core-shell structure could be formed in the B-segment component region from 10 to 90%. Furthermore, computer statistical analysis for the simulation results showed that the core sizes tended to increase continuously and their distribution became wider with decreasing B-segment component.

Self-assembly of star block copolymers by dynamic density functional theory

The dynamic mean-field density functional method, driven from the generalized time-dependent Ginzburg-Landau equation, was applied to the mesoscopic dynamics of the multi-arms star block copolymer melts in two-dimensional lattice model. The implicit Gaussian density functional expression of a multi-arms star block copolymer chain for the intrinsic chemical potentials was constructed for the first time. Extension of this calculation strategy to more complex systems, such as hyperbranched copolymer or dendrimer, should be straightforward. The original application of this method to 3-arms block copolymer melts in our present works led to some novel ordered microphase patterns, such as hexagonal (HEX) honeycomb lattice, core-shell HEX lattice, knitting pattern, etc. The observed core-shell HEX lattice ordered structure is qualitatively in agreement with the experiment of Thomas [Macromolecules 31, 5272 (1998)].

Improved size control of large palladium nanoparticles by a seeding growth method

A new approach to the preparation of large palladium nanoparticles with diameters between 25 and 100 nm is presented. In this approach PdCl42- ions are reduced on the surface of performed 12-nm-diameter gold "seeds'' by the introduction of ascorbic acid. The resultant particles exhibit improved monodispersity relative to previous work. Interestingly, these nanoparticles possess Au-Pd core-shell structures. The method can be scaled up to produce 50-110 mg of large palladium nanoparticles.

Characterization of Y2O3 : Eu coated with polystyrene

The core-shell Y2O3:Eu3+/polystyrene particles was prepared by surface modification with citric acid and emulsion polymerization method of styrene. The DTA curve of coated particles exhibits a small and wide exothermic peak of organic compound around 387 degreesC. The carbonyl stretching vibration band was shifted to low wavenumber in FTIR spectrum and the binding energy of Y3d5/2 was shifted to high-energy band in XPS spectrum. The results of FTIR and XPS show that citric acid was coupled to the particles surface. The hydrophilic surface became amphiphilic by modification of citric acid. So styrene could adsorb on particles surface to form emulsion structure which inorganic core was inside. EDS spectra show that Y2O3:Eu3+ particles were coated uniformly with polystyrene.

Synthesis of novel star-like hyperbranched polymers with poly(amido amine) core and poly(L-lysine) shell

Hyperbranched poly(amido amine)s containing vinyl and hydroxyl groups were successfully synthesized via Michael addition polymerization of triacrylamide (TT) and 3-amino-1,2-propanediol (APD) with equal molar ratio in feed. H-1, C-13 and HSQC NMR techniques were used to clarify the structure of hyperbranched polymers and polymerization mechanism.

Fabrication of Iron Oxide Core/Gold Shell Submicrometer Spheres with Nanoscale Surface Roughness for Efficient Surface-Enhanced Raman Scattering

A method to synthesize Fe3O4 core/Au shell submicrometer structures with very rough surfaces on the nanoscale is reported. The Fe3O4 particles were first modified with uniform polymers through the layer-by-layer technique and then adsorbed a lot of gold nanoseeds for further Au shell formation. The shell was composed of a large number of irregular nanoscale An particles arranged randomly, and there were well-defined boundaries between these Au nanoparticles. The Fe3O4 core/Au shell particles showed strong plasmon resonance absorption in the near-infrared range, and can be separated quickly from solution by an external magnet.

Bifunctional nanostructure of magnetic core luminescent shell and its application as solid-state electrochemiluminescence sensor material

Bifunctional nanoarchitecture has been developed by combining the magnetic iron oxide and the luminescent Ru(bpy)(3)(2+) encapsulated in silica. First, the iron oxide nanoparticles were synthesized and coated with silica, which was used to isolate the magnetic nanoparticles from the outer-shell encapsulated Ru(bpy)(3)(2+) to prevent luminescence quenching. Then onto this core an outer shell of silica containing encapsulated Ru(bpy)(3)(2+) was grown through the Stober method. Highly luminescent Ru(bpy)(3)(2+) serves as a luminescent marker, while magnetic Fe3O4 nanoparticles allow external manipulation by a magnetic field. Since Ru(bpy)(3)(2+) is a typical electrochemiluminescence (ECL) reagent and it could still maintain such property when encapsulated in the bifunctional nanoparticle, we explored the feasibility of applying the as-prepared nanostructure to fabricating an ECL sensor; such method is simple and effective. We applied the prepared ECL sensor not only to the typical Ru(bpy)(3)(2+) co-reactant tripropylamine (TPA), but also to the practically important polyamines. Consequently, the ECL sensor shows a wide linear range, high sensitivity, and good stability.

Structure of upper-g(9/2)-shell nuclei and shape effect in the Ag-94 isomeric states

Using a shell model which is capable of describing the spectra of upper g(9/2)-shell nuclei close to the N = Z line, we study the structure of two isomeric states 7(+) and 21(+) in the odd-odd N = Z nucleus Ag-94. It is found that both isomeric states exhibit a large collectivity. The 7(+) state is oblately deformed, and is suggested to be a shape isomer in nature. The 21(+) state becomes isomeric because of level inversion of the 19(+) and 21(+) states due to core excitations across the N = Z = 50 shell gap. Calculation of spectroscopic quadrupole moment indicates clearly an enhancement in these states due to the core excitations. However, the present shell model calculation that produces the 19(+)-21(+) level inversion cannot accept the large-deformation picture of Mukha et al.