Crystallization Kinetics of Linear and Long‐Chain Branched Polypropylene

Isothermal crystallization kinetics of linear polypropylene (PP) and long‐chain branched (LCB) PPs were investigated on the basis of the Avrami theory. The Avrami exponents of LCB PPs are smaller than that of linear PP; moreover, they decrease with an increasing LCB level. The crystallization half‐time of LCB PP depends more strongly on the crystallization temperature than does that of linear PP. The Lauritzen‐Hoffman theory was used to study the effect of LCB on the crystal growth rate of PP. The fold surface free energy of LCB PP is lower than that of linear PP; moreover, it decreases with an increasing LCB level. However, when the LCB level is over a certain value, the fold surface free energy increases again. Furthermore, the crystal structures of linear PP and LCB PPs were studied by wide‐angle X‐ray diffraction (WAXD); it was observed that linear PP can crystallize in the α and β forms, while LCB PPs have only the α crystalline form. Moreover, the relative intensities of different α peaks were also influenced by the LCB level.     

Reactive Compatibilization of Poly(trimethylene terephthalate)/Polypropylene Blends by Polypropylene‐graft‐Maleic Anhydride. Part 2. Crystallization Behavior

The crystallization behavior of uncompatibilized and reactive compatibilized poly(trimethylene terephthalate)/polypropylene (PTT/PP) blends was investigated. In both blends, PTT and PP crystallization rates were accelerated by the presence of each other, especially at low concentrations. When PP content in the uncompatibilized blends was increased to 50–60 wt%, PTT showed fractionated crystallization; a small PTT crystallization exotherm appeared at ～135°C besides the normal ～175°C exotherm. Above 70 wt% PP, PTT crystallization exotherms disappeared. In contrast, PP in the blends showed crystallization exotherms at 113–121°C for all compositions. When a maleic anhydride‐grafted PP (PP‐g‐MAH) was added as a reactive compatibilizer, the crystallization temperatures (T _c ) of PTT and PP shifted significantly to lower temperatures. The shift of PTT's T _c was larger than that of the PP, suggesting that addition of the PP‐g‐MAH had a larger effect on PTT's crystallization than on PP due to reaction between maleic anhydride and PTT.

The nonisothermal crystallization kinetics was analyzed by a modified Avrami equation. The results confirmed that PTT's and PP's crystallization was accelerated by the presence of each other and the effect varied with blend compositions. When the PP content increased from 0 to 60 wt%, PTT's Avrami exponent n decreased from 4.35 to 3.01; nucleation changed from a thermal to an athermal mode with three‐dimensional growths. In contrast, when the PTT content increased from 0 to 90 wt% in the blends, changes in PP's n values indicated that nucleation changed from a thermal (0–50 wt% PTT) to athermal (60–70 wt% PTT) mode, and then back to a thermal (80–90 wt% PTT) mode. When PP‐g‐MAH was added as a compatibilizer, the crystallization process shifted considerably to lower temperatures and it took a longer crystallization time to reach a given crystallinity compared to the uncompatibilized blends.     

Non‐Isothermal Crystallization Kinetics of PA6/Attapulgite Composites Prepared by Melt Compounding

The non‐isothermal crystallization behaviors of neat polyamide 6 (PA6) and PA6/attapulgite (ATB) composites were examined using differential scanning calorimetry. The results show that ATB acts as a nucleator for PA6 matrix, accelerating the crystallization, and simultaneously obstructs the crystallization especially for the composites with higher ATB content. The analysis results using the Jeziorny and Liu equations verify the dual actions of the nucleation and the obstruction of crystallization of the ATB in the PA6 matrix. Kissinger's method is employed to obtain the activation energy of the crystallization processes; the results further indicate that the addition of ATB may also cause the above actions. It is speculated that there is a very complicated crystallization mechanism in the PA6/ATB composites based on the analysis of Avrami exponents obtained by the Jeziorny model.     

Investigation of the Models of Magnetic Dendrimers by the Wang–Landau Method

Physics of the Solid State - The thermodynamic properties of the models of magnetic dendrimers were studied by the Monte Carlo method. The system state density is calculated; the ground state...     

Non‐isothermal Melt Crystallization Kinetics for Poly(ethylene 2,6‐naphthalate) (PEN)/Montmorillonite Nanocomposites Prepared by Melt Intercalation

The nonisothermal crystallization behaviors for poly(ethylene 2,6‐naphthalate) (PEN) and poly(ethylene 2,6‐naphthalate) (PEN)/montmorillonite nanocomposites prepared by melt intercalation were investigated using differential scanning calorimetry (DSC). The Jeziorny, Ozawa, Ziabicki, and Kissinger models were used to analyze the experimental data. Both the Jeziorny and the Ozawa models were found to describe the nonisothermal crystallization processes of PEN and PEN/montmorillonite nanocomposites fairly well. The results obtained from the Jeziorny and the Ozawa analysis show that the montmorillonite nanoparticles dispersed into PEN matrix act as heterogeneous nuclei for PEN and enhance its crystallization rate, accelerating the crystallization, but a high‐loading of montmorillonites restrain the crystal growth of PEN. The analysis results from the Ziabicki and the Kissinger models further verify the dual actions stated above of the montmorillonite nanoparticles in PEN matrix.     

Determination of the Elemental Composition of Chalcogenide Powders by the X‐Ray Fluorescence Method

A procedure of xray spectral fluorescence analysis of the elemental composition of As _x S_100–x chalcogenide powder samples is developed and its metrological characteristics are established. In determining the content of the components in an As₅₀S₅₀ sample, the relative standard deviation was 0.0030 for As and 0.0035 for S. The results of the xray spectral fluorescence analysis are in good agreement with the data of a gravimetric method.     

Effect of Regrown Graphite on the Growth of Large Gem Diamonds by Temperature Gradient Method

Generally, when growing high-quality large gem diamond crystals by temperature gradient method under high pressure and high temperature, the crystal growth rate is only determined by the temperature gradient. However, we find that the seed crystal cannot completely absorb all the diffused carbon sources, when growing gem diamonds under a higher temperature gradient. Other influence factors appear, and the growth rate of growing diamonds is partly dependent on the crystalline form of superfluous unabsorbed carbon source, flaky regrown graphite or small diamond crystals nucleated spontaneously. The present form is determined by the growth temperature if the pressure is fixed. Different from spontaneous diamond nuclei, the appearance of regrown graphite in the diamondstable region can retard the growth rate of gem diamonds substantially, even if the temperature gradient keeps unchanged. On the other hand, the formation mechanism of metastable regrown graphite in the diamond-stable region is also explained.     

Temperature‐Triggered Capture of Dispersed Particles Using a Laponite‐Poly(NIPAM) Temperature‐Responsive Surface

In this study a new method is investigated that enables a conductive surface to be modified so as to capture dispersed particles when the temperature is increased. Poly(NIPAM) (NIPAM is N‐isopropylacrylamide) was grafted from electrodeposited Laponite RD particles using surface‐initiated atom transfer radical polymerization (ATRP) to give a temperature‐responsive surface. This was used to capture dispersed polystyrene particles. In the first part of the study the conditions used to electrodeposit Laponite onto a carbon foam electrode were determined. The ability of the temperature‐responsive surface to capture dispersed polystyrene particles was investigated between 20 and 50°C. Temperature‐triggered particle capture was reversible or irreversible depending on the conditions used during ATRP. A high surface concentration of poly(NIPAM) on the particle electrodes is believed to increase the extent of polystyrene particle capture and also reversibility. A theoretical analysis in terms of interaction energy–distance curves is presented for the capture behavior. It is concluded that the temperature‐responsive surface has both electrostatic and steric contributions to the total interaction energy. The steric component (which originates from poly(NIPAM)) is temperature‐dependent and provides the basis for temperature‐triggered particle capture.     

Luminescence of GaN Layers Grown on GaAs Substrates by the Method of Radical‐Beam Epitaxy

We have investigated the properties of GaN films obtained by the method of radicalbeam gettering epitaxy. At room temperature the photoluminescence spectra display a weak peak at 3.37 eV, with the fundamental radiation band being located in the range 1.7–2.0 eV. At the temperature 4.2 K, the band with an energy of 3.47 eV is present. The donoracceptor transition with a maximum at 3.26 eV and its phonon repetition dominate in the spectrum. A wide yellow band with a maximum at 2.10 eV and a weak peak at 2.88 eV are also observed. It has been established by Auger electron spectroscopy that gallium and nitrogen are the basic elements that enter into the composition of the film. Xray structural investigations have shown that the films possess a hexagonal structure.     

Synthesis and Thermal Behavior of Silica‐Graft‐Polypropylene Nanocomposites Studied by Step‐Scan DSC and TGA

Silica graft poly(propylene) (silica‐g‐PP) nanocomposites were successfully prepared by radical grafting copolymerization and ring‐opening reaction. Their thermal properties were studied by step‐scan differential scanning calorimetry (SDSC) and thermogravimetric analysis (TGA). The exothermic peaks in the IsoK baseline (C_p,IsoK, nonreversing signal) of SDSC reveal that PP and silica‐g‐PP nanocomposites undergo melting‐recrystallization‐remelting during heating. The peak temperatures of recrystallization and remelting shift upward with the existence of nanoparticles in the PP matrix. The thermal degradation kinetics of silica‐g‐PP nanocomposites were investigated using nonisothermal TGA and the Flynn‐Wall‐Ozawa method. The results indicate that the thermal stability was significantly improved with increasing silica content, mainly because of the physical‐chemical adsorption of the volatile degradation products on the nanoparticles that delays their volatilization during decomposition, and the covalent interaction between nanoparticles and PP chains, which will also reduce the breakage of PP backbone chains.     

Can Nano-Particle Melt below the Melting Temperature of Its Free Surface Partner?

The phonon thermal contribution to the melting temperature of nano-particles is inspected. The discrete summation of phonon states and its corresponding integration form as an approximation for a nano-particle or for a bulk system have been analyzed. The discrete phonon energy levels of pure size effect and the wave-vector shifts of boundary conditions are investigated in detail. Unlike in macroscopic thermodynamics, the integration volume of zero-mode of phonon for a nano-particle is not zero, and it plays an important role in pure size effect and boundary condition effect. We find that a nano-particle will have a rising melting temperature due to purely finite size effect; a lower melting temperature bound exists for a nano-particle in various environments, and the melting temperature of a nano-particle with free boundary condition reaches this lower bound. We suggest an easy procedure to estimation the melting temperature, in which the zero-mode contribution will be excluded, and only several bulk quantities will be used as input. We would like to emphasize that the quantum effect of discrete energy levels in nano-particles, which is not present in early thermodynamic studies on finite size corrections to melting temperature in small systems, should be included in future researches.     

Control of Semiquantum Chaos by the Nonfeedback Method

We numerically study the dynamic behaviour of coupled chaotic oscillators in a so-called semiquantum chaotic system in which one is classical and the other is quantum mechanical.Fourier spectra of the classical oscillator and the ground-state wavefunction of the quantum part have been investigated,when small pulse perturbations are applied.It is found that semiquantum chaos can also be successfully controlled by the nonfeedback method.     

Mathematical Simulation of the Process of Growing a CdTe Single Crystal by the Obreimov–Shubnikov Method

Physics of the Solid State - For the first time, the process of growing a CdTe crystal by the modified Obreimov–Shubnikov method using the technique of self-nucleation from the initial...     

Optical Properties of SiO2 Films Obtained by the Sol‐Gel Method in the Presence of Modifiers of Different Nature

The degrees of hydrolysis of tetraethoxysilane (TEOS) in filmforming compositions containing hydrolysis catalysts and modifiers of different nature have been determined. The TEOS hydrolysis depth has been estimated by the IR spectroscopic method. It is shown that the optical absorption of films depends on the amount of the immobilized indicator and the initial conditions for film formation.     

Growth of Zinc Oxide Thornballs by a Novel Method

Thornballs of zinc oxide (ZnO) is firstly synthesized by a simple solid vapour deposition process under lead oxide (PbO) atmosphere. The micro-thornballs were constituted by numerous needles, which extend outwards in all directions symmetrically. The balls have the dimensions of 120μm in diameter, while the average diameter of the needles was about lO0-200nm. The needles on the balls grow along the (0001) orientation and have gradient cross-sectional radii. Control experiments proved that PbO plays an important role in the growth. The excitationemission measurement exhibits that the synthesized ZnO thornballs possess intensive photoluminescence property, which provides the evidence that PbO does not deteriorate the optical properties of ZnO thornballs.     

Numerical Modelling of Velocity and Temperature Distributions of the Buoyancy Convection Effect in KNbO3 Melt

Numerical Modelling of velocity and temperature fields in high-temperature KNbO3 melt of a loop-shaped Pt wire heater is carried out by using the commercial computational code ANSYS for the mathematical solution of the governing equations.Based on the experimental boundary conditions and the Boussinesq approximation,the numerical modelling of a steady and two-dimensional model is applied to study the process under consideration of the buoyancy-driven convection condition.The result is compared with the previous experimental and theoretical data obtained in our laboratory,and the former is in agreement with the latter.Thus a theoretical guide for reasonable growth conditions is provided by studying in depth the real fluid flow effects in the crystal growth from the melt.     

Dependence of Growing High-Quality Gem Diamonds on Growth Rates by Temperature Gradient Method

Using the temperature gradient method under high pressure and high temperature, we investigate the dependence of growing high-quality gem diamond crystals on the growth rates. It is found that the lower the growth rate of gem diamond crystals, the larger the temperature range of growing high-quality gem diamond crystals, and the easier the control of temperature. In particular, when growing gem diamonds under a very-low growth rate, the temperature range of growing high-quality gem diamonds can extend from a low-temperature pure {100} growth region to {100} {111} growth regions, and finally to a high-temperature only-{111}-growth region. When growing gem diamonds under a high growth rate, some metal inclusions in the growing diamonds always exist near the seeds, no matter whether the growth temperature is high or low. This result is not in agreement with the result of Sumitomo Electric Corporation in Japan.     

Determination of the Local Parameters of a Cascade‐Arc Plasma by the Profiles of the Lines in the Radiation Spectrum

The transverse distribution of the plasma temperature in the positive column of a d.c. cascade arc in argon at atmospheric pressure has been measured. The measurements have been carried out by the conventional method involving the determination of the emissivity of plasma as well as directly from the radiation spectrum of the arc without recourse to the Abelian inversion. A theoretical and model justification of the applicability of the second method is given. The results of the determination of the temperature profile in the observation direction by the width and shift of the ArI 425.9nm line selected for the diagnostics are presented. An analysis of the data obtained supports the possibility of determining the temperature of an inhomogeneous, optically thin plasma from the profiles of lines in the emission spectrum.     

Time-Resolved Investigation of Ionization of Clusters Irradiated by a Strong Laser

Ionization dynamics of clusters irradiated by chirped femtosecond lasers is investigated by using a linearly chirped pulse spectral interferometry with a time resolution of less than lOOfs. The production of an average charged-Xe^18 and -Kr^9 ions indicates a strong energy coupling between laser and cluster. Ultrafast depletion of the probing laser is observed to be strictly coincident with the ionization front as seen in other experiments. Moreover,a two-step ionization process for Xe and Kr clusters irradiated by high-intensity lasers has been observed, which implies the role of resonance enhancement during the cluster explosion.     

Synthesis and Optical Properties of Films Formed by the Sol‐Gel Method in Mesoporous Matrices

The main laws governing the formation of films by the solgel method in the mesopores of anodic aluminum oxide, porous silicon, and synthetic opals have been considered. Investigations of the luminescence at 1.5 m in the structure porous silicon–gel, doped with erbium, have been analyzed. Special features of the synthesis of the film structure microporous xerogel–mesoporous anodic aluminum oxide, doped with erbium, terbium, and europium, and the possible factors that enhance the photoluminescence of lanthanides in the structure are shown.