scholarly journals Microfluidic conformal coating of non-spherical magnetic particles

2021 ◽  
Author(s):  
Byeong-Ui Moon ◽  
Navid Hakimi ◽  
Dae Kun Hwang ◽  
Scott S. H. Tsai
Keyword(s):  
Thin Film ◽  
Interfacial Tension ◽  
Magnetic Particles ◽  
Magnetic Field Gradient ◽  
Interfacial Area ◽  
Aqueous Fluid ◽  
Microfluidic System ◽  
Immiscible Fluids ◽  
Spherical Particles ◽  
Conformal Coating

We present the conformal coating of non-spherical magnetic particles in a co-laminar flow microfluidic system. Whereas in the previous reports spherical particles had been coated with thin films that formed spheres around the particles; in this article, we show the coating of non-spherical particles with coating layers that are approximately uniform in thickness. The novelty of our work is that while liquid-liquid interfacial tension tends to minimize the surface area of interfaces—for example, to form spherical droplets that encapsulate spherical particles—in our experiments, the thin film that coats non-spherical particles has a non-minimal interfacial area. We first make bullet-shaped magnetic microparticles using a stop-flow lithography method that was previously demonstrated. We then suspend the bullet-shaped microparticles in an aqueous solution and flow the particle suspension with a co-flow of a non-aqueous mixture. A magnetic field gradient from a permanent magnet pulls the microparticles in the transverse direction to the fluid flow, until the particles reach the interface between the immiscible fluids. We observe that upon crossing the oil-water interface, the microparticles become coated by a thin film of the aqueous fluid. When we increase the two-fluid interfacial tension by reducing surfactant concentration, we observe that the particles become trapped at the interface, and we use this observation to extract an approximate magnetic susceptibility of the manufactured non-spherical microparticles. Finally, using fluorescence imaging, we confirm the uniformity of the thin film coating along the entire curved surface of the bullet-shaped particles. To the best of our knowledge, this is the first demonstration of conformal coating of non-spherical particles using microfluidics.

scholarly journals Interfacial Tension Measurements in Microfluidic Quasi-Static Extensional Flows

Micromachines ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 272
Author(s):  
Doojin Lee ◽  
Amy Q. Shen
Keyword(s):  
Interfacial Tension ◽  
Microfluidic Device ◽  
Extensional Flow ◽  
Immiscible Fluids ◽  
Droplet Microfluidics ◽  
Channel Height ◽  
Deformation Model ◽  
Droplet Deformation ◽  
Extensional Flows ◽  
2D Model

Droplet microfluidics provides a versatile tool for measuring interfacial tensions between two immiscible fluids owing to its abilities of fast response, enhanced throughput, portability and easy manipulations of fluid compositions, comparing to conventional techniques. Purely homogeneous extension in the microfluidic device is desirable to measure the interfacial tension because the flow field enables symmetric droplet deformation along the outflow direction. To do so, we designed a microfluidic device consisting of a droplet production region to first generate emulsion droplets at a flow-focusing area. The droplets are then trapped at a stagnation point in the cross junction area, subsequently being stretched along the outflow direction under the extensional flow. These droplets in the device are either confined or unconfined in the channel walls depending on the channel height, which yields different droplet deformations. To calculate the interfacial tension for confined and unconfined droplet cases, quasi-static 2D Darcy approximation model and quasi-static 3D small deformation model are used. For the confined droplet case under the extensional flow, an effective viscosity of the two immiscible fluids, accounting for the viscosity ratio of continuous and dispersed phases, captures the droplet deformation well. However, the 2D model is limited to the case where the droplet is confined in the channel walls and deforms two-dimensionally. For the unconfined droplet case, the 3D model provides more robust estimates than the 2D model. We demonstrate that both 2D and 3D models provide good interfacial tension measurements under quasi-static extensional flows in comparison with the conventional pendant drop method.

The Analysis on the Starting Friction Torque Increase of Magnetic Fluid Revolving Sealing

2013 ◽  
Vol 275-277 ◽  
pp. 429-432 ◽  
Author(s):  
Yu Qiang Cai ◽  
Na Xing
Keyword(s):  
Magnetic Fluid ◽  
Magnetic Particles ◽  
Influence Factor ◽  
Magnetic Field Gradient ◽  
Friction Torque ◽  
Key Factor ◽  
Lower Temperature ◽  
Change Of Microstructure ◽  
Starting Torque ◽  
Main Influence

Abstract. Magnetic fluid revolving sealing is widely used in modern industry. In the process of application, it is founded that the starting friction torque is very large, particularly at lower temperature. This problem has become a key factor restricting the application of magnetic fluid rotation sealing. In this paper, the mechanism of starting torque increase is analyzed, based on the change of microstructure and its viscosity. After analysis , such conclusion is obtained , which can be described: to a certain sealing structure, the type of magnetic fluid, size distribution of magnetic particles as well as the working condition concluding temperature, magnetic field gradient and the revolving velocity of shaft is the main influence factor of starting friction torque . It is very useful to reduce the starting friction torque.

Overcoats and Lubrication for Thin Film Disks

MRS Bulletin ◽  
1990 ◽  
Vol 15 (3) ◽  
pp. 45-52 ◽  
Author(s):  
A.M. Homola ◽  
C.M. Mate ◽  
G.B. Street
Keyword(s):  
Thin Film ◽  
Data Storage ◽  
Magnetic Particles ◽  
Areal Density ◽  
Magnetic Film ◽  
Alloy Thin Film ◽  
Magnetic Media ◽  
Disk Interface ◽  
Storage Devices ◽  
Particulate Media

Metallic alloy thin film media and ever decreasing head-to-media spacing make severe demands on storage devices. Decreasing head-to-media separation is critical for high storage densities but it also leads to increased slider-disk interactions, which can cause slider and disk wear or even head crashes. Wear can also occur when drives start and stop when the slider contacts the disk at relatively high speeds. The reliability and durability of thin film disks, which provide much higher areal density than conventional oxide disks with particulate media, are achieved by the use of very thin overcoat materials and surface lubricants. This article summarizes the approaches taken in the industry to enhance the tribological performance of magnetic media, with special emphasis on the basic understanding of the processes occurring at the slider-disk interface.The continuous rise in the demand for storage capacity at a competitive price is the prime motivator of the changes we have seen in the data storage industry. It is clearly stimulating the present move away from particulate media, which has long dominated all fields of data storage, i.e., tape, rigid, and flexible disks, to the thin film storage media. Particulate storage devices use magnetic media formulated by dispersing magnetic particles, usually iron oxides, in an organic binder. In thin film storage devices, the storage medium is a continuous magnetic film, usually a cobalt alloy, made either by sputtering or by electroless plating.

scholarly journals Annular Thin-Film Flows Driven by Azimuthal Variations in Interfacial Tension

2009 ◽  
Vol 62 (4) ◽  
pp. 403-430 ◽  
Author(s):  
L. R. Band ◽  
D. S. Riley ◽  
P. C. Matthews ◽  
J. M. Oliver ◽  
S. L. Waters
Keyword(s):  
Thin Film ◽  
Interfacial Tension ◽  
Film Flows

scholarly journals Synthesis Features of Iron Oxide Nanopowders with High Magnetic and Sorption Properties

2018 ◽  
Vol 915 ◽  
pp. 116-120
Author(s):  
Sergiy Lavrynenko ◽  
Athanasios G. Mamalis ◽  
Dmitry Sofronov ◽  
Alexandra Odnovolova ◽  
Vadym Starikov
Keyword(s):  
Phase Composition ◽  
Magnetic Particles ◽  
Deposition Process ◽  
Spherical Particles ◽  
Sorptive Capacity ◽  
Extraction Separation ◽  
Average Size ◽  
Increasing Temperature ◽  
Magnetite Phase ◽  
Purification Of Water

The magnetic particles of iron oxides are promising materials for the purification of water from ions of heavy metals and radionuclides. Their advantage compared to other sorbents is the ability to extract by applied magnetic field, which greatly simplifies the task of extraction, separation and processing in cleaning technologies. The aim of this work is investigation of temperature and concentration of iron in the solution effect on the phase composition, nanoparticle size and their magnetization. Phase magnetite in the sample increases with increasing temperature and the magnetization decreases slightly with increasing the initial concentration of iron in solution. We found that regardless of the conditions of deposition formed spherical particles whose average size ranges from 7 to 15 nm. The sorptive capacity of the particles is virtually independent of the phase composition and for cobalt is about 18 mg/g. For sorption-based material magnetic particles Fe3O4 recommended to carry out the deposition process at a temperature not lower than 80°C. The concentration of iron in solution must be within 0,15–0,3M. The particles obtained contain in their composition at least 90 wt.% of magnetite phase and are characterized by a magnetization in the range of 65–70 A·m2/kg. Also in the paper is comparing efficiency of extraction and sorption capacity for cobalt particles by different phase of magnetite and hematite.

Retrogressive fluids and vein formation during uplift of the Priestley metamorphic complex, north Victoria Land, Antarctica

1995 ◽  
Vol 7 (3) ◽  
pp. 283-291 ◽  
Author(s):  
D. Craw ◽  
Y.A. Cook
Keyword(s):  
Fluid Pressure ◽  
Aqueous Fluid ◽  
Immiscible Fluids ◽  
Greenschist Facies ◽  
Metamorphic Complex ◽  
Brittle Ductile Transition ◽  
Vein Formation ◽  
Victoria Land ◽  
Primary Fluid ◽  
Phase Fluid

The poly-deformed Priestley schist (Wilson Terrane) of north Victoria Land, Antarctica ranges in metamorphic grade from lower greenschist facies to upper amphibolite facies. All grades of schist have been affected by structurally controlled retrogressive H2O-CO2 fluids with 45–70 mole % CO2. The fluids have deposited quartz-carbonate veins with pyrite and chlorite or biotite in late stage structures. Veins typically constitute < 1% of the rock mass, but in one greenschist facies area > 10% of the rock is vein. Veins in higher grade schists have been boudinaged after formation, and many have been annealed. Primary fluid inclusions are preserved in veins in biotite zone schists in two localities. At one locality, entrapment of immiscible fluids (water with c. 8 and 45 mole % CO2) occurred during vein formation, at about 280–300°C and 700 ± 200 bars fluid pressure. The aqueous fluid is slightly saline (4 wt % NaCl equivalent). At the other primary fluid inclusion locality, veins were formed from a single phase fluid (c. 70 mole % CO2) at 200–350°C and 1600 ± 500 bars fluid pressure. Both these vein systems are inferred to have formed between 2 and 8 km depth, near the brittle-ductile transition. Retrogressive fluid mobility and vein formation occurred throughout schist in the Priestly metamorphic complex during uplift in the latter part of the Ross Orogeny (c. 490 Ma), following near-isobaric cooling at metamorphic depths.

The effects of surfactants on drop deformation and breakup

1990 ◽  
Vol 220 ◽  
pp. 161-186 ◽  
Author(s):  
H. A. Stone ◽  
L. G. Leal
Keyword(s):  
Equation Of State ◽  
Interfacial Tension ◽  
Active Material ◽  
Interfacial Area ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Drop Deformation ◽  
Local Concentration ◽  
Interfacial Velocity ◽  
Surface Active

The effects of surface-active agents on drop deformation and breakup in extensional flows at low Reynolds numbers are described. In this free-boundary problem, determination of the interfacial velocity requires knowledge of the distribution of surfactant, which, in turn, requires knowledge of the interfacial velocity field. We account for this explicit coupling of the unknown drop shape and the evolving surfactant distribution. An analytical result valid for nearly spherical distortions is presented first. Finite drop deformation is studied numerically using the boundary-integral method in conjunction with the time-dependent convective–diffusion equation for surfactant transport. This procedure accurately follows interfacial tension variations, produced by non-uniform surfactant distribution, on the evolving interface. The numerical method allows for an arbitrary equation of state relating interfacial tension to the local concentration of surfactant, although calculations are presented only for the common linear equation of state. Also, only the case of insoluble surfactant is studied.The analytical and numerical results indicate that at low capillary numbers the presence of surfactant causes larger deformation than would occur for a drop with a constant interfacial tension equal to the initial equilibrium value. The increased deformation occurs owing to surfactant being swept to the end of the drop where it acts to locally lower the interfacial tension, which therefore requires increased deformation to satisfy the normal stress balance. However, at larger capillary numbers and finite deformations, this convective effect competes with ‘dilution’ of the surfactant due to interfacial area increases. These two different effects of surface-active material are illustrated and discussed and their influence on the critical capillary number for breakup is presented.

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