Microscale Porous Structure Research Articles

Bubble-Guidance Breaking Gas Shield for Highly Efficient Overall Water Splitting.

Overall water splitting is a promising technology for sustainable hydrogen production, but the primary challenge is removing bubbles from the electrode surface quickly to increase hydrogen production. Inspired by the directional fluid transport properties of natural biological surfaces like Nepenthes peristome and Morpho butterfly's wings, here a strategy is demonstrated to achieve highly efficient overall water splitting by a bubble-guidance electrode, that is, an anisotropic groove-micro/nanostructured porous electrode (GMPE). Gradient groove micro/nanostructures on the GMPE serve as high-speed bubble transmission channels and exhibit superior bubble-guidance capabilities. The synergistic effect of the asymmetric Laplace pressure generated between microscale porous structure and groove patterns and the buoyancy along the groove patterns pushes the produced bubbles directionally to spread, transport, and detach from the electrode surface in time. Moreover, the low adhesive nanosheet arrays are beneficial to reduce bubble size and increase bubble release frequency, which cooperatively improve mass transfer with the microscale structure. Notably, GMPE outperforms planar-micro/nanostructured porous electrode (PMPE) in hydrogen/oxygen evolution reactions, with GMPE||GMPE showing better water splitting performance than commercially available RuO2||20 wt.% Pt/C. This work improves electrodes for better mass transfer and kinetics in electrochemical reactions at solid-liquid-gas interfaces, offering insight for designing and preparing gas-involved photoelectrochemical electrodes.

Enhanced interfacial bonding strength of hot-pressed titanium Alloy/CFRTP joint via laser ablation and interfacial adhesive

Joining titanium alloy with carbon fiber reinforced thermoplastic (CFRTP) is one of the hot subjects in the automotive and aerospace industries. To improve the joint strength of TC4/CFRTP PA6, this study combined the surface treatment of TC4 alloy, including laser ablation, Silane Coupling Agent (SCA) treatment, and interfacial PA6 adhesive. The results showed that the pretreatment and the laser texturing induced the micro-scale porous and macro-scale groove grid structure, respectively. The superhydrophilicity of the laser texturing as well as amino polar groups induced by SCA treatment promoted the adhesion of the thermoplastic PA6 melt into the microstructure of the TC4 alloy surface. The mechanical interlocking and hydrogen bonding between TC4 alloy and CFRTP PA6 significantly improved the shear strength of the TC4/CFRTP PA6 joint (17.5 MPa). Furthermore, with the incorporation of interfacial PA6 adhesive, the joint strength was further enhanced, and the damage of the TC4/CFRTP PA6 joint was transformed from interfacial to interlaminar CFRTP PA6.

An Approach for Fabricating Hierarchically Porous Cell‐Laden Constructs Utilizing a Highly Porous Collagen‐Bioink

AbstractIn bioprinting procedures, bioinks typically comprise hydrogels, necessitating a balance between printability and bioactivity. Achieving good printability requires a relatively high hydrogel viscosity, but this can reduce bioactivity due to poor cell‐to‐cell interactions of the encapsulated cells. Therefore, developing hydrogels with excellent printability and bioactivity is a significant challenge in bioprinting. Here, a collagen‐based bioink with excellent printability and bioactivity is developed. The bioink is prepared through a two‐step process: first, by subjecting the bioink to whipping to create a non‐homogeneous porous structure, and subsequently, by employing centrifugation to refine this porous structure into a uniform and relatively smaller microscale porous structure (with a specific diameter of 15.7 ± 9.2 µm). Using the designed bioink, a hierarchical porous structure is fabricated without any special equipment or supporting/sacrificing materials. To demonstrate the feasibility of the collagen bioink laden with human adipose stem cells, a hierarchical cell construct is fabricated using a bioprinter. The construct exhibits significantly enhanced cellular activities and superior osteogenic differentiation compared to the bioprinted cell constructs using normal collagen bioink. These findings suggest that collagen‐based bioinks, which are both printable and bioactive, hold significant promise for extensive utilization in a variety of tissue regeneration applications.

Block Sequence Effects on the Self-Assembly Behaviors of Polypeptide-Based Penta-Block Copolymer Hydrogels.

Peptide-based hydrogels have great potential for applications in tissue engineering, drug delivery, and so on. We systematically synthesize, characterize, and investigate the self-assembly behaviors of a series of polypeptide-based penta-block copolymers by varying block sequences and lengths. The copolymers contain hydrophobic blocks of poly(γ-benzyl-l-glutamate) (PBG, Bx) and two kinds of hydrophilic blocks, poly(l-lysine) (PLL, Ky) and poly(ethylene glycol) (PEG, EG34), where x and y are the number of repeating units of each block, where PBG and PLL blocks have unique functions for nerve regeneration and cell adhesion. It shows that a sufficient length of the middle hydrophilic segment capped with hydrophobic end PBG blocks is required. They first self-assemble into flower-like micelles and sequentially form transparent hydrogels (as low as 2.3 wt %) with increased polymer concentration. The hydrogels contain a microscale porous structure, a desired property for tissue engineering to facilitate the access of nutrient flow for cell growth and drug delivery systems with high efficiency of drug storage. We hypothesize that the structure of Bx-Ky-EG34-Ky-Bx agglomerates is beyond micron size (transparent), while that of Ky-Bx-EG34-Bx-Ky is on the submicron scale (opaque). We establish a working strategy to synthesize a polypeptide-based block copolymer with a wide window of sol-gel transition. The study offers insight into rational polypeptide hydrogel design with specific morphology, exploring the novel materials as potential candidates for neural tissue engineering.

Design of Hierarchical Porosity Via Manipulating Chemical and Microstructural Complexities in High-Entropy Alloys for Efficient Water Electrolysis.

Achieving a porous architecture with multiple‐length scales and utilizing the synergetic effects of multicomponent chemicals bring up new opportunities for further improving the electrocatalytic performance of nanocatalysts. Herein, the synthesis of a self‐supported hierarchical porous electrocatalyst based on a high‐entropy alloy (HEA) containing multiple transitional metals via physical metallurgy and dealloying strategies is reported. Microscale phase separation and nanoscale spinodal decomposition are modulated in a highly concentrated FeCoNiCu HEA, which makes it possible to obtain a porous structure with different length scales, i.e., relatively large porous channels formed by removing one separated phase and ultrafine mesopores obtained from leaching out one decomposition phase. The resultant hierarchical porous HEA exhibits superior water splitting performance, which takes full advantage of the enlarged surface area offered by the bi‐continuous mesoporous structure with the exceptional intrinsic reactivity originating from the synergetic electronic effects of the different components in alloying. Moreover, the microscale porous structure plays an important role in the significantly improved mass transportation, as well as the durability during electrocatalysis. This effective strategy that simultaneously utilizes the chemical and microstructural advantages of HEAs opens up a new avenue for developing HEA‐based, high‐performance porous electrocatalysts for various energy conversion/store applications.

A novel hierarchical structure comprised of biomass-derived porous carbon and silicon carbide nanowires for highly efficient microwave absorption

Recently, porous carbon-based composites with nano- or micro-pores have been considered as attractive alternatives for microwave absorption. However, the dispersity and uniformity of nanomaterials in the porous carbon is not desirable, inducing poor interfacial compatibility and impedance mismatch. Herein, a novel biomass-derived hierarchically porous C/SiC composite (HPCC) with a two-level structure was successfully fabricated. The first level of microscale porous structure templated from dried apple, while the nanoscale bioinspired structure was constructed by in situ growth of SiC nanowires. The hierarchical structures were conducive to enhancing the microwave absorption performance of HPCC. The reflection loss of HPCC was −44.2 dB at a thickness of 1.5 mm, and the broad effective absorption bandwidth reached 4.2 GHz. The synergistic effects of the hierarchical structure on adjusting the impedance matching and the multiple loss mechanisms were investigated in detail. The results provide valuable guidance for fabricating hierarchical structures with high microwave absorption performance.

Flexible pCu2Se-nAg2Se thermoelectric devices via in situ conversion from printed Cu patterns

Flexible thermoelectric (TE) devices have great potential in wearable electronics, but there is great challenge to realize robust TE device with high performance via feasible integration process. Herein, based on precisely printed copper patterns, a flexible pCu2Se-nAg2Se TE device is initially realized by in situ ion exchange reaction. The as-prepared Cu2Se and Ag2Se films possess typical hierarchical defects including atomic scale vacancies, the nanosheet fragments and microscale porous structure, which could significantly scatter phonons in wide frequency range. Accordingly, ultra-low thermal conductivity (Cu2Se: 0.13 W m−1 K−1; Ag2Se: 0.15 W m−1 K−1) and optimal ZTs (Cu2Se: 0.5; Ag2Se: 0.7) are achieved. Meanwhile, the as-fabricated pCu2Se-nAg2Se TE device exhibits an excellent power density of 13.4 W m−2 at a temperature gradient of 40 K, which is among the highest values of printed in-plane film devices. Furthermore, the good adhesion between TE films and porous PI substrate endowed excellent flexibility and stability of pCu2Se-nAg2Se devices.

Directly Printed Low-Cost Nanoparticle Sensor for Vibration Measurement during Milling Process.

A real-time, accurate, and reliable process monitoring is a basic and crucial enabler of intelligent manufacturing operation and digital twin applications. In this study, we represent a novel vibration measurement method for workpiece during the milling process using a low-cost nanoparticle vibration sensor. We directly printed the vibration sensor based on silver nanoparticles positioned onto a polyimide substrate using an aerodynamically-focused nanomaterials printing system, which is a direct printing technique for inorganic nanomaterials positioned onto a flexible substrate. Since it does not require any post-process such as chemical etching and heat treatment, a highly sensitive vibration sensor composed of a microscale porous structure was fabricated at a cost of several cents each. Furthermore, accurate and reliable vibration data was obtained by simple and direct attachment to a workpiece. In this study, we discussed the performance of vibration measurement of a fabricated sensor in comparison to a commercial vibration sensor. Using frequency and power spectrum analysis of obtained data, we directly measured the vibration of workpiece during the milling process, according to a process parameter. Lastly, we applied a fabricated sensor for the digital twins of turbine blade manufacturing in which vibration greatly affects the quality of the product to predict the process defects in real-time.

Flow of quasi-spherical nanoparticles in liquid composite molding processes. Part I: Influence of particle size and fiber distance distribution

This paper studies the flow and filtration of two quasi-spherical NPs (silica and boehmite) during liquid composite molding (LCM) processes. The nanosuspensions are prepared differently by “top-down” and “bottom-up” approaches, and the particle size is analyzed before and after injection process. In parallel, the fiber distance distribution is systematically characterized using improved image processing techniques and algorithms. It is found that nanosuspensions that are prepared by “top-down” approach may show a bimodal particle distribution, and that the filtration of quasi-spherical NPs is closely related to the bimodal distribution characteristics of the particle size and the dual-scale characteristic of the preform. Furthermore, a threshold fiber volume fraction (Vf) of 55% is identified, at which the investigated preform shows a critical phase transition from dual-scale to single micro-scale porous structure. It is shown that above the threshold Vf even a small fraction of coarse particles can strongly hinder the impregnation process.

3D-printed PCL/bioglass (BGS-7) composite scaffolds with high toughness and cell-responses for bone tissue regeneration

CaO-SiO2-P2O5-B2O3 bioglass (BGS-7) showed highly bioactive properties including osteoconductivity and good mechanical strength, but it has extremely brittle property. In this study, we developed a composite scaffold, which is incorporated into poly(ε-caprolactone)(PCL), to overcome the mechanical disadvantage of the bioglass scaffold. The composite scaffolds were fabricated with a microscale porous mesh structure using a 3D melt-printing process. Surface topographical images demonstrated that the bioglass particles were distributed homogeneously throughout the composite scaffolds. The mechanical properties (compression and three-point bending test) of the composite scaffolds showed the toughness of the composite scaffolds was significantly improved compared to that of the pure bioglass scaffold with a similar porosity. We characterized the in vitro biological properties of the pure PCL, BGS-7, and composite scaffolds using MC3T3-E1 cells. As the weight fraction of bioglass increased, the cell proliferation and osteogenic activities significantly increased owing to the enhanced hydrophilic property, protein absorption, and precipitation of calcium phosphate from the bioglass. However, for the high weight fraction of bioglass (60wt%) in the composite scaffold, the toughness was significantly lower than that of the composite scaffold (40wt%). Based on these results, the appropriate concentration (40%) of the BGS-7 in the composite showed meaningful bioactivities and toughness.

Anode Design Based on Microscale Porous Scaffolds for Advanced Lithium Ion Batteries

Considering the increasing demands for advanced power sources, present-day lithium-ion batteries (LIBs) must provide a higher energy and power density and better cycling stability than conventional LIBs. This study suggests a promising electrode design solution to this problem using Cu, Co, and Ti scaffolds with a microscale porous structure synthesized via freeze-casting. Co3O4 and TiO2 layers are uniformly formed on the Co and Ti scaffolds, respectively, through a simple thermal heat-treatment process, and a SnO2 layer is formed on the Cu scaffold through electroless plating and thermal oxidation. This paper characterizes and evaluates the physical and electrochemical properties of the proposed electrodes using scanning electron microscopy, four-point probe and coin-cell tests to confirm the feasibility of their potential use in LIBs.

Multi-Scale Modeling of Transports inside PEMFC By Combining Multi-Phase CFD Fuel Cell Model with Lattice Boltzmann Method

The objective of this work is to gain the mechanical understanding of the water management in the proton exchange membrane fuel cell (PEMFC). Water is a by-product of the fuel cell reaction and its amount is proportion to the current of fuel cell output. Water is used to retain the proper hydration level in the PEM. At the same time, condensed water in the flowfield and the gas diffusion layer (GDL) reduces oxygen transport to the oxygen reduction reaction (ORR) area. Therefore, excess accumulation of condensed water causes to lower the performance, particularly at the higher current densities. Detailed simulation of two-phase water in the GDL is significantly important to understand the water management.This work shows the successful in development of a multi-scale calculation technique that incorporates various scales of numerical model in a fuel cell and simultaneously performed a prediction. The outcomes of this work are, (i) development of two-phase fluid model in the micro-scale porous structure of GDL, and (ii) integration of this micro-scale GDL fluid model with a state-of-the-art macro-scale flowfield fluid model to predict two-phase water in the fuel cell. Figure 1 gives the concept of modeling approach at each component of the fuel cell. The flowfield in the bipolar plate and MEA models are calculated using traditional computational fluid dynamics (CFD) method with existing PEMFC model [1-3]. The two-phase fluid in the micro-scale porous structure of GDL is numerically predicted by Lattice Boltzmann Method (LBM) [4-5]. The solution of each iteration from CFD and LBM are required to simultaneously exchange for the next iteration until all solutions are converged, especially at the interfaces. In this figure, it shows the flowfield is transformed into the macro-scale CFD model and the image of detail structured GDL is converted into micro-scale LBM model. Actual porous structure imaging of GDL is obtained by the nano-scale high special resolution x-ray computed tomography. Figure 2 shows an example of the predictions from the simulation when the macroscopic flowfield model is combined with the microscopic GDL model while performing the calculation. The predictions give the detail distributions of variables in every components of the multiscale model. In this figure, the current density distribution on MEA surface, the liquid water transport inside the GDL, and the temperature of solid and fluid phases inside the GDL are presented.

Thermofluid Characteristics in Microporous Structure With Different Flow Channels for Loop Heat Pipe

The use of two-phase heat transfer devices using capillary action in a microscale porous structure such as a loop heat pipe (LHP) is a promising heat transport technology. This is because they have characteristics of higher heat transfer power and longer heat transport distances with no electrical power compared with conventional heat pipes. The thermal performance of an LHP is governed by the thermofluid behavior in a microscale porous structure called the wick. In this research, high-performance wicks made of polymer have been developed, and their pore distribution and permeability were evaluated. The effects of the vapor channel's shape on the loop's thermal performance have been investigated by calculation and experiment to enhance evaporator performance. A mathematical model of the evaporator considering super heat in the channel, pressure drop across the wick, and two-phase pressure loss on the boundary face between the wick and the evaporator case was newly developed. The experiment was also conducted as a function of the groove shapes. From calculations and test results, it was found that in order to increase the maximum heat transport capability and decrease the operating temperature, the groove should be well distributed.

Facile preparation of superhydrophobic and superoleophilic porous polymer membranes for oil/water separation from a polyarylester polydimethylsiloxane block copolymer

To fabricate superhydrophobic membranes for oil/water separation, a mesh serving as a support is usually required for improving mechanical properties and rendering a micro-scale porous structure. Herein, we develop a simple spraying-coating process for producing superhydrophobic and superoleophilic porous polymer membranes without meshes as supports from a fluorinated polyarylester polydimethylsiloxane block copolymer (PAR-b-PDMS). It is exciting that the surface morphology of the PAR-b-PDMS membranes can be controlled by the copolymer solution concentration. The PAR-b-PDMS membranes are endowed with promising superhydrophobicity and superoleophilicity, displaying excellent oil affinity and low water adhesion behaviors. Significantly, the PAR-b-PDMS membranes exhibit fast and efficient separation for oil/water mixtures with separation efficiency as high as 99 %. And after 50 cycles of oil/water separation, the as-prepared membranes can still maintain stable superhydrophobicity and high separation efficiency, indicating good recyclability and durability. Moreover, the fabrication approach presented here can be easily scaled up for producing polymer membranes on a large scale, which makes it very promising for practical oil/water separation.

Fabrication of superhydrophobic and oleophobic Al surfaces by chemical etching and surface fluorination

Hierarchical Al surfaces were fabricated using three different kinds of alkaline-based chemical etching processes. The surface morphology changes to a needle-like microstructure or to nanoscale flakes on a microscale porous structure depending on the chemical solution used. These surfaces were characterized by field-emission scanning electron microscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, and contact angle measurements. After the hydrophobic treatment, the etched Al surface shows non-wetting properties, exhibiting a static contact angle over 150° and a dynamic contact angle less than 5° for deionized water. Oleophobic properties for diiodomethane and N,N-dimethylformamide are exhibited by all etched Al surfaces.

Fabrication of polystyrene microscale porous substrate and its effects on HL-7702 cells behaviors

A novel polystyrene (PS) substrate with microscale porous structure was facilely fabricated by crystalline-controlled casting method using mixed solvent [N,N-dimethylformamide and ethyl alcohol (v/v)] based on the nonsolvent induced phase separation process. The substrate surfaces exhibited a bi-continuous microscale porous morphology with high porosity, large pore size and pore-pore connection structure. Moreover, behaviors of the normal human liver cell line (HL-7702) seeded on this substrate surface were carefully investigated. The results indicated that the cell adhesion, spread and cell-cell connection on the surface with subcellular pore size (∼ 10 μm) were similar to the cells proliferated on the flat PS surface. However, the number of HL-7702 cells proliferated on the PS microscale porous surface was higher than cells on the conventional PS flat surface, suggesting that the pore-pore structure was conducive to HL-7702 cell proliferation. Furthermore, hematoxylin and eosin staining and micronucleus test were performed. The results showed that fewer damages for nuclear and cytoplasm and less cell genotoxicity were caused by the microscale porous structure within the scope of pore size (∼ 10 μm) than that of the flat surface.

The improving electrochromic performance of nickel oxide film using aqueous N,N-dimethylaminoethanol solution

New nickel oxide thin films with a micro-scale thickness and porous structure were fabricated using a sol–gel method in a mixed solvent containing N,N-dimethylaminoethanol (dmaeH) and distilled water at a 1:1 ratio. After annealing, the deposited film transformed to a well oriented, porous nickel oxide thin film. This nickel oxide thin film showed enhanced charge capacity and greater optical transmittance changes in a lithium-based electrolyte, and may be applied to WO3/Li+-based electrolyte/NiO electrochromic devices requiring long cycles.

107 ナノ・ミクロ多重多孔質層による伝熱促進に関する共同研究(FM-1 技術移転を目指す熱・燃焼工学最前線,研究発表講演)

Heat transfer enhancement is one of key issues of saving energies and compact designs for mechanical and chemical devices and plants. We discover a high convective heat transfer performance compared to the well-known heat transfer correlations caused by nano- and micro-scale structure formed on the heat transfer surface: the maximum increase of heat transfer coefficient was around 80%. Moreover, we have done some experiments using a co-current flow heat exchanger. We also obtained high performance compared to the usual correlation. In order to form nano- and micro-scale structure on surfaces, we have developed three treatment methods of Nano-particle Porous Layer method (NPL method), Fine Precipitates method (FP method) and Nano- and Micro-scale Porous Layered Structure method (NMPLS method). We guess by the molecular dynamics simulations that the mechanism of heat transfer enhancement by nano- and micro-scale structure on surface might be an artificial property change in the vicinity of the interface by complex structures of particles and porous from nanometer to sub micrometer scales.