Fabrication of weaved ceramic mesh from green microfibers based on cross-flow microfluidics

Microfibers-weaved ceramic filters are in increasing demand due to their high filtration efficiency, stable structure and remarkable ceramic properties in water and gas treatment. To date, it remains a challenge to find an effective way to weave ceramic microfibers. This work demonstrates a novel strategy that combines gel-casting and in situ cross-flow microfluidic molding to fabricate highly flexible and shape-retentive green microfibers and then weaves them before sintering. By tailoring the curing temperature and flow rate, the diameter and surface morphology of the microfiber is accordingly tuned. Besides mesh structure, the microfibers can also be weaved into more complex three-dimensional structures such as dragonfly knot, Chinese knot, etc. Benefitting from the widely used solution system and microfluidic method, this system can serve as a general and stable platform for preparing microfibers-weaved ceramic filters made from different materials, thus holds great potential in a wide range of working conditions.     

Fabrication of crescent-shaped ceramic microparticles based on single emulsion microfluidics

Ceramic microparticles have great potentials in various fields such as materials engineering, biotechnology, microelectromechanical systems, etc. Morphology of the microparticle performs an important role on their application. To date, it remains difficult to find an effective and controllable way for fabricating nonspherical ceramic microparticles with 3D features. This work demonstrates a method that combines UV light lithography and single emulsion opaque-droplet-templated microfluidic molding to prepare the crescent-shaped ceramic microparticles. By tailoring the intensity of UV light and flow rate of fluid, the shapes of microparticles are accordingly tuned. Therefore, varieties of crescent-shaped microparticles and their variations have been fabricated. After sintering, the crescent-shaped alumina ceramic microparticles were obtained. Benefitting from the light absorption and scattering behavior of most ceramic nanoparticles, this system can serve as a general platform to produce crescent-shaped microparticles made from different materials, and hold great potentials for applications in microrobotics, structural materials in MEMS, and biotechnology.     

Studies of acoustical absorption of flexible polyurethane foam

It was confirmed that one of the principal factors which influences the acoustical absorption of flexible polyurethane foam is flow resistance of foam. Normal polyester-based flexible polyurethane foam itself has an adequate value of flow resistance and shows fairly good sound absorption. Acoustical absorption of normal polyether-based flexible polyurethane foam, which generally has lower flow resistance, can be improved by using some expedients such as setting up a certain skin layer on the foam surface so that the flow resistance of the foam can be increased. Surface treatment of foam such as gluing film, heat melting, spraying, or heat adhesion with film can not only improve sound absorption and mechanical properties of polyether-based flexible polyurethane foam, but also improve the hydrolysis resistance of polyester-based flexible polyurethane foam. Inserting some metal foil or plastic film between flexible polyurethane foams can change the sound absorption behavior according to the position of the foil or the film in the foam. The effects of foam thickness, existence of air layer behind foam, and foam profiling on acoustic absorption were also investigated.     

MOISTURE EXPANSION OF GLAZES AND OTHER CERAMIC FINISHES1

Research for ascertaining why some glazes are more resistant to “moisture crazing” than others revealed the fact that certain glazes expand, because of the action of water, similarly to some of the ceramic bodies t o which they are applied. Although a control of this type of expansion is very important in fitting glazes to bodies, it has not been previously considered. Its importance should be evident at once when it is considered that a large “moisture expansion” in a glaze or other finish is in many cases an indication that the glaze will not be so liable to craze when the ceramic ware or material on which it is used is exposed to moisture. This follows since the glaze and the body on which it goes and which is ordinarily very susceptible to this kind of expansion will then increase in size simultaneously and more nearly at the same rate. Such conditions lessen the tendency of the body expansion to cause tensile stresses in the glaze. In this investigation specimens of various finishes were subjected to steam at 150 pounds per square inch for an hour because it was known that this treatment of such materials produces effects similar to those caused by long exposure to weather. This artificial weathering treatment caused in lustrous glazes an average expansion of 0.004%, in mat glazes 0.011%, in vitreous slip finishes 0.005%, and in porous slip finishes 0.033%. The moisture expansion of one of the mat glazes was 30% of the average obtained for a ceramic body having an absorption of approximately 12%. This proclivity of ceramic finishes to expand by the absorption of moisture can be controlled in their manufacture.     

Ionic liquids enhanced performance of PVC gels actuator

Stimulated devices are highly demanded for actuators and artificial muscles in the recent era but susceptible to low deformation at an applied voltage. In the present work, ionic liquids (ILs) based gel films were prepared from the polyvinyl chloride (PVC), dibutyl adipate (DBA), 1-butyl, 3-methimidazolium chloride, and 1-pentyl-3-methylimidazolium hexafluorophosphate by a simple solvent evaporation method. The structural, morphological, optical, and mechanical properties of the composite PVC/ILs gel were characterized by Fourier-transform infrared spectroscopy (FTIR), Large Angle X-ray scattering (LAXS), UV–visible (UV–vis) absorption spectroscopy, scanning electron micrpscopy (SEM) and elemental mapping. We found that the displacement of plasticized PVC gels-based actuator was 0.1 mm with the response time of 0.33 s at an induced voltage of 1000 V. The loading of 0.02% of IL (fluorides) with PVC gel showed maximum deformation of 0.16 mm with a relatively rapid response time of 0.2 s. These high deformation and response time values of IL fluoride-based gels are dramatically higher than reported PVC gels. Likewise, the loading of IL fluorides in the PVC gel showed a high elongation value at the break of about 377%. This work suggests that the flexible gel based on IL fluorides and PVC could be a potential candidate for the fabrication of high-performance artificial muscles and tunable soft actuators.     

Flow control in paper-based microfluidic device for automatic multistep assays: A focused minireview

Although lateral flow tests (LFTs) are easy-to-use diagnostics, they have fundamental limitations for sequential multistep assay that can be reduced to a single chemical reaction step. Paper-based microfluidic devices have attracted considerable attention for use in automatic multi-step assays because paper can be an excellent platform to control sequential fluid flow without external equipment. This review focuses on recent developments on how to control flow rate in paper-based microfluidic devices for automating sequential multi-step assays. The aim of this review is to discuss the limitations of LFTs and potential paper-based microfluidic devices for automated sequential multi-step assays in developing countries; and the existing fluidic control technologies for sequential multi-step assays. In addition, we present future challenges for commercialization of paper-based microfluidic devices to perform automatic multi-step assays.     

Droplet‐Shooting and Size‐Filtration (DSSF) Method for Synthesis of Cell‐Sized Liposomes with Controlled Lipid Compositions

We report a centrifugal microfluidic method, droplet‐shooting and size‐filtration (DSSF), for the production of cell‐sized liposomes with controlled lipid compositions. This involves the generation of large and small droplets from the tip of a glass capillary and the selective transfer of small droplets through an oil‐water interface, thus resulting in the generation of cell‐sized liposomes. We demonstrate control of the microdomain formation as well as the formation of asymmetric lipid bilayer liposomes of uniform size by the control of lipid composition. The DSSF method involves simple microfluidics and is easy to use. In addition, only a small volume (0.5–2 μL) of sample solution is required for the formation of hundreds of cell‐sized liposomes. We believe that this method can be applied to generate cell‐sized liposomes for a wide variety of uses, such as the construction of artificial cell‐like systems.     

A MONTE-CARLO APPROACH TO THE INTERPRETATION OF BUBBLE PROBE SIGNALS IN FREELY BUBBLING FLUID BEDS†

The interpretation of the signals generated by a double probe may be done by the three characteristic times method:

t₁ the time duration of the pulses;

t₂ the time shift between the signals of the two probes;

t₃ the time interval between two pulses on one channel.

Each of these times is largely dispersed and the corresponding histograms may be constructed.

The present work is a trial to go over from the time histograms to physical properties of the bubbles combining a Monte-Carlo simulation and a flexible simplex optimisation procedure.

As a result, the percentage of oblique bubbles cutting just one level, the bubble size distribution, the average velocity-size relation, and the individual dispersion around it may be defined.

The procedure is finally applied to experimental results obtained with a light probe in a fluid bed of glass beads.     

双重乳液的微流控制备进展

双重乳液是一种离散相液滴中还包裹着更小的液滴的高度结构化流体,单分散的在食品、化工、医疗等领域有着广泛的应用。微流控技术作为一门研究微尺度流体的新兴技术,已经成为制备优质双重乳液的首选。本文对被动式微流控技术进行了系统地综述,介绍了协流式、交叉流式、流动聚焦式微通道的结构及其乳化机理,展望了该项技术在微液滴制备方面的发展前景。在学科交叉应用的背景下,通过对微流控装置的改进与升级,可以克服常见微流控方法出现的双乳液生产效率低,不具备超薄壁结构等问题。此外,本文还讨论了微流控技术背景下双重乳液流型演化研究的进展,提出可以通过单乳液的研究基础,联系和发展双重乳液流型演化的完备理论体系。     

Microfluidic etching for fabrication of flexible and all-solid-state micro supercapacitor based on MnO2 nanoparticles

Micro-supercapacitors are a promising candidate whose reliability and performances are struggling to meet the energy demands dictated by the incoming generation of miniaturized electronic devices. In this paper, we describe a facile and low-cost method for fabricating flexible and all-solid-state micro supercapacitors by microfluidic etching. The micro-supercapacitor configuration is composed of sub-10-nm-scale MnO(2) nanoparticle interdigital microelectrode fingers prepared by microfluidic etching with H(3)PO(4)-PVA thin films as both the solid-state electrolyte and the flexible substrate. The entire device shows outstanding electrochemical performances with high specific capacitance and stable cycle life, and the performance can be mostly preserved even conditions of under repeated bending. The technique we describe here is a universal method for fabricating a micro-supercapacitor, since the microfluidic etching can be extended to most active materials which can be used for energy- and power-devices, and there are many other choices for the solid electrolyte. Thus, these micro-supercapacitors provide a promising power source in microelectromechanical systems (MEMS), wearable electronics and other general requirements.     

Using hot-vapor bypass for pressure control in distillation columns

Distillation column control is widely explored in literature due to its complexity and importance in chemical and petrochemical industries.In this process,pressure represents one of the most important variables to be controlled.However,there are few studies about how pressure affects the dynamic behavior of distillation columns and most research on distillation column control involve direct manipulation of cooling fluid through the condenser.Nevertheless,such an approach demands constant changes in cooling fluid flowrates that are commonly by the order of tons per hour,which can be difficult to work or even unfeasible in a real plant.Furthermore,this strategy is usually avoided,as it can cause fouling and corrosion acceleration.The hot-vapor bypass strategy fits well as a solution for these issues,eliminating the need to dynamically manipulate cooling fluid flowrates in the condensation unit.This work presents the modeling and simulation of a conventional distillation column for the separation of water and ethanol,in which a comparative study between a conventional pressure control and a control using hot-vapor bypass was performed.The main results were obtained through dynamic simulations which considered various disturbances in the feed stream,and demonstrated superior performance by the hot-vapor bypass system over the usual scheme proposed in literature,while evaluating the Integral Absolute Error (IAE) norm as the control performance index.     

Neural Networks for Chemical Engineering Unit Operations

Application of artificial neural networks in simulation of chemical engineering unit operations are studied. On the basis of the present work it is suggested that the raw data describing the phenomenon should be processed so that the relationships of the input variables are studied and if relationships are found, such as dimensionless numbers, these relationships are set as inputs in the neural network. Further, if the phenomenon can be described by a simplified mathematical expression, the value calculated by such simplified solution is set as one of the inputs. The method is demonstrated by three examples, namely, by turbulent fluid flow in a tube, breakthrough curve of adsorption, and by suspension crystallization. In all cases the method presented in this work results in a more accurate simulation and in easier training of the neural network.     

Recent developments in scale-up of microfluidic emulsion generation via parallelization

Microfluidics affords precise control over the flow of multiphasic fluids in micron-scale channels. By manipulating the viscous and surface tension forces present in multiphasic flows in microfluidic channels, it is possible to produce highly uniform emulsion droplets one at a time. Monodisperse droplets generated based on microfluidics are useful templates for producing uniform microcapsules and microparticles for encapsulation and delivery of active ingredients as well as living cells. Also, droplet microfluidics have been extensively exploited as a means to enable highthroughput biological screening and assays. Despite the promise droplet-based microfluidics hold for a wide range of applications, low production rate (<<10mL/hour) of emulsion droplets has been a major hindrance to widespread utilization at the industrial and commercial scale. Several reports have recently shown that one way to overcome this challenge and enable mass production of microfluidic droplets is to parallelize droplet generation, by incorporating a large number of droplet generation units (N>>100) and networks of fluid channels that distribute fluid to each of these generators onto a single chip. To parallelize droplet generation and, at the same time, maintain high uniformity of emulsion droplets, several considerations have to be made including the design of channel geometries to ensure even distribution of fluids to each droplet generator, methods for large-scale and uniform fabrication of microchannels, device materials for mechanically robust operation to withstand high-pressure injection, and development of commercially feasible fabrication techniques for three-dimensional microfluidic devices. We highlight some of the recent advances in the mass production of highly uniform microfluidics droplets via parallelization and discuss outstanding issues.     

Temperature effects during practical operation of microfluidic chips

The temperature dependent fluorescence of Rhodamine B was used to investigate the temperature effect of several system parameters in a microfluidic chip. This was combined with computational fluid dynamics calculations. Limited air movement over the chip had no significant effect on the temperature of the fluid running through the chip. Also, fluid flow through the channels at had no effect on the chip temperature or heating and cooling dynamics. The temperature varied greatly over the length of the chip. During transient operation of the chip, the heat up and cool down rates varied over the chip, and were dependent on the distance to the heater. The thermal time constant for heat up was four to five times lower than for cool down. The results can be used as tools for operating a temperature controlled microfluidic chip.     

Preparation of multifunctional self-healing MXene/PVA double network hydrogel wearable strain sensor for monitoring human body and organ movement

In this work, a kind of conductive, self-healing hydrogel was prepared. Then it is assembled into a flexible wearable sensor for human motion detection and human-computer interaction. MXene/PVA-CBA hydrogel has super mechanical properties and excellent self-healing ability (1.8 s). It is assembled into a flexible sensor with high sensitivity, which can accurately detect various movements of the human body (ranging from frowning, speaking, and coughing on the face to bending of fingers and wrists, and body movements). Furthermore, it can be used for handwriting recognition. When it is installed on the artificial limb, it can realize the function of touching the capacitive screen. It solves the problem of using silicone prostheses to control the screen and has broad research potential in the field of intelligent robots. Therefore, the flexible wearable sensor composed of MXene/PVA-CBA hydrogel has great potential in human motion detection, bionic intelligent robot, and intelligent detection.     

A MONTE-CARLO APPROACH TO THE INTERPRETATION OF BUBBLE PROBE SIGNALS IN FREELY BUBBLING FLUID BEDS†

The interpretation of the signals generated by a double probe may be done by the three characteristic times method:

t₁ the time duration of the pulses;

t₂ the time shift between the signals of the two probes;

t₃ the time interval between two pulses on one channel.

Each of these times is largely dispersed and the corresponding histograms may be constructed.

The present work is a trial to go over from the time histograms to physical properties of the bubbles combining a Monte-Carlo simulation and a flexible simplex optimisation procedure.

As a result, the percentage of oblique bubbles cutting just one level, the bubble size distribution, the average velocity-size relation, and the individual dispersion around it may be defined.

The procedure is finally applied to experimental results obtained with a light probe in a fluid bed of glass beads.     

Rushton桨搅拌槽内轴弯矩的数值模拟

针对搅拌槽内流体流动、柔性结构振动和流动流体与柔性结构相互作用(流固耦合)的特征,分别采用计算流体动力学(不考虑结构振动)、计算结构动力学(不考虑流体作用)和两种计算动力学相互瞬态耦合模拟(同时考虑结构振动和流体作用)研究Rushton桨搅拌轴的弯矩幅值平均和波动特性。研究结果表明:搅拌槽内流体充当了振动的阻尼作用,抑制了搅拌桨轴侧向振动的幅度,但主体流动的低频宏观不稳定性显著地增加了搅拌桨轴旋转的不稳定性,同时搅拌桨轴侧向振动增加了搅拌桨叶片上的流体载荷不稳定性,但对不均衡性影响很小;弯矩流体成分(来源于流体压力和粘性力)与结构成分(来源于结构重力和惯性力)之间夹角是随机的,但平均夹角接近于90°;耦合模拟结果与实验数据吻合较好,且明显优于计算流体动力学和计算结构动力学分离模拟计算结果。研究结果有助于深入理解搅拌槽内流固耦合对搅拌轴弯矩的影响,对搅拌设备的机械设计具有指导意义。     

On developing a novel mixed-unit microparticle system for controlled release

In this study, uniform microparticles were prepared using the highly efficient microfluidic spray drying technology, and then a flexible controlled release mixed-unit microparticle system was developed to meet various needs. A mathematical drug release model of the mixed system was established and two mixed formulations were used to testify the predictive ability when initial parameters were given. Results have proved that the proposed model could precisely predict the release rate of tested samples. In conclusion, the novel system for controlled release may provide a new option for modified release drugs and may have a good prospect in the industrial application.     

Iron and zinc in vitro potential availability in an infant diet with fortified bread with different iron sources or with the addition of different iron absorption promoters

Home-made diets are the most frequently used complementary foods. In the present work we evaluated iron and zinc availability in a usually consumed infant diet containing either iron-fortified bread with different iron sources: ferrous sulfate, ferrous bisglycinate, NaFeEDTA. We also used non-fortified bread with absorption promoters: ascorbic acid, sodium citrate, Na2EDTA, combined with different beverages. The diet (potato, pumpkin, grits, bread, and apple) was combined with water, milk, tea, a soft drink and an orange-based artificial drink. Mineral dialyzability (D) as an indicator of potential availability was determined using an in vitro method. Statistical analysis was performed by ANOVA, and a posteriori Tukey test. There were no significant differences in FeD between diets with ferrous sulfate or ferrous bisglycinate fortified bread; in NaFeEDTA fortified bread it increased significantly (p<0.05). Iron D increase was greater in diets with bread containing absorption promoters than in those with fortified bread. The orange-based artificial drink increased FeD, while tea and milk decreased it significantly (p < 0.05). Zinc D increased significantly when the bread was fortified either with ferrous sulfate or NaFeEDTA, but remained unchanged in diets with ferrous bisglycinate fortified bread. The addition of tea or milk decreased ZnD while the orange-based artificial drink increased it significantly (p < 0.05). Regarding absorption promoters, the greater values both in FeD and ZnD were observed in diets with iron nonfortified bread containing Na2EDTA.     

Effect of viscoelasticity on drop dynamics in 5:1:5 contraction/expansion microchannel flow

Recently, we reported how viscoelasticity affects drop dynamics in a microchannel flow using the finite element-front tracking method (FE-FTM). In this work, we investigate drop dynamics for a wider range of parameters: viscosity ratio between droplet and medium (χ), capillary number (Ca), droplet size, and fluid elasticity. The Oldroyd-B model is adopted as the constitutive equation for the viscoelastic fluid. We observe that the drop deformation in a microfluidic channel is dependent on Ca, which is more pronounced for smaller χ values. The present work shows that viscoelasticity plays an important role in drop dynamics with increasing χ values for Newtonian droplet in viscoelastic medium, which can be attributed to high normal stress developed in narrow film thickness between droplet and channel for higher χ values. We also study circulation problem inside droplets, which is important in practice, such as in droplet reactor application. The present work shows that circulation intensity is enhanced with decreasing χ values. We find that the relevance of viscoelastic effects on internal circulation is dependent on χ values, and the circulation intensity is distinctively decreased with increasing elasticity for high χ values for Newtonian droplet in viscoelastic medium. We expect that the present work be helpful not only in controlling droplets but also to improve our physical insight on drop dynamics in microchannel flows.