Characterization and study of microwave activation effects on the polystyrene tacticity

¹³C Nuclear magnetic resonance proved to be an advantageous tool to determine the stereoregularity of polystyrene polymers. The latter was achieved through the analysis of the signal of the quaternary carbon and that of the carbon-p in the aromatic ring too. Styrene was polymerized through microwaves and conventional heating activation using two different polymerization techniques: emulsion and bulk. Microwave activation was performed in a mono-modal type device under the following experimental conditions: various initiator concentrations, an average irradiation power of 50?W, temperature of 70°C, and using a batch reactor for emulsion and bulk experiments. The results obtained in these experiments were compared with those obtained by conventional heating activation polymerization under the same initiator concentration and temperature conditions. Microwave-activated reactions resulted in shorter reaction times and higher yields. The tacticity of the polymer samples was not significantly altered, which lead to the conclusion that, in this case, the stereoregularity of polystyrene was not influenced by microwave irradiation.     

New insights into the impact toughness of ASA (acrylonitrile-styrene-acrylate) with controllable core–shell structure synthesized by three-stage seeded emulsion polymerization

Acrylonitrile-styrene-acrylate (ASA) with controllable core–shell structure was prepared through three-stage seeded emulsion polymerization. A series of characterizations had been performed to study the effect of different core–shell ratios on the properties of ASA. The most interesting was that the impact strength of ASA exhibited a “wave” variation instead of a linear variation with the increasing loading content of poly(butyl acrylate) (PBA) core. Moreover, the threshold of impact strength appeared at 49.725?wt% PBA content, nearly 33 kJ/m². To explain this unusual variation, an impact schematic was proposed.     

一步乳液聚合法制备高溶解性导电聚苯胺

报道了一种高溶解性导电聚苯胺(PANI)的制备方法,以聚2-丙烯酰胺-2-甲基丙磺酸(PAMPS)作为掺杂酸和乳化剂,利用其特有的长链、亲水性及强酸性基团效应,通过乳液聚合法一步合成出具有较高溶解性的导电聚苯胺。利用核磁共振光谱仪(NMR)、傅里叶红外光谱仪(FT-IR)和扫描电子显微镜(SEM)等技术手段对产物结构和性能进行了表征分析。结果表明,在m(苯胺)∶m(AMPS)∶m(APS)=1∶2∶1.5;AMPS质量分数为20%;APS质量分数为30%;反应时间为5 h;反应温度为5℃的条件下,聚苯胺的产率高达86%,在有机溶剂二甲基甲酰胺(DMF)中的溶解度可达0.3814 g/g,在水中的溶解度可达0.2123 g/g,电导率达5.9 S/cm。     

Influence of HPAM on W/O emulsion separation properties

The present study reports on the influence of partially hydrolyzed polyacrylamide (HPAM) on essential w/o emulsion properties. The characterization has been undertaken with low field NMR to follow droplet sizes and distributions, sedimentation and coalescence kinetic, bench-scale electrocoalescence (E_crit) experiments to follow emulsion stability changes, and electrorheology to detect changes in the viscosity upon applying an external electric field. The result is that HPAM does not basically influence the droplet size distribution (DSD) and the stability level of the emulsions as can be expected of bulk polymers. However, there seems to be an interaction between added demulsifiers either through direct molecular interaction or via an interfacial complexation.     

Effect of emulsification processes on the stability of Pickering emulsions stabilized by organomontmorillonites

In this paper, effect of emulsification processes on the properties of Pickering emulsions stabilized by organomontmorillonites (OMts) was studied. Results of micro-morphology and X-ray diffraction showed that the structure of OMt in emulsion depended on the emulsification processes and had an effect on the stability of emulsion. We propose a schematic diagram to reveal the relationship between emulsification processes-OMt laminates structure-stability of Pickering emulsion. In emulsion prepared by ultrasonic, OMt showed uniform dispersion, loose structure, and irregular crystalline. In emulsion prepared by vortex mixing method, OMt illustrated stacking and coagulation structure. In emulsion prepared by microwave method, OMt showed interacting structure and had a little interaction with oil/water interface, and thus the properties of emulsion prepared by microwave was weakly related to oil/water ratios. Emulsification processes had a profound effect on the structure of OMt and stability of Pickering emulsion, which can be used as a trigger to prepare emulsion for various applications.     

Crosslinking network structure governing particle shape and size distribution by one-step emulsion polymerization in the presence of particle coagulation

In this study, sub-200?nm, crosslinked latex particles with a narrow particle size distribution were prepared by one-step emulsion polymerization in the presence of particle coagulation. The relationship between the particle shape and particle coagulation was investigated by varying the time of crosslinking network structure formation and particle coagulation. Particles with irregular shapes such as doublet, triplet, and ellipsoid were obtained using divinylbenzene (DVB) and ethylene glycol dimethacrylate (EGDMA) as the crosslinking agents, because the crosslinking network structure of particles was formed before the particle coagulation. In contrast, latex particles with a uniform spherical shape were also prepared using triallyl isocyanurate (TAIC) or dihydrodicyclopentadienyl acrylate (DCPA) as the crosslinking agents by delaying the time of crosslinking network structure formation. Alternatively, uniform spherical latex particles were prepared by bringing forward the particle coagulation time using cationic initiator, 2, 2′-azobis (2-methylpropionamidine) dihydrochloride (AAPH). This study presents a new idea that would further broaden the application of particle coagulation in emulsion polymerization.     

丙烯酸酯共聚物乳液自交联反应的研究

本文研究了含环氧基的丙烯酸酯四元共聚物乳液交联后的溶胀度、自交联反应及动力学.结果表明:交联共聚物的溶胀度Q随甲基丙烯酸环氧丙酯单体含量的增加而降低,共聚物在受热的情况下,环氧基因在羧基的作用下开环而发生交联反应,产生网状结构.     

Evidence for a new metastable crystalline phase of strontium nitrate

The undercooling of aqueous solutions of strontium nitrate a few mm³ in volume or microsized by dispersion within an emulsion is investigated. The experimental results are consistent with a succession of transformations in undercooled solutions of binaries. Following concentration, the undercoolings are from 14°C to 20°C for macrosamples or from 39°C to 60°C with emulsions. However it is observed that Sr(NO₃)₂ crystallizes into a metastable phase which can be preserved for a long time. The existence of this metastable crystalline phase has been evidenced by Differential Scanning Calorimetry and by an original evaporation method. The phase diagram, including the metastable phase, is presented.     

Physicochemical characterization of black seed oil-milk emulsions through ultrasonication

The ultrasonic formation of stable emulsions of a bioactive material, black seed oil, in skim milk was investigated. The incorporation of 7% of black seed oil in pasteurised homogenized skim milk (PHSM) using 20 kHz high intensity ultrasound was successfully achieved. The effect of sonication time and acoustic power on the emulsion stability was studied. A minimum process time of 8 min at an applied acoustic power of 100 W was sufficient to produce emulsion droplets stable for at least 8 days upon storage at 4 ± 2 °C, which was confirmed through creaming stability, particle size, rheology and color analysis. Partially denatured whey proteins may provide stability to the emulsion droplets and in addition to the cavitation effects of ultrasound are responsible for the production of smaller sized emulsion droplets.     

Evidence of self-affine multiplicity fluctuation of target residues in ^84Kr-AgBr interactions at 1.7 AGeV

Self-affine multiplicity scaling is investigated in the framework of a two-dimensional factorial moment methodology using the concept of the Hurst exponent （H）. Analyzing the experimental data of target evaporated fragments emitted in ^84Kr-AgBr interactions at 1.7 AGeV revealed that the best power law behavior is exhibited for H = 0.3 indicating a self-arlene multiplicity fluctuation pattern. A signal of multifractality is also observed from knowledge of the anomalous fractal dimension dq extracted from the intermittency exponent aq of the anisotropic phase space scenario.