Unidirectional Microstructure Research Articles

Unidirectionally Structured Magnetic Phase-Change Composite Based on Carbonized Polyimide/Kevlar Nanofiber Complex Aerogel for Boosting Solar-Thermo-Electric Energy Conversion.

To realize highly efficient solar-thermo-electric energy conversion for clean electricity power generation, we have developed a new type of unidirectionally structured magnetic phase-change composite comprising a carbonized polyimide (C-PI)/Kevlar nanofiber (KNF) complex aerogel as a 3D carbon skeleton porous supporting material, CoFe2O4 nanoparticles as a magnetic additive, polyethylene glycol (PEG) as a phase-change material, and polypyrrole as a photothermal absorption coating layer. The as-fabricated C-PI/KNF complex aerogel exhibits a unidirectional microstructure, high porosity, robust skeleton frame, ultralight weight, and high thermal conductance. Featured with such unique structure and characteristics, the complex aerogel can offer an effective heat and electron transfer method to ensure highly efficient solar-thermal conversion and photothermal energy storage of the developed composite. The developed composite exhibits a high latent heat capacity of over 150 J g-1, outstanding shape stability along with a low leakage of 0.2 wt %, good thermal cycling stability, and high photothermal conversion efficiency of 84.8%. Based on the Seebeck effect, a solar thermoelectric generation system (STEGS) was constructed with the hot side coupled with the developed composite and the cold side immersed in air and ice water. Under 2.0 kW m-2 solar irradiation, the developed STEGS in ice water obtained maximum output voltage and current of 259.7 mV and 27.1 mA, respectively, which are significantly higher than those in air. The output power of the developed STEGS in an ice water environment is 50.6% higher than that in air under 4.0 kW m-2 solar irradiation. More importantly, the developed STEGS in ice water continuously generated output voltage and current for about 810 s without solar irradiation thanks to the latent heat release by the PEG component within the developed composite. In addition, the introduction of magnetic CoFe2O4 can accelerate solar-thermal conversion through periodic electron motion by the Néel relaxation or Brownian relaxation. This resulted in an increase in the maximum output voltage and current by 13.7 and 11.5%, respectively, under an alternating magnetic field as a result of the magnetism-accelerated solar-thermo-electric conversion. This study offers an innovative approach for developing PCM-based advanced functional materials for solar energy utilization in clean and sustainable electricity generation.

Numerical simulation of the effect of unidirectional microstructure on the electrochemical performance of solid oxide fuel cell anode

Numerical simulation of the effect of unidirectional microstructure on the electrochemical performance of solid oxide fuel cell anode

Self-powered aligned porous superhydrophobic sponge for selective and efficient absorption of highly viscous spilled oil

Crude oil spills have caused catastrophic damage to marine ecosystems and become a global challenge. Although various liquid absorption materials have been developed, manual operations such as pumping and electric heating are still required in the face of highly viscous spilled oils. Efficient and autonomous crude oil spill cleanup methods are urgently needed. Here, inspired by the unidirectional microstructure of tree xylem, we report a sponge (SPC-Sponge), which combines superhydrophobic property and aligned porous structures, prepared from a ternary suspension (hydrophobic silica nanoparticles, polyurethane, and cellulose nanofibers) by single-step directional freeze casting. SPC-Sponge not only effectively overcome the limitations of traditional synthetic modification methods on the shape and size of porous sponge materials, but also has excellent oil-water selection function, liquid absorption speed, and liquid absorption capacity compared with common porous materials. Moreover, the sponge can self-absorb highly viscous crude oil of around 80,000 mPa‧s on seawater without external energy and human intervention. By adding multi-walled carbon nanotubes, the sponge can implement in-situ solar heating of crude oil, and the absorption speed is further improved. Given its unique structural design and superwetting property, this SPC-Sponge provides an efficient remediation approach for viscous oil spills.

Effects of lamellar microstructure of retinoic acid loaded-matrixes on physicochemical properties, migration, and neural differentiation of P19 embryonic carcinoma cells

Abstract In this study, retinoic acid loaded-PLGA-gelatin matrixes were prepared with both freeze-casting and freeze-drying techniques. Herein, the effect of unidirectional microstructure with tunable pores on release profile, cellular adhesion, migration, and differentiation was compared. Morphological observation determined that highly interconnected porous structure can be formed, but lamellar pore channels were observed in freeze-casting prepared constructs. The absorption ratio was increased, and the biodegradation rate was decreased as a function of the orientation of microstructure. The in-vitro release study illustrated non-Fickian release mechanism in both methods, so that erosion has predominated over diffusion. Accordingly, PLGA-gelatin scaffolds prepared with freeze-drying technique showed no adequate erosion due to the rigid structure, while freeze-casting one presented more favorable erosion. Microscopic observations of adhered P19 embryonic cells on the scaffolds showed that the freeze-casting matrixes with unidirectional pores provide a more compatible microenvironment for cell attachments and spreading. Besides, it facilitated cell migration and penetration inside the structure and may act as guidance for neuron growth. Improvement in the expression of neural genes in unidirectionally oriented pores proved the decisive role of contact guidance for nerve healing. It seems that the freeze-cast PLGA-gelatin-retinoic acid scaffolds have initial features for nerve tissue regeneration studies.

Fabrication and characterisation of super-paramagnetic responsive PLGA-gelatine-magnetite scaffolds with the unidirectional porous structure: a physicochemical, mechanical, and in vitro evaluation.

Architecture and composition of Scaffolds are influential factors in the regeneration of defects. Herein, synthesised iron oxide (magnetite) nanoparticles (MNPs) by co-precipitation technique were evenly distributed in polylactic-co-glycolic acid (PLGA)-gelatine Scaffolds. Hybrid structures were fabricated by freeze-casting method to the creation of a matrix with tunable pores. The synthesised MNPs were characterised by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy, and vibrating sample magnetometer analysis. Scanning electron microscopy micrographs of porous Scaffolds confirmed the formation of unidirectional microstructure, so that pore size measurement indicated the orientation of pores in the direction of solvent solidification. The addition of MNPs to the PLGA-gelatine Scaffolds had no particular effect on the morphology of the pores, but reduced slightly pore size distribution. The MNPs contained constructs demonstrated increased mechanical strength, but a reduced absorption capacity and biodegradation ratio. Stability of the MNPs and lack of iron release was the point of strength in this investigation and were determined by atomic absorption spectroscopy. The evolution of rat bone marrow mesenchymal stem cells performance on the hybrid structure under a static magnetic field indicated the potential of super-paramagnetic constructs for further pre-clinical and clinical studies in the field of neural regeneration.

Effects of pore orientation on in-vitro properties of retinoic acid-loaded PLGA/gelatin scaffolds for artificial peripheral nerve application

Different manufacturing processes of scaffolds affect their main properties by altering the microstructure of pores. In this study, poly (lactic-co-glycolic acid) (PLGA) scaffolds were synthesized by both freeze casting and freeze drying methods. Scanning electron microscopy (SEM) micrographs demonstrated a unidirectional microstructure in the freeze-cast and a number of random pores in the freeze-dried scaffolds. According to the results, the formation of a lamellar microstructure increased the mechanical strength, swelling ratio, biodegradation behavior and drug release level. Addition of gelatin to the PLGA freeze-cast constructs led to an increase in the average diameter of pores, hydrophilicity and cellular spreading. The gelatin-containing scaffolds showed a decreased mechanical strength, but at the same time, an enhanced swelling ratio, biodegradation rate and drug release level. Differentiation of P19 cells and expression of β-tubulin III, Pax-6 and Nestin were improved by incorporating retinoic acid in PLGA-Gelatin freeze-cast scaffolds. This is a good option with initial necessary features for regenerating peripheral nervous system (PNS).

Physicochemical and mechanical properties of freeze cast hydroxyapatite-gelatin scaffolds with dexamethasone loaded PLGA microspheres for hard tissue engineering applications

Hydroxyapatite (HA)-gelatin scaffolds incorporated with dexamethasone-loaded polylactic-co-glycolic acid (PLGA) microspheres were synthesized by freeze casting technique. Scanning electron microscopy (SEM) micrographs demonstrated a unidirectional microstructure and a decrease in the pore size as a function of temperature gradient. Higher amounts of HA resulted in a decrease in the pore size. According to the results, at lower cooling rates, the formation of a lamellar structure decreased the mechanical strength, but at the same time, enhanced the swelling ratio, biodegradation rate and drug release level. On the other hand, higher weight ratios of HA increased the compressive strength, and reduced the swelling ratio, biodegradation rate and drug release level. The results obtained by furrier transform infrared spectroscopy (FTIR) and bioactivity analysis illustrated that the interactions of the materials support the apatite formation in the simulated body fluid (SBF) solution. Based on the obtained results, the synthesized composite scaffolds have the necessary mechanical and physicochemical features to support the regeneration of defects and to maintain their stability during the neo-tissue formation.

Spinodally decomposed nanostructures in a TiO2–VO2 crystal

We have prepared a single crystal of Ti0.4V 0.6O2 which forms a solid solution crystallizing in the rutile structure at high temperatures and undergoes phase separation due to the spinodal decomposition when cooled to room temperature. The spinodally decomposed crystal consists of a self-assembled, mega stack of alternate Ti- and V-rich layers with an approximate period of 33 nm along the c axis. The unidirectional microstructure causes a large anisotropy in resistivity and a small one in thermal conductivity. A sharp metal–insulator transition as well as a structural transition to a monoclinic structure is observed in the thin V-rich layers.

Effect of Continuous Casting Parameters on Microstructure and Texture of Gold Bonding Wire for Semiconductor Packaging

In this study, we have investigated a texture and microstructure of gold bonding wire by transmission electron microscope, X-ray diffraction and electron back scatter diffraction according to process parameters, such as casting, drawing and annealing processes. The gold was cast into 7mm diameter rods by vertical continuous casting technique, the cast rods were drawn to a final wire size of 25μm, and then the fine wires were annealed. A unidirectional solidification structure having <100> fiber texture of cast rod was strongly developed depending on casting route and speed. In the sample with unidirectional microstructure developed in partial it is found that dislocation substructure with nano-size appeared to display a characteristic feature, while no dislocation substructure is seen in the sample with complete unidirectional microstructure. Interface stability between solid and liquid may be responsible for this difference in dislocation substructure. With decreasing casting speed <100> fiber component became weak. Initial texture plays important role on development of <111> fiber texture at drawing and final annealing stages. On the basis of results obtained it is suggested that both the initial texture are important in controlling the texture of gold bonding wire.

Effects of Initial Texture on Drawing and Recrystallization Characteristics of Gold Bonding Wire

Microstructure and texture formation behavior of a gold rod and fine wire which were produced by continuous casting process and drawing, respectively were investigated by means of optical micrographs, TEM images and X-ray pole figure. Well-developed unidirectional structure aligned to casting direction was found in 7 mm gold rod. Higher casting speed was found to be favor in developing the directional microstructure. In the sample with unidirectional microstructure developed in partial it is found that dislocation substructure with nano-size appeared to display a characteristic feature, while no dislocation substructure is seen in the sample with complete unidirectional microstructure. Interface stability between solid and liquid may be responsible for this difference in dislocation substructure. <100> fiber component was observed to be well developed over the whole microstructure in unidirectional sample. With decreasing casting speed <100> fiber component became weak. Two texture components consisting of <111> fiber and <100> fiber were seen in as-drawn samples. For the development of <111> fiber texture component initial texture component plays a more significant role than subsequent annealing process. Annealing heat treatment would be effective way to control the formation of <100> fiber component. On the basis of results obtained it is suggested that both the initial texture and final annealing are important in controlling the texture of gold bonding wire.

Electrical anisotropic property of some unidirectionally solidified eutectic alloys

The eutectic systems of Cd-Pb, Bi-Cd and Bi-Zn were alloyed using chemically pure raw materials in an electric furnace. The electrical resistivities were determined at room temperature in terms of the microstructures of the eutectic alloys. Electrical resistivities measured parallel and perpendicular to the unidirectional microstructure at different solidification rates were quite distinctive. The electrical resistivities measured were consistent with calculated values. The present study indicates qualitatively that unidirectional solidification of ideal conductor-insulator eutectic systems could produce electrical anisotropic materials.