DEFORMATION OF SOFT COLLOIDAL CRYSTALLINE STRUCTURE - THEORETICAL CONSIDERATIONS AND EXPERIMENTAL EVIDENCES BY SYNCHROTRON SMALL-ANGLE X-RAY SCATTERING ON TENSILE STRETCHED POLYMERIC LATEX FILM

Films obtained via drying a polymeric latex dispersion are normally colloidal crystalline where latex particles are packed into a face centered cubic (fcc) structure. Different from conventional atomic crystallites or hard sphere colloidal crystallites, the crystalline structure of these films is normally deformable due to the low glass transition temperature of the latex particles. Upon tensile deformation, depending on the drawing direction with respect to the normal of specific crystallographic plane, one observes different crystalline structural changes. Three typical situations where crystallographic c-axis, body diagonal or face diagonal of the fcc structure of the colloidal crystallites being parallel to the stretching direction were investigated.

Influence of metal particle size on the hydrogenation of maleic anhydride over Pd/C catalysts in scCO(2)

Hydrogenation of maleic anhydride (MAH) with Pd/C catalysts in supercritical carbon dioxide (scCO(2)) was investigated. The selectivity for gamma-butyrolactone (GBL) reached 97.3% in scCO(2) at 100% conversion of MAH, which was notably higher than that of 77.4% obtained in organic solvent of ethylene glycol dimethyl ether (EGDME). The particle size of Pd exhibited large influence on the reaction rate and selectivity of GBL. Higher selectivity of GBL was obtained with Pd/C catalyst of smaller Pd particle size, and the rate of GBL selectivity increase as a function of CO2 pressure was found to be significantly correlated with Pd particle size.

Particle Size-Dependent Charge Ordering and Magnetic Properties in Pr0.55Ca0.45MnO3

A series of Pr0.55Ca0.45MnO3 compounds with average particle size ranging from 2000 to 30 nm have been synthesized by the sol-gel method and their charge ordering (CO) and magnetic properties are investigated. It is observed that with particle size decreasing, the CO transition is gradually suppressed and finally disappears upon particle size down to 35 nm, while the ferromagnetism (FM) emerges and exhibits a nonmonotonous variation with a maximum at 45 nm samples. The FM components in all samples never reach long-range ordering but rather only show short-range clusters. A new explanation considering the coupling between lattice, charge, and spin in the system is raised to understand the suppression of the CO state, Both the competition between the CO/AFM and FM states and the core-shell model are employed to explain the variation of the FM phase. These results may provide a deeper insight into the physics of particle size effect on the charge ordering manganite.

Brittle-ductile transition of particle toughened polymers: influence of the matrix properties

It was theoretically pointed out that the product of the yield stress and yield strain of matrix polymer that determined the brittle-ductile transition (BDT) of particle toughened polymers. For given particle and test condition, the higher the product of the yield stress and the yield strain of the matrix polymer, the smaller the critical interparticle distance (IDc) of the blends was. This was why the IDc (0.15 mum) of the polypropylene (PP)/rubber blends was smaller than that (0.30 mum) of the nylon 66/rubber blends, and the IDc of the nylon 66/rubber blends was smaller than that (0.60 mum) of the high density polyethylene (HDPE)/rubber blends.

The influence of core-shell structured modifiers on the toughness of poly (vinyl chloride)

The core-shell structured grafted copolymer particles of polybutadiene grafted polymethyl methacrylate (PB-g-PMMA, MB) were prepared by emulsion polymerization. The MB particles were used to modify poly (vinyl chloride) (PVC) by melt blending. The mechanical properties of the PVC blends were investigated. The micro-morphology of the PVC blends was observed by scanning electron microscopy (SEM). The results indicated that the samples with the best impact strength could be obtained when the core-shell weight ratio of PB to PMMA is lower than 93:7, the mechanical properties correlated well with SEM morphologies, the addition of modifier with the ratio core to shell of 93:7 could reduce the domain size of the dispersed phase. Furthermore, the compatibility and properties of the blends were greatly enhanced and improved. The modifier particles could be well dispersed in the PVC matrix.

Non-affine structural evolution of soft colloidal crystalline latex films under stretching as observed via synchrotron X-ray scattering

A polymer dispersion consisting of soft latex spheres with a diameter of 135 nm was used to produce a crystalline film with face-centered cubic (fcc) packing of the spheres. Different from conventional small-molecule and hardsphere colloidal crystals, the crystalline latex film in the present case is soft (i.e., easily deformable). The structural evolution of this soft colloidal latex film under stretching was investigated by in-situ synchrotron ultra-small-angle X-ray scattering. The film exhibits polycrystalline scattering behavior corresponding to fcc structure. Stretching results not only in a large deformation of the crystallographic structure but also in considerable nonaffine deformation at high draw ratios. The unexpected nonaffine deformation was attributed to slippage between rows of particles and crystalline grain boundaries. The crystalline structure remains intact even at high deformation, suggesting that directional anisotropic colloidal crystallites can be easily produced.

Independence of the brittle-ductile transition from the rubber particle size for impact-modified poly(vinyl chloride)

A series of acrylic impact modifiers (AIMS) with different particle sizes ranging from 55.2 to 927.0 nm were synthesized by seeded emulsion polymerization, and the effect of the particle size on the brittle-ductile transition of impact-modified poly(vinyl chloride) (PVC) was investigated. For each AIM, a series of PVC/AIM blends with compositions of 6, 8, 10, 12, and 15 phr AIM in 100 phr PVC were prepared, and the Izod impact strengths of these blends were tested at 23 degrees C. For AIMs with particle sizes of 55.2, 59.8, 125.2, 243.2, and 341.1 nm, the blends fractured in the brittle mode when the concentration of AIM was lower than 10 phr, whereas the blends showed ductile fracture when the AIM concentration reached 10 phr. It was concluded that the brittle-ductile transition of the PVC/AIM blends was independent of the particle size in the range of 55.2-341.1 nm. When the particle size was greater than 341.1 nm, however, the brittle-ductile transition shifted to a higher AIM concentration with an increase in the particle size. Furthermore, the critical interparticle distance was found not to be the criterion of the brittle-ductile transition for the PVC/AIM blends.

Fabrication of a metal particle array based on a self-assembled template from a two-armed polymer

A two-armed polymer with a crown ether core self-assembles to produce macroporous films with pores perpendicularly reaching through the film down to the substrate. A possible assembling mechanism is discussed. The pore size can be conveniently adjusted by changing the solution concentration. These through-hole macroporous films provide a template for fabricating an array of Cu nanoparticle aggregates.

Effect of cavitations on brittle-ductile transition of particle toughened thermoplastics

In this study, we established a correlation between cavitations volume and the brittle-ductile transition (BDT) for particle toughened thermoplastics. The brittle-ductile transition temperature (T-BD) was calculated as a function of T* and interparticle distance (ED), respectively, where T* was a parameter related to the volume of cavitations. The results showed that the smaller the cavitations volume, the higher the brittle-ductile transition temperature. The calculations correlated well with the experimental data. With respect to rubber particle, the rigid particle was too hard to be voided during deformation, thereby the TED of the blend was much higher than that of rubber particle toughened thermoplastic. This was a main reason that rubber particle could toughen thermoplastics effectively, whereas rigid particle could not.

Preparation and application of a novel core-shell-particle-supported zirconocene catalyst

The use of functional groups bearing silica/poly(styrene-co-4-vinylpyridine) core-shell particles as a support for a zirconocene catalyst in ethylene polymerization was studied. Several factors affecting the behavior of the supported catalyst and the properties of the resulting polymer, such as time, temperature, Al/N (molar ratio), and Al/Zr (molar ratio), were examined. The conditions of the supported catalyst preparation were more important than those of the ethylene polymerization. The state of the supported catalyst itself played a decisive role in both the catalytic behavior of the supported catalyst and the properties of polyethylene (PE). IR and X-ray photoelectron spectroscopy were used to follow the formation of the supports. The formation of cationic active species is hypothesized, and the performance of the core-shell-particle-supported zirconocene catalyst is discussed as well. The bulk density of the PE formed was higher than that of the polymer obtained from homogeneous and polymer-supported Cp2ZrCl2/methylaluminoxane catalyst systems. (C) 2001 John Wiley & Sons, Inc.

Effects of rubber content and temperature on unstable fracture behavior in ABS materials with different particle sizes

The fracture behavior of ABS materials with a particle diameter of 110 nm and of 330 nm was studied using instrumented Charpy impact tests. The effects of rubber content and temperature on fracture behavior, deformation mode, stable crack extension, plastic zone size, J-integral value, and crack opening displacement were investigated. In the case of a particle size of 110 nm, the material was found to break in a brittle manner, and the dominant crack mechanism was unstable crack propagation. Fracture toughness increases with increasing rubber content. In the case of a particle size of 330 nm, brittle-to-tough transition was observed. The J-integral value first increases with rubber content, then levels off after the rubber content is greater than 16 wt %. The J-integral value of a particle diameter of 330 nm was found to be much greater than that of 110 nm. The J-integral value of both series first increased with increasing temperature until reaching the maximum value, after which it decreased with further increasing temperature. The conclusion is that a particle diameter of 330 nm is more efficient than that of 110 nm in toughening, but for both series the effectiveness of rubber modification decreases with increasing temperatures higher than 40 degreesC because of intrinsic craze formation in the SAN matrix at temperatures near the glass transition of SAN. (C) 2000 John Wiley & Sons, Inc.

Effect of the core-shell latex polymer content on the compatibility, morphology and mechanical properties of PC/PBA-cs-PMMA blends

The toughening effect of the content of a core-shell poly(butyl acrylate)/poly(methyl methacrylate) latex polymer (PBA-cs-PMMA) on the mechanical properties, morphology and compatibility of its blends with polycarbonate(PC), i.e., PC/PBA-cs-PMMa, was studied. The mechanical properties of the blends are strongly affected by varying the content of PBA-cs-PMMA in the blend. When the PBA-cs-PMMA content is only 5 wt.-%, the impact strength of PC/PBA-cs-PMMA is almost 19 times as high as that of pure PC, indicating that PBA-cs-PMMA is a very good impact modifier for PC. With increasing interphacial layer thickness and decreasing interphacial tension, the interphacial activity becomes more and more effective and, at the same time, miscibility increases too.

Study of the blends containing core-shell latex polymer

Polycarbonate (PC) and a core-shell latex polymer composed of poly(butyl acrylate) and poly(methyl methacrylate) (PBA-cs-PMMA) as core and shell, respectively, were mixed using a Brabender-like apparatus under different conditions. The mechanical properties, the morphology and the processability of the blends were investigated. Because of the good compatibility of PC and PMMA, even dispersion of PBA-cs-PMMA in PC matrix and good adhesion between the components have been achieved. PBA-cs-PMMA is thus a very good impact modifier for PC. The toughening mechanism is both cavitation and shear yielding, as indicated by SEM observation. (C) 1997 Elsevier Science Ltd.