New hyperbranched hydrophobic cross‐linkers with peripheral azide groups were synthesized as follows: First, star‐shaped polycaprolactones (sPCL) were synthesized by ring‐opening polymerization of caprolactone in the presence of pentaerythritol and tin (II) octoate. In the next step, sequential acrylation, Micheal addition, tosylation, and azidation by acryloyl chloride, diethanol amine, tosyl chloride, and sodium azide were respectively exploited to synthesize azide‐functionalized hyperbranched star‐shaped polycaprolactones which were named sPCL‐acrylate‐diethanolamine‐azide (sPCL‐AC‐DEA‐N3) and sPCL‐acrylate‐diethanolamine‐acrylate‐diethanolamine‐azide (sPCL‐AC‐DEA‐AC‐N3). All steps were thoroughly characterized by FT‐IR and 1H NMR spectroscopy. The GPC analysis showed that the molecular weight of sPCL increased after two azide functionalizations. Amphiphilic hydrogels based on sPCL‐AC‐DEA‐N3 (Mn = 8130 g/mol) and sPCL‐AC‐DEA‐AC‐N3 (Mn = 10112 g/mol) with linear alkyne‐terminated polyethylene glycols (PEG) (Mn = 2000, 4000, and 6000 g/mol) were synthesized through click coupling between azide and alkyne groups. In both hydrogels, the swelling ratio increased by increasing the molecular weight of PEG. The obtained results showed that the branching of the cross‐linker, significantly affected the swelling ratio of hydrogels. For instance, the swelling ratio of sPCL‐AC‐DEA‐AC‐N3 and PEG‐6000 (Q = 900) was higher than sPCL‐AC‐DEA‐N3 and PEG‐6000 (Q = 600). Despite the high cross‐linking density of sPCL‐AC‐DEA‐AC‐DEA‐N3–based hydrogels, the amount of released theophylline was higher than sPCL‐AC‐DEA‐N3–based hydrogels, due to the high content of PEG in these hydrogels.
Owing to their high permeability, metallic soft magnetic materials exhibit high potential as microwave absorbers. The great challenge in designing desirable absorption properties from these materials is their large electrical permittivity at microwave frequencies. So, decreasing their permittivity within acceptable limits while keeping permeability at sufficiently high or improved levels is considered an important requirement for matching impedance and obtaining excellent electromagnetic (EM) absorption properties. In the present research, FeCo alloy particles produced employing by a simple wet chemical reduction process with the intention of investigating dependence of their EM properties on synthesis parameters. The characterizations were done with the help of x-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The intrinsic EM properties (ε r , μ r ) in a frequency range of 2-18 GHz were measured by a vector network analyzer (VNA) for the paraffin composites containing obtained products. The results indicated that the concentration of NaOH and metallic salts as the synthesis precursors can tune the permittivity and permeability. Under optimum conditions, bandwidths of 7.3 and 5.5 GHz with thicknesses of only 1.2 and 1.5 mm were obtained respectively. Also, Reflection loss (RL) of −45 dB was attained. The excellent EM absorption properties demonstrated that the synthesized FeCo alloy may be an ideal absorber having both a wide absorption bandwidth and a low thickness.
One-step mechanochemical processing is one of the most useful and effective methods to produce nanoparticles. Prepared materials by this method show novel properties. In this work, Mg-substituted Zn ferrite (Mg x Zn 1−x Fe 2 O 4 ; x = 0.0, 0.2, 0.4, 0.6) nanoparticles were prepared by one-step mechanochemical processing for the first time. In addition, bulk samples with the same compositions were prepared by conventional ceramic method, which served as reference samples. The samples were characterized by the X-ray diffraction and field emission electron microscopy. By a comparison between I (220)/I (222) intensity ratios in X-ray diffraction patterns of the samples prepared by one-step mechanochemical processing and those of the bulk samples, changes in the cation distribution of the samples prepared by one-step mechanochemical processing were followed. Lattice parameters and magnetic properties of the all samples were measured, and their behaviors were discussed.
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