Impact of impeller type on methyl methacrylate emulsion polymerization in a batch reactor

The emulsion polymerization of methyl methacrylate (MMA) was carried out in a lab‐scale reactor, which was equipped with a top‐entry agitator, four wall baffles, a U‐shaped cooling coil, and a temperature controller. Potassium per sulfate and sodium dodecyl sulfate as were used as the initiator and the surfactant, respectively. The experimental investigation demonstrated the impact of the impeller type (45° six pitched‐blade turbine and Rushton impeller), number of impellers (single and double impellers), and impeller speed (100–350 rpm) on the monomer conversion, polymer particles size, molecular weight, and glass transition temperature. The results revealed that the effect of the impeller speed on the characteristics of the polymer attained using the pitched‐blade turbine was more prominent than that for the Rushton turbine. It was also found that the impact of the impeller speed on the polymer characteristics was much more pronounced for the double pitched‐blade turbines rather than for the double Rushton turbines. However, more uniform size distribution was achieved with the Rushton turbine. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40496.     

Application of the nondestructive second derivative spectrophotometry to eliminate the effect of substrate in identification of madder used in Persian carpets

The handmade Persian carpet is famous worldwide not only for its elegant design and artistic structure, but also for its brilliant color harmony and incomparable raw materials. Various natural dyes accompanied by different mordants are used on various woolen yarns to obtain a wide range of unrepeatable shades for carpet. In this article, as a first step, the diversity of the undyed woolen yarns used in Persian carpets was statistically investigated by implementation of the Principle Component Analysis. Then the second derivative of Kubelka‐Munk function of samples dyed with madder was considered to reach a pattern for identifying madder. The results show that, although the spectral reflectance of different selected woolen yarns has at least 3 dimensions, all derivative curves are qualitatively very similar with the same minimum and maximum peaks at 510 and 605 nm, respectively. The findings are confirmed when various types of madder were used in the dyeing process. As a result, it is shown that the nondestructive derivative spectrophotometry is able to identify madder on alum mordanted woolen yarns used in Persian carpets and to eliminate the effect of substrate. It is a useful technique for preservation, conservation, and dissemination of the Persian carpet.     

Effect of processing conditions on the microencapsulation of 1-methylimidazole curing agent using solid epoxy resins

Among various methods for preparation of the non-reactive or latent curing agents for epoxy resins, encapsulation offers a promising and cost-effective method. This system has been used in one-part thermosetting adhesives or prepregs for developing advanced composite materials. In this study, 1-methylimidazole (1-MI) was microencapsulated using solid epoxy resins via solvent evaporation method. The effect of various types of shell materials or solid epoxy resins, different core-to-shell ratios of 30/70, 50/50, and 70/30, and a variety of mixing rates (500, 1000, and 1500 rpm) on the preparation of microcapsules were evaluated. The 1-MI content and microencapsulation efficiency were calculated using thermal gravimetric analysis (TGA). The shape and surface morphology of the prepared microcapsules were evaluated using scanning electron microscopy (SEM) technique. Gel time of the microcapsules mixed with liquid epoxy resin was also investigated. Results showed that by decreasing the core-to-shell ratio at different stirring rates, the encapsulation efficiency increased. The microencapsulation efficiency of 34.8% was obtained at shell-to-core (1-MI) ratio of 70/30 at stirring rate of 500 rpm. The results also showed that at higher mixing rates, 1-MI content in microcapsules was controlled by high shearing force. It has been found that the gel time of the epoxy resin/microcapsule samples was proportional to the imidazole content and it was in agreement with the data obtained by TGA analysis, as well.     

Double‐Sided Surface Passivation of 3D Perovskite Film for High‐Efficiency Mixed‐Dimensional Perovskite Solar Cells

Defect‐mediated carrier recombination at the interfaces between perovskite and neighboring charge transport layers limits the efficiency of most state‐of‐the‐art perovskite solar cells. Passivation of interfacial defects is thus essential for attaining cell efficiencies close to the theoretical limit. In this work, a novel double‐sided passivation of 3D perovskite films is demonstrated with thin surface layers of bulky organic cation–based halide compound forming 2D layered perovskite. Highly efficient (22.77%) mixed‐dimensional perovskite devices with a remarkable open‐circuit voltage of 1.2 V are reported for a perovskite film having an optical bandgap of ≈1.6 eV. Using a combination of experimental and numerical analyses, it is shown that the double‐sided surface layers provide effective defect passivation at both the electron and hole transport layer interfaces, suppressing surface recombination on both sides of the active layer. Despite the semi‐insulating nature of the passivation layers, an increase in the fill factor of optimized cells is observed. The efficient carrier extraction is explained by incomplete surface coverage of the 2D perovskite layer, allowing charge transport through localized unpassivated regions, similar to tunnel‐oxide passivation layers used in silicon photovoltaics. Optimization of the defect passivation properties of these films has the potential to further increase cell efficiencies.     

A 3D,Compartmental Tumor-Stromal Microenvironment Model of Patient-Derived Bone Metastasis

Bone is a frequent site of tumor metastasis. The bone–tumor microenvironment is heterogeneous and complex in nature. Such complexity is compounded by relations between metastatic and bone cells influencing their sensitivity/resistance to chemotherapeutics. Standard chemotherapeutics may not show efficacy for every patient, and new therapeutics are slow to emerge, owing to the limitations of existing 2D/3D models. We previously developed a 3D interface model for personalized therapeutic screening, consisting of an electrospun poly lactic acid mesh activated with plasma species and seeded with stromal cells. Tumor cells embedded in an alginate-gelatin hydrogel are overlaid to create a physiologic 3D interface. Here, we applied our 3D model as a migration assay tool to verify the migratory behavior of different patient-derived bone metastasized cells. We assessed the impact of two different chemotherapeutics, Doxorubicin and Cisplatin, on migration of patient cells and their immortalized cell line counterparts. We observed different migratory behaviors and cellular metabolic activities blocked with both Doxorubicin and Cisplatin treatment; however, higher efficiency or lower IC50 was observed with Doxorubicin. Gene expression analysis of MDA-MB231 that migrated through our 3D hybrid model verified epithelial–mesenchymal transition through increased expression of mesenchymal markers involved in the metastasis process. Our findings indicate that we can model tumor migration in vivo, in line with different cell characteristics and it may be a suitable drug screening tool for personalized medicine approaches in metastatic cancer treatment.     

A Method to Distinguish Exchange Coupled Core/Shell Nanostructures from the Mixed One in Synthesized (Fe3O4/CoFe2O4) Nanostructure

Journal of Superconductivity and Novel Magnetism - Two single-phase iron and cobalt ferrite nanoparticles and a bi-magnetic soft/hard nanostructure of Fe3O4/CoFe2O4 were synthesized through the...     

Tomography images to analyze the deformation of the cavern in the continuous‐flow mixing of non‐Newtonian fluids

Tomography, an efficient nonintrusive technique, was employed to visualize the flow in continuous‐flow mixing and to measure the cavern volume (V_c) in batch mixing. This study has demonstrated an efficient method for flow visualization in the continuous‐flow mixing of opaque fluids using two‐dimensional (2‐D) and 3‐D tomograms. The main objective of this study was to explore the effects of four inlet‐outlet configurations, fluid rheology (0.5–1.5% xanthan gum concentration), high‐velocity jet (0.317–1.660 m s^?1), and feed flow rate (5.3 × 10^?5?2.36 × 10^?4 m³ s^?1) on the deformation of the cavern. Dynamic tests were also performed to estimate the fully mixed volume (V_{fully mixed}) for the RT, A310, and 3AM impellers in a continuous‐flow mixing system, and it was found that V_{fully mixed} was greater than V_c. Incorporating the findings of this study into the design criteria will minimize the extent of nonideal flows in the continuous‐flow mixing of complex fluids and eventually improve the quality of end‐products. © 2013 American Institute of Chemical Engineers AIChE J, 60: 315–331, 2014     

Synthesis of Hollow Tadpole-Like Silica Particles

Hollow tadpole-like silica particles were successfully synthesized via the microemulsion synthesis method using polyvinylpyrrolidone (PVP), tetraethyl orthosilicate (TEOS), and sodium citrate as starting materials in the presence of isopropanol as a solvent. The effects of TEOS/ammonia (T/A) ratio, PVP molecular weight, synthesis temperature, and sodium citrate concentration on the morphology of particles were investigated. The results demonstrated that synthesis temperature has a vital effect on the morphology of particles. Also, microstructure analysis showed that the length of the silica rods was tunable in the range 1.2–5.2 µm. Control of the length was obtained by adjusting the synthesis temperature and PVP molecular weight. The transmission electron microscopy results clearly confirmed that the tadpole-like particles were surprisingly hollow and they provided an open side that was completely different from the previous reports. The inner diameter of the silica rods could be adjusted in the range 50–200 nm. The existence of such a considerable open side may be practically appreciated in many potential applications such as bio-immobilization.     

Space‐time block coding in millimeter wave large‐scale MIMO‐NOMA transmission scheme

In this paper, we introduce a new wireless system architecture using space‐time block coding schemes (STBC) and non‐orthogonal multiple access (NOMA) in millimeter wave (mmWave) large‐scale MIMO systems. The proposed STBC mmWave large‐scale MIMO‐NOMA system utilizes two MIMO subarrays, transmitting data over two channel vectors to mobile users. To reduce the communication overhead and latency in the system, we utilize random beamforming with optimal coefficients at the base station and random‐near random‐far user pairing in implementing the NOMA scheme. Our results show that the proposed STBC mmWave large‐scale MIMO‐NOMA technique significantly outperforms the previous counterparts.