Wavy Microstructure Research Articles

In-situ CdS nanowires on g-C3N4 nanosheet heterojunction construction in 3D-Optofluidic microreactor for the photocatalytic green hydrogen production

Herein, we reported a simple and cost-effective fabrication method to develop an effective corrugated serpentine OFMR (C-SOFMR) with advanced features, such as expansion/contraction and wavy microstructure. A laminar flow with no back mixing was observed in plain serpentine OFMR (P-SOFMR). While, stretching and folding of fluid along with back mixing was observed in C-SOFMR. Further, the CdS nanowires on g-C3N4 nanosheet (CN/CdS) heterojunction was synthesized in situ both P-SOFMR and C-SOFMR and utilized the device for the photocatalytic green hydrogen generation. The CN/CdS heterojunction endowed with narrow band gap energy (2.01 eV). The longer CdS nanowires (∼110 nm) benefit the electronic interface with CN in the CN/CdS heterojunction and lead to the spatial separation (reduced recombination) of excitons along the CdS axial direction. The charges generated were utilized efficiently for the HER reaction in both P-SOFMR and C-SOFMR at higher flow rates attributing to the rapid micro-mixing and mass transfer. The CN/CdS heterojunction showed the highest photocatalytic activity (6.38 μmol h−1 in C-SOFMR and 6.16 μmol h−1 in P-SOFMR at 1.0 mL min−1) due to its good optronic properties. This study is a path forward for the utilization of advanced optofluidic devices to produce green hydrogen directly from solar energy.

Wavy microstructure for improvement of bonding strength in titanium to carbon steel brazed joints

Multi-interlayer composed of Ni and microcracked Cr (MC-Cr), formed by electrochemical deposition, was applied to induce the formation of wavy microstructure enhancing bonding strength of titanium to carbon steel brazed joints with BAg45CuZn filler. Effect of microcrack density in Cr layer on microstructure evolution and mechanical properties of joints has been studied. Phase identification and formation mechanism of joints were analyzed systematically. Introducing multilayer with microcracks avoided the formation of brittle Ti-C and Fe-Ti phases near carbon steel substrate. During bonding, the diffusion of Ti atoms was hindered by compact Cr while promoted by Ni at microcracks. The inhomogeneous diffusion of Ti atoms led to the generation of a wavy microstructure unit that is crater-shaped structure, accompanied by the enrichment of β-CuZn, Fe0.2Ni4.8Ti5 and Cu2TiZn phases. The fracture results showed that these structures improved the shear strength of joints up to 242 MPa by altering the direction of crack propagation.

Physicochemical structure and functional properties of soluble dietary fibers obtained by different modification methods from Mesona chinensis Benth. residue

Alkaline hydrogen peroxide (AHP), high-temperature cooking combined with ultrasonic (HTCU) and high-temperature cooking combined with complex enzyme hydrolysis (HTCE) were used to modify soluble dietary fiber (SDF) in Mesona chinensis Benth. residue (MCBR), then the structural and in vitro functional properties of A-SDF, HU-SDF and HE-SDF were investigated. Results showed that the three treatments significantly increased the yield of SDF. Scanning electron microscopy, FT-IR, monosaccharide composition, X-ray diffraction, molecular weight distribution and thermal stability analysis were employed to determine the structural changes. Compared with the control SDF (CK-SDF), HE-SDF and HU-SDF had looser and more porous microstructure, as well as lower crystallinity. In contrast to HE-SDF and HU-SDF, A-SDF exhibited a dense wavy microstructure, and elevated crystallinity and thermal stability. In addition, the monosaccharide composition and molecular weight of HU-SDF, HE-SDF and A-SDF were significantly altered as compared to CK-SDF. Moreover, the functional properties of HE-SDF and HU-SDF, including water holding capacity (WHC), oil holding capacity (OHC), glucose adsorption capacity (GAC), α-amylase activity inhibition ratio (α-AAIR), cholesterol adsorption capacity (CAC) and nitrite ion adsorption capacity (NIAC), were significantly higher than those of CK-SDF. However, the dense structure and high crystallinity of A-SDF resulted in a significantly lower GAC and NIAC than that of CK-SDF, with only WHC and α-AAIR being improved. Overall, this study showed that HTCU and HTCE could be used as ideal modification methods for MCBR SDF, HE-SDF and HU-SDF have potential as functional additives in food.

Effects of different tool microstructures on the precision turning of titanium alloy TC21

Titanium alloys are widely used in the aviation field due to the excellent properties, such as high specific-strength and high-temperature resistance. But the poor machinability of titanium alloys has brought the great difficulty to its machining process. In the cutting process of titanium alloys, tool wear is very serious, and the machining quality is difficult to be guaranteed. As a new type titanium alloy, TC21 alloy has the higher strength and its machinability is less than other titanium alloys. Aiming at the cutting defects in the cutting process of TC21 alloy, three different microstructures, including parallel, perpendicular and wavy grooves, are presented and cut on the rake surface of tools by the laser texturing method. A series of precision turning process of TC21 alloy are implemented on the precision machine using the inserts with different microstructures. The effects of the different microstructures on the chip morphology, turning force, surface morphology, and surface roughness are investigated deeply. The results demonstrates that the tool microstructures have very important role on the turning process of titanium alloys and the wavy microstructure has the best effect in improving the machinability of titanium alloy TC21.

Donkey pericardium as a select sourcing to manufacture percutaneous heart valves: Decellularization has not yet demonstrated any clear cut advantage to glutaraldehyde treatment

BackgroundThe donkey pericardium is considered a good candidate to manufacture percutaneous heart valves based upon its thinness, low cellularity and undulating collagen bundles and laminates. Decellularization represents an avenue worth exploring, should its superiority to glutaraldehyde-treated pericardium be demonstrated. Materials and methodsDonkey pericardium was divided into two groups: regular glutaraldehyde fixation and mild decellularization. The treated pericardia were observed using scanning electron microscopy, histology and transmission electron microscopy. Tensile tests were performed along the axial and perpendicular directions, with the data fitted into both the Gasser–Ogden–Holzapfel (GOH) material model and the Fung’s anisotropic one. ResultsThe microstructures of the pericardia processed by the two protocols were similar, showing collagen bundles and laminates free of flaws. The decellularization eliminated most of the cells, however leaving the structure somehow compressed. The collagen filaments in bundles were slightly blurry. The anisotropy rates of the non-decellularized specimens were almost identical to the decellularized ones. The decellularized pericardium appeared stiffer. ConclusionThe decellularization proved to be effective. However, it makes the tissue stiffer, which may lead to higher shear concentration during cardiac cycles and reduce its wavy microstructure. Therefore, it appears premature to select decellularized donkey pericardium to manufacture heart valves.

Impact of surface condition and roughness on sediment formation: an experimental sewer system operated with real wastewater.

Regular sewer cleaning in North Rhine-Westphalia (Germany) generates annual costs of around 50 million Euros. This leads to the question of whether and to what extent sewer cleaning is necessary. To determine the effect of roughness, sewer surface condition and discharge, experiments with real wastewater were performed, using a sewer test track with acrylic glass tubes (DN 300) prepared with abrasive paper and nature stone tiles at the wastewater treatment plant (WWTP) Bochum-Ölbachtal (Ruhrverband, Germany). A logarithmic relationship between deposit height and time was found to lead to maximum deposit heights of 5 to 60 mm. Surface structure analysis by texture measuring indicated that deposits within the first 28 days after cleaning are highly influenced by the surface condition of the sewer and not necessarily by roughness. Furthermore, under dry weather conditions deposit heights are nearly stable after this time, indicating the limiting effect of sewer cleaning. Deposit formation amounted to 1.75-1.80 mm/d at a roughness of ks = 0.10 mm (fine but catchy microstructure) and 0-0.1 mm/d at ks 1.25 mm (wavy microstructure) at steady state and transient discharge within the first 28 days after sewer cleaning.

Highly icephobic properties on slippery surfaces formed from polysiloxane and fluorinated POSS

Recent emerging strategies to prepare icephobic coatings have focused on slippery surfaces containing a liquid lubricant with low surface energy, which significantly reduces ice adhesion. In this work, a facile technique was developed for preparation of polysiloxane coatings with efficient and durable icephobicity. Fluorinated polyhedral oligomeric silsesquioxanes (F-POSS-SiH) with different fluorinated groups and Si-H active sites were synthesized via hydrosilylation between fluorinated methacrylates and octakis(dimethylsiloxy) octasilsequioxane. The F-POSS-SiH hybrid compound was subsequently applied as a co-crosslinker in the system of polymethylhydrosiloxane (PMHS) and polymethylvinylsiloxane to create silicone coatings. The low surface energy of fluorinated groups could drive F-POSS-SiH towards the coating surface, leading to a gradient distribution in which F-POSS-SiH was self-assembled on the top surface, while silicone was rich in the bottom layer. Meanwhile, wavy surfaces were generated spontaneously by compressive stress during the coating formation. The wavy microstructure of coatings provided space for the unreacted silicone oil, i.e., low molecular weight PMHS, that could be considered as a liquid lubricant and controlled by the dosage. Therefore, the slippery wavy coatings showed highly icephobic properties with extraordinarily low ice shear strengths at a lowest value of 3.8 ± 1.8 kPa, only 5 percentage of Sylgard 184. Moreover, the coatings remained icephobicity after 15 icing/deicing cycles, demonstrating excellent durability.

A theoretical and experimental investigation of orthogonal slow tool servo machining of wavy microstructured patterns on precision rollers

Precision cylinders, or rollers, with patterned microstructures on the surface are the key tooling component in the Roll-to-Roll and Roll-to-Plane fabrication process for precision manufacturing of microstructured plastic films. These films are widely used in optical applications such as the backlight guide and brightness enhancement films in LCD and LED displays. Compared with other fabrication processes, such as lithography, Single-Point Diamond Turning (SPDT), using a Fast Tool Servo (FTS) or Slow Tool Servo (STS) process, is an enabling and efficient machining method to fabricate microstructures. Most studies of the tool servo machining process focus on either machining microstructures in the axial direction for face machining of flat parts or in the radial direction on the surface of a precision roller. There is relatively little research work found on the machining of patterned microstructures on the surface of precision rollers using the tool servo in the axial direction. This paper presents a pilot study on the development of a tool path generator for machining wavy microstructure patterns on precision rollers by using an Orthogonal Slow Tool Servo (OSTS) process. The machining concept of OSTS is first explained, and then the tool path generator is developed in detail for machining wavy microstructure patterns on a roller surface. Modelling and simulation of pattern generation for different microstructures with different wavy patterns and grooves are presented based on the proposed tool path generator. Preliminary experimental work using SPDT on a 4-axis ultra-precision machine tool is presented and clearly shows the generation of unique wavy microstructure patterns on a precision roller. The machined wavy microstructures on the roller surface are measured and analyzed to evaluate the validity of the proposed tool path generator.

Fabrication of a seamless roller mold with wavy microstructures using mask-less curved surface beam pen lithography

Roller imprinting is one of the most commonly used methods for the fabrication of continuous functional structures over large areas. However, the fabrication of roller molds with seamless and complex patterns poses a significant challenge. This paper presents an innovative technique for fabricating a seamless roller mold with wavy microstructures using a novel mask-less curved surface beam pen lithography technique. The major steps in the proposed technique include spray coating a thin photo-resist (PR) layer on the roller, exposing the PR layer though a translating micro-lens array (MLA), etching the patterned PR layer, and electro-polishing the etched microstructures. The proposed method is used to pattern roller molds with different wavy microstructures by varying the rotation speed of the roller, the translation speed of the MLA holder, and the translation distance of the MLA holder. The patterned metal roller molds are then used to replicate wavy microstructures on a thin polyethylene terephthalate substrate by means of continuous UV-type roller imprinting methods. The line-width and height of the wavy microstructure are 84.5 µm and 25.5 µm, respectively.

A wavy graphene/platinum hybrid with increased electroactivity for the methanol oxidation reaction

Two distinct graphene sheets, highly flat graphene and wavy graphene, were used as support materials for in situ nucleation and growth of platinum nanoparticles (Pt NPs) to synthesize graphene/Pt catalysts. The average size of Pt NPs on the wavy graphene sheets is around 2 nm and is smaller than those on the flat graphene sheets. The electrochemical activity of the two as-prepared catalysts towards methanol oxidation was investigated and compared with that of a commercial Pt/carbon black (Pt/C) catalyst, and electrochemical results showed that the wavy graphene/Pt catalyst possessed the best poison tolerance and comparable electrochemical surface area to the commercial Pt/C catalyst. The wavy microstructure is believed to be responsible for the stable dispensability of the as-prepared wavy graphene and the acquisition of small size Pt NPs, since the abundant ripples coming from the wavy microstructure effectively prevent the aggregation of the graphene sheets, and also act as barriers to prevent agglomeration of Pt NPs during their in situ nucleation and growth process. This work indicates that the microstructure of the supporting material plays a crucial role in the electrochemical performance of platinum-based catalysts.

A multi-scale, discrete-cell simulation of organogenesis: Application to the effects of strain stimulus on collective cell behavior during ameloblast migration

A multi-scale strategy is presented for simulating organogenesis that uses a single cell response function to define the behavior of individual cells in an organ-scale simulation of a large cell population. The response function summarizes detailed information about the behavior of individual cells in a sufficiently economical way that the organ-scale model can be commensurate with the entire organ. The first application demonstrates the effects of strain stimulus on the migration of ameloblasts during enamel formation. Ameloblasts are an attractive study case because mineralization preserves a complete record of their migratory paths. The response function in this case specifies the motions of cells responding to strain stimuli that propagate through the population. The strain stimuli are related to the curvature of the surface from which the ameloblasts migrate (the dentin–enamel junction or DEJ). A single unknown rate parameter is calibrated by an independent datum from the human tooth. With no remaining adjustable parameters, the theory correctly predicts aspects of the fracture-resistant, wavy microstructure of enamel in the human molar, including wavelength variations and the rate of wave amplitude damping. At a critical value of curvature of the DEJ, a transition in the ordering of cells occurs, from invariant order over the whole population to self-assembly of the population into groups or gangs. The prediction of an ordering transition and the predicted critical curvature are consistent with gnarled enamel in the cusps of the human molar. The calibration of the model using human data also predicts waves in the mouse incisor and an ordering transition at the chimpanzee cingulum. Widespread compressive strain is predicted late in the migration for both the human molar and mouse incisor, providing a possible signal for the termination of amelogenesis.

Thermo-elastic moduli of periodic multilayers with wavy architectures

The recently developed parametric finite-volume direct averaging micromechanics theory for periodic materials is employed to investigate the effective moduli and thermal expansion coefficients of lamellar composites with wavy architectures. In the parametric version, a reference square subvolume is mapped onto a quadrilateral subvolume in the actual discretized microstructure to accurately capture the in situ microstructural details. The mapping is used to construct local stiffness matrices of quadrilateral subvolumes which are employed in the local/global stiffness matrix solution strategy for the unit cell problem within a homogenization framework. Complete set of homogenized moduli and thermal expansion coefficients of multilayers comprised of alternating soft and hard laminae with two types of waviness is generated for the first time as a function of the volume content of the hard phase for two amplitude-to-wavelength ratios. The observed changes in the homogenized mechanical and thermal properties relative to the reference flat-layer configuration depend on the wavy microstructure orientation and become greater with increasing amplitude-to-wavelength ratios. Examination of local stress fields explains the differences observed in the homogenized moduli of multilayers with sinusoidal and corrugated waveforms for the two amplitude-to-wavelength ratios.