Interconnected Globules Research Articles

Morphological, microstructural and magnetic characteristics of electrodeposited Ni-Fe-W-Cu alloy powders

Nanostructured Ni-Fe-W-Cu alloy powders were electrodeposited from an alkaline ammonium citrate solution on a titanium cathode. Powder particles were dendrite- and cauliflower-shaped. The dendritic particles had a high density of branches made up of interconnected globules. XRD analysis showed that the powder contained an amorphous matrix and FCC nanocrystals of the solid solution of Fe, W and Cu in Ni. As the deposition current density increased, the mean nanocrystal size decreased, and the mean value of internal microstrain and the total weight percent of Fe and Ni in the alloy increased. The powders deposited at higher current densities exhibited higher magnetization. During annealing at temperatures up to 460?C, the powders underwent short-range ordering, which caused an increase in magnetization, whereas at temperatures above 460?C, the magnetization decreased due to the formation of large FCC crystalline grains.

Effect of deposition current density and annealing temperature on the microstructure and magnetic properties of nanostructured Ni-Fe-W-Cu alloys

Ni-Fe-W-Cu alloy powders were obtained by electrodeposition from an ammonium citrate bath at current densities ranging between 70 and 600 mA cm-2. As the deposition current density increased, the contents of Fe and W in the alloy increased, and those of Ni and Cu decreased. The total cathodic polarization curve was recorded, and partial polarization curves for Ni, Fe and W deposition and hydrogen evolution were determined. The current efficiency of alloy deposition was measured. The powders contained an amorphous matrix and FCC nanocrystals of the solid solution of Fe, W and Cu in Ni. At high current densities, small-sized nanocrystals exhibiting high internal microstrain values were formed. Powder particles were dendrite- and cauliflower-shaped. The dendrites had a large number of secondary branches and higher-order branches containing interconnected globules. The density of branches was higher in particles formed at high current densities. The powders formed at high current densities exhibited higher magnetization. Annealing at temperatures up to 460?C resulted in structural relaxation, accompanied by an increase in magnetization. At temperatures above 460?C, amorphous matrix crystallization and FCC crystal growth took place, accompanied by a decrease in magnetization.

C10H8N2-PPy hybrid flexible electrodes: SILAR synthesis and electrochemical study

2,2′-bipyridine has been significantly focused by researchers because of its electrical conductivity, chelating properties and ability to affect the color and electrochemical properties of the materials. In present work, 2,2′-bipyridine:polypyrrole (C10H8N2:PPy) hybrid flexible electrodes (HFE) have been fabricated by successive ionic layer adsorption and reaction technique using 0.1 M solution of pyrrole (Py) acidified with 0.1 M HClO4 and 30 wt% H2O2 at 366.15 K. XRD pattern of the HFE exhibits characteristic broad peak at 2θ angles 22.35° and 23.09° as well as at 27ο are indicating the formation of bipyridine as well as PPy respectively. The characteristic peak at 1559 cm−1 in the FTIR spectrum is due to pyrrole ring vibrations confirms the formation of PPy. The SEM image of HFE with 30 s dipping time each in pyrrole and H2O2, depicts flesh like morphology with interconnected globules. The contact angle ~ 10° indicate hydrophilic nature of HFE. Cyclic voltammetric (CV) analysis and galvanostatic charge discharge (GCD) have been carried out in 0.5 M H2SO4. The CV curves represent the symmetric and reversible nature at lower scan rate which becomes quasi irreversible and asymmetric at higher scan rates. The observed maximum specific capacitance was 281.49 F/g at 5 mV/s which is nearly same as given by GCD which was 209 F/g at 1 mA/cm2. These HFE are useful for high energy supercapacitors and battery applications.

Monitoring the morphology development of polymer-monolithic stationary phases by thermal analysis

Thermal analysis and SEM were employed to gain insights in the different stages of morphology development and the thermal properties of polymer-monolithic stationary phases. The studied system was a thermally initiated free-radical copolymerization reaction at 70°C of styrene and divinylbenzene in the presence of tetrahydrofuran and 1-decanol. The key events in the early stages of morphology development are initiation, chain growth, branching, and cyclization, leading to microgel particles. Interparticle reactions through pendant vinyl groups lead to the formation of microgel clusters. The rapid increase in molecular weight and cross-link density of the microgel clusters causes a reaction-induced phase separation, and the formation of a macroscopic network of interconnected globules was observed (macrogelation) at around 45 min. After 3 h or 65% conversion, a space-filling macroporous monolithic network was observed. Afterwards, mainly growth of existing globules takes place, reducing the macropore size. The porogen ratio affects the timing of the reaction-induced phase separation, strongly influencing the morphology of the polymer material. The use of a mixture of divinylbenzene isomers yielded a monolithic material that is less cross-linked at the surface compared to the central part of the polymer backbone due to copolymerization-composition drift. The less cross-linked outer layer starts devitrifying at 100°C.

Effects of additives on dual-layer hydrophobic–hydrophilic PVDF hollow fiber membranes for membrane distillation and continuous performance

The advantages of the implementation of dual-layer hydrophobic–hydrophilic hollow fiber membranes for membrane distillation (MD) have been highlighted in this work. The effects of incorporating methanol as a non-solvent additive and self-synthesized fluorinated silica (FSi) particles as a hydrophobic modifier on the resultant membrane morphology and MD performance were investigated. Employing a 3.5wt% sodium chloride solution at 80°C, the highest direct contact membrane distillation (DCMD) flux of 83.40±3.66kg/(m2h) and separation factor higher than 99.99% were attained for the membrane spun with methanol additive. Moreover, the stability of the dual-layer hydrophobic–hydrophilic hollow fiber membrane has been demonstrated through continuous DCMD experiments for 5 days. The separation factor was maintained higher than 99.99% for the membrane spun with methanol additive, verifying the suitability of the dual-layer hydrophobic–hydrophilic hollow fiber membrane configuration for desalination processes. The morphological transformation of the outer membrane surface from a porous agglomerated globule structure into a denser interconnected globule structure may be accounted for by the stability improvement of the membrane spun with methanol additive. On the other hand, it was found that an enhanced hydrophobicity of the membrane spun with FSi particles did not result in an improvement of the membrane stability. The existence of the hydrophilic hydroxyl group on the FSi particle surface may favor the occurrence of membrane wetting.

Low-profile mechanisms in a PVAc/polyester blend

The different steps associated with the curing of a PVAc/polyester blend are identified and correlated to the mechanism of shrinkage control in the presence of a low-profile additive (LPA). Poly(vinyl acetate) (PVAc) is used as a LPA and is shown to induce a phase separation upon curing that leads to an interconnected globule morphology. This morphology strongly modifies the rheokinetics of the blend compared to that of the neat polyester resin. In particular, the presence of PVAc delays the cure kinetics and the gel time. A comparison between these delays, called shift times, demonstrates an increase in the gel conversion of polyester in the presence of PVAc. This, coupled to the thermal expansion of PVAc at the early stages of curing, contributes to the low-profile effect. Microvoids in the LPA-rich phase, which are believed to play a key role in the mechanism of shrinkage control, are efficient at the later stages of curing and during cooling and complete the low-profile effect. However, it is also shown that the formation of microvoids may indirectly induce macroscopic voids that could be at the origin of pinholes at the surface of the parts molded with this material.

Studies on the Phase Separation of Poly(ether imide)-Modified Epoxy Resin, 5. Phase Separation Behavior of a Quasi-Binary System

In this work we present a quasi-binary system for the study of reaction-induced phase separation. Differential scanning calorimetry (DSC) shows that the reaction mechanism of epoxy resin cured by C11Z-CNS imidazole is simple without being affected by the addiction of poly(ether imide) (PEI). The phase structure of interconnected globules was observed by scanning electron microscopy (SEM), and the phase separation is driven by spinodal decomposition as introduced by synchrotron radiation small-angle X-ray scattering (SR-SAXS).

Structure development in epoxy resin modified with poly(ether sulphone)

Structure development during the curing reaction in a ternary mixture of diglycidyl ether of bisphenol A (epoxy), poly(ether sulphone) (PES) and diaminodiphenylmethane (curing agent) was investigated by light scattering, scanning electron microscopy (SEM) and differential scanning calorimetry. In the early stage of curing, the ternary blend was a single-phase mixture. As the cure reaction proceeded, phase separation took place via the spinodal decomposition induced by the increase in the molecular weight of epoxy. This was supported by the characteristic change in light-scattering profile with curing time. SEM observation revealed the formation of a unique two-phase structure: connected globules of epoxy-rich phase arranged regularly (typical periodic distance, 0.5 μm) in a matrix of a PES-rich phase. The unique structure is assumed to be formed under a specific situation: competitive progress of phase separation and of the crosslink reaction. That is, once a loose network is established at the epoxy-rich region in the phase-separated system, further coarsening to a droplet-type structure could be suppressed, eventually resulting in the interconnected globule structure. Compared with neat epoxy resin, the cured ternary resin exhibited higher adhesive strength, in both peel and shear modes. The excellent adhesive property seems to originate from the characteristic connected-globule morphology.

Resinite: its infrared spectrum and coalification pattern

On the basis of infrared spectral studies some years ago, it was suggested that the maceral resinite was comprised of two contrasting chemical-structural groups: one confined to peats, brown coals, lignites and sub-bituminous coals, the other to the low- and mediumrank bituminous coals. There was little evidence of the existence of resinites with transitional spectra. The maceral frequently occurred in bituminous coals as veins or interconnected globules probably formed by migration at sub-bituminous levels of coalification. Further support came from their differing responses when carbonized: the highly aliphatic resinites from low-rank deposits distilled with little polymerization or increase in aromaticity, but those from bituminous coals appeared to eliminate non-aromatic CH with development of increasing aromaticity. Recent petrological studies in independent laboratories confirm the contrast between the groups, and the migration, but also suggest that much resinite in bituminous coals is of secondary origin and is due to expulsion from several macerals during the sub-bituminous rank stage, the coalification level corresponding to the period of maximum petroleum generation from crustal organic matter.