Physico-chemical studies on a wide composition range of low-moisture glucose–fructose mixtures: rates of crystallisation

The crystallisation rates of low-moisture (from 2% to 10% w/w) glucose–fructose mixtures were investigated at a variety of storage temperatures (from 0 to 60 °C). It was found that d -fructose considerably retards the rate of crystallisation. High storage temperatures induced a decrease in the 'threshold' moisture content, which is necessary for the initial nucleation and further development of the glucose and/or fructose crystals. This knowledge of crystallisation rates can be exploited in terms of storage of confectionery products containing d -glucose, d -fructose or both of them, and honey.     

SECONDARY NUCLEATION OF SUCROSE BY FLUID SHEAR IN AQUEOUS SOLUTIONS

The motivation for this work was based on two hypotheses: subcritical nuclei of sucrose may be generated by secondary nucleation using a fluid shear field acting on the surface of a growing seed crystal in aqueous solutions, and a near-dynamic equilibrium distribution of embryos may be attained. These were supported experimentally. The value of a σ-based model parameter, a, was obtained by describing the system by a Boltzman- like distribution model. The number concentration of subcritical nuclei was well described by the model. Despite differences in experimental method and in the basic nature of the solute, sucrose, the behavior of the system and results were similar to those obtained in the earlier work using aqueous salt solutions [Sung et al. (1973), Jagannathan et al. (1980)].     

Kinetics and particle nucleation mechanism of St/BA/qBVPBr emulsifier‐free cationic emulsion polymerization

Stable functional cationic latices were prepared by emulsifier‐free emulsion copolymerization of styrene (St) and butyl‐acrylate (BA) with 1‐butyl‐4‐vinylpyridinium bromide (qBVPBr) as functional comonomer and azobis(isobutyramidine hydrochloride) (AIBA) as initiator at (70 ± 1)°C. The influences of the reaction temperature, the initiator concentration, and comonomer concentration on the polymerization conversion (x %), polymerization rate (R_p) of poly(St/BA/qBVPBr) emulsions were investigated. The results indicated that x % and R_p increase with increasing qBVPBr or AIBA concentration and temperature, and R_p can be expressed as R_p = K_p[AIBA]^0.73[qBVPBr]^0.08 (r_AIBA = 0.9968; r_qBVPBr = 0.9946, both r_AIBA and r_qBVPBr are linear correlation coefficient) and the apparent activation energy (E_a) is 47.89 kJ mol^?1. In the absence of emulsifier condition, curves of R_p versus reaction time obeyed the typical behavior characterized by Intervals I, II, and III as similar conventional emulsion polymerization. The formation and growth of poly(St/BA/qBVPBr) latex particles has been studied at different reaction times. The results indicate that N_p decrease gradually with time at the early polymerization stages and then reach a constant value after about 20% conversion, but D_p by photon correlation spectroscopy grow continuously as all polymerization proceed. Both the particle size distribution and molecular weight distribution curves are of bimodal size distribution and indicate the participation of at least two mechanisms of particle formation, namely, homogeneous nucleation in the aqueous phase and micellar nucleation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Catalytic electroxidation pathway for the polymerization of polypyrrole in the presence of ultrafine silver nanoparticles

In this work, we report the first electrochemical polymerization of polypyrrole (PPy) on Au substrates in aqueous solutions containing additives of prepared Ag nanoparticles with a diameter less than 2 nm. Due to the effect of Ag nanoparticles, which can provide a catalytic electroxidation pathway for the polymerization of PPy, the synthesized PPy film demonstrates some novel characteristics. It shows a finer and granular raspberry morphology with nano-scaled particles, and a rougher surface. The conductivity of PPy is significantly increased (∼8 times), which also reflects on the extremely high oxidation level of 0.35 revealed from the analysis of X-ray photoelectron spectroscopy (XPS). The mechanism of the nucleation and growth was investigated to explain the specific characteristics of PPy films.     

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 miniemulsion polymerization carried out at higher temperatures. While by eliminating nucleation via micelle and ensuring against homogeneous nucleation, miniemulsion polymerization 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. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 315–322, 1999     

Nanodiamond films deposited at moderate temperature on pure titanium substrate pretreated by ultrasonic scratching in diamond powder suspension

Nanocrystalline diamond （NCD） film deposition on pure titanium and Ti alloys is extraordinarily difficult because of the high diffusion coefficient of carbon in Ti, the large mismatch in their thermal expansion coefficients, the complex nature of the interlayer formed during diamond deposition, and the difficulty to achieve very high nucleation density. In this investigation, NCD films were successfully deposited on pure Ti substrate by using a novel substrate pretreatment of ultrasonic scratching in a diamond powder-ethanol suspension and by a two-step process at moderate temperature. It was shown that by scratching with a 30-μm diamond suspension for 1 h, followed by a 10-h diamond deposition, a continuous NCD film was obtained with an average grain size of about 200 nm. Detailed experimental results on the preparation, characterization, and successful deposition of the NCD films on Ti were discussed.     

Preparation and Characterization of Zinc Aluminosilicate Transparent Glass-Ceramics

Zinc aluminosilicate glasses containing Li2 O, ZnO , Al2O3 and SiO2 were prepared by conventional melting and quenching technique, and subsequently converted to transparent glass-ceramics by controlled nucleation and crystallization. The glass was melted in a platinum crucible at 1 600 ℃ for 2 h and then two-step heat treated for the nucleation and the crystal growth. The nucleation and crystallization temperatures were determined by differential thermal analysis. Specimens heat-treated on different schedules were analyzed by the X-ray diffraction to determine crystalline phases. Scanning electron microscopy was used to study the glass-ceramics morphology, the grain size and distribution in the residual glass matrix. The reorganization of the amorphous solid was confirmed by FT-IR spectroscopy. The transmittance was measured by a UV-Vis-NIR scanning spectrophotometer .     

Microscopic phase-field simulation for nucleation incubation time of Ni75AlxV25-x alloy

With the microscopic phase-field dynamic model, the effects of temperature and concentration on the nucleation incubation time of Ni75AlxV25-x alloy were studied and the relation between the incubation time and precipitation mechanism was investigated by using the atomic occupation probability picture and average order parameter curve. The simulation results demonstrate that there exists the incubation time for different precipitation mechanisms~ such as non-classical nucleation, the mixed style of non-classical nucleation and spinodal decomposition, and spinodal ordering; and the incubation time shortens in turn for the three kinds of mechanisms. With the increase of Al content of Ni75AlxV25-x alloy, the incubation time of Llz phases shortens continuously and that of DOzz phases is prolonged. The effects of temperature on the incubation time of Llz and DOzz phases are accordant, i.e. the incuba- tion time is greatly prolonged with the temperature rising.     

成核添加剂减小冰蓄冷溶液过冷度的实验研究

为了寻求合适的成核添加剂来减小冰蓄冷溶液过冷度和提高结冰速率，建立了冰蓄冷溶液性能测试装置，对含有各种成核添加剂的冰蓄冷溶液在不同环境温度下的凝固结冰过程进行了实验研究。实验结果表明，成核添加剂和环境温度对蓄冷溶液过冷度和结冰速率均有明显影响。对成核添加剂为A的蓄冷溶液，当环境温度为－5.1 ℃时，其过冷度为4.5 ℃，凝固结冰过程耗时165 min；当环境温度为－4.0 ℃时，其过冷度为4.0 ℃，凝固结冰过程耗时410 min。对成核添加剂为B的蓄冷溶液，当环境温度为－4.0 ℃时，其过冷度为2.4 ℃，凝固结冰过程耗时150 min。在冰蓄冷工程中应用加入成核添加剂的蓄冷溶液来提高制冷机运行时的蒸发温度，从而提高制冷机的制冷系数，使空调工程具有更明显的节能效果。