Ferrofluid flow phenomena

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (leaves 155-158).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.An investigation of ferrofluid experiments and analysis is presented in three parts: a characterization of ferrofluid properties, a study of ferrofluid flow in tubing and channel systems, and a study of ferrofluid free surface sheet flows. The characterization of ferrofluid samples is completed through analysis of magnetization curves measured with a vibrating sample magnetometer. Determination is made of the ferrofluid particle size range, saturation magnetization, low-field magnetic permeability, and magnetic volume fraction. The experimental results are well described by the Langevin theory of paramagnetism. A detailed discussion of the demagnetization factor within the ferrofluid sample is also included. Ferrofluid flow through circular tubing in a laminar regime is examined as a function of the applied magnetic field magnitude, direction, and frequency. Gradients within the applied magnetic field create a magnetic contribution to the pressure drop across a length of tubing. Experiments of ferrofluid flow through a rectangular channel with a free surface when driven by a rotating spatially uniform magnetic field exhibit an anti-symmetric flow profile across the channel width, with a net zero flow rate, consistent with theoretical work of previous research. The first known investigation of ferrofluid free surface sheet flows resulting from a ferrofluid jet impacting a small circular plate is presented. Two distinct magnetic field orientations relative to the incident jet and resulting sheet are examined, producing markedly different results. A magnetic field oriented perpendicular to the jet flow is found to deform the jet cross-section from circular toward an elliptical shape thereby causing the sheet to also change from circular to elliptical, but with the long axis of the sheet oriented perpendicularly to the long axis of the jet cross-section. In the case of a magnetic field applied everywhere perpendicular to the sheet flow a significant decrease in sheet radius is observed. The cause of the decrease in sheet radius is a magnetic field induced decrease in ferrofluid pressure as well as a magnetic field enhanced convective Kelvin-Helmholtz instability. A thorough theoretical development describes the observed phenomena.by Thomas A. Franklin.S.M

Influence of Magnetic Nanoparticles and Magnetic Stress on an Ionic Liquid Electrospray Source

Two electrospray sources were developed to operate on an ionic liquid ferrofluid; one source was a pressure‑fed capillary electrospray source and the other was a novel electrospray source which used a magnetically‑induced instability to produce a peak from which an electric field could extract electrospray. Multiple characteristics of electrospray operation were examined for both sources using faraday plates/cups, a quartz crystal microbalance, a retarding potential analyzer, and a time-of-flight mass spectrometer. The ILFF electrosprays for a capillary source were shown to operate in a mixed ion/droplet regime. The mass flow of the electrospray beam was primarily transported by larger particles (potential droplets) within it. The magnetic nanoparticles increased the required flowrate and extraction potential of the source, as well as the emission current at a given flowrate. The nanoparticles also influenced the beam divergence and energy of an electrospray, increasing and decreasing each respectively with higher concentrations of NPs. The magnetic field had significant influence on the required flowrate of the electrospray, as it reduced the minimum stable flowrate by upwards of 16 percent. It also was shown to decreased the emission current of ILFF electrosprays for a given flowrate, while concurrently increasing the beam energy of particles in the electrospray. Other effects of magnetic field on electrospray characteristics were either inconclusive or insignificant

Microfluidics and Nanofluidics Handbook

The Microfluidics and Nanofluidics Handbook: Two-Volume Set comprehensively captures the cross-disciplinary breadth of the fields of micro- and nanofluidics, which encompass the biological sciences, chemistry, physics and engineering applications. To fill the knowledge gap between engineering and the basic sciences, the editors pulled together key individuals, well known in their respective areas, to author chapters that help graduate students, scientists, and practicing engineers understand the overall area of microfluidics and nanofluidics. Topics covered include Finite Volume Method for Numerical Simulation Lattice Boltzmann Method and Its Applications in Microfluidics Microparticle and Nanoparticle Manipulation Methane Solubility Enhancement in Water Confined to Nanoscale Pores Volume Two: Fabrication, Implementation, and Applications focuses on topics related to experimental and numerical methods. It also covers fabrication and applications in a variety of areas, from aerospace to biological systems. Reflecting the inherent nature of microfluidics and nanofluidics, the book includes as much interdisciplinary knowledge as possible. It provides the fundamental science background for newcomers and advanced techniques and concepts for experienced researchers and professionals

Radiative and magnetohydrodynamics flow of third grade viscoelastic fluid past an isothermal inverted cone in the presence of heat generation/absorption

A mathematical analysis is presented to investigate the nonlinear, isothermal, steady-state, free convection boundary layer flow of an incompressible third grade viscoelastic fluid past an isothermal inverted cone in the presence of magnetohydrodynamic, thermal radiation and heat generation/absorption. The transformed conservation equations for linear momentum, heat and mass are solved numerically subject to the realistic boundary conditions using the second-order accurate implicit finite-difference Keller Box Method. The numerical code is validated with previous studies. Detailed interpretation of the computations is included. The present simulations are of interest in chemical engineering systems and solvent and low-density polymer materials processing

Magnetically actuated micropumps

"Lab-On-a-Chip" (LOC) systems are intended to transpose complete laboratory instrumentations on the few square centimetres of a single microfluidic chip. With such devices the objective is to minimize the time and cost associated with routine biological analysis while improving reproducibility. At the heart of these systems, a fluid delivery unit controls and transfers tiny quantities of liquids enabling the biological assays. This explains the need for robust integrated micropumps as a precondition for the development of many LOC devices. In this context, we have developed a rapid prototyping method for the fabrication of microfluidic chips in plastic and glass materials. The microfabrication principle, which is based on the powder blasting microstructuring process, was used to build devices in either polymethylmethacrylate (PMMA) or borosilicate glass. Various types of micropumps have been developed which were all based on external magnetic actuation. The use of ferrofluids (or magnetic liquids) has been the subject of the first part of the research. A piston pump using a ferrofluid plug moved by an external magnet has been studied. The integration of a rare-earth material (NdFeB) in a flexible polydimethylsiloxane (PDMS) membrane, in the form of a powder or as a classical permanent magnet, has then been proposed. An external electromagnet was used to actuate the magnet-containing diaphragm of a reciprocating micropump. Different types of valves, which constitute the critical element in reciprocating micropumps, have also been investigated. We have studied silicone membrane valves, nozzle-diffuser elements and ball valves. While nozzle-diffuser elements present the simplest valving solution from a manufacturing point of view, ball valves have been proposed as a very promising alternative due to their high efficiency. Together with the detailed characterization of the prototypes, we have proposed analytical models that predict the hydrodynamic behaviour of the micropumps. The performances of our micropumps indicate that magnetic actuation is well adapted for LOC microsystems. While we have demonstrated that our proposed microfabrication technique is an excellent rapid prototyping method for disposable plastic devices, our glass micropumps present a competitive low-cost alternative satisfying criteria of biocompatibility and high temperature (130 °C) resistance

Magnetic field directed self-assembly of gold Pickering emulsion for preparing patterned film.

Patterning plays a vital in role in sensor-based devices like surface-enhanced Raman spectroscopy (SERS), surface-enhanced infrared absorption (SEIRA), radio frequency (RF) antennas and many others. The linear array spacing and width of gold strips has been shown to increase the local intensity through near-field coupling with diffracted electromagnetic waves. This rise in local charge boosts vibrational energies of molecules in close-surface contact or proximity, resulting in increased IR absorption. The strip-like or any other types of patterns are efficiently achieved through top-down nanofabrication processes like atomic-force-deposition, nanoimprinting, UV-Lithography etc., which involve high capital cost, complex processing and occasionally low throughput. This research was therefore undertaken with the aim of reducing the process complexities and improving scalability, by applying a magnetic and spin coating directed self-assembly (MSCDS) to prepare optically sensitive dipole-dipole chain-like ordered arrays of the gold nanoparticle Pickering ferrofluid in polyvinyl alcohol (PVA) emulsion, in the form of a thin film on glass and silicon substrate. Previously-conducted MSCDS processes lacked the control over the dimensions of the prepared patterns. Here, the static magnetic field approach was taken to modify the MSCDS process to overcome the limitation of pattern dimension control, providing tuneability for optical applications. Quantitative image analysis of the patterned thin film allowed for the measurement of pattern geometrical dimension (chain length-CL, chain gap-CG and chain thickness-CT), which was then correlated with processing parameters such as magnetic field configurations (single, compound and concentric), spinning speeds and viscosities of Pickering emulsion. Upon optimization, spectroscopical characterisation was performed on prepared patterned thin film to demonstrate the capability of the modified MSDS process in enhancing the molecular detection at low concentrations. The UV-vis spectra of the patterns demonstrated the impact of CT and CG on the degree of gold-iron oxide nanoscale interactions leading to tuneability of absorption bands between 390-700nm. The coupling of the increased optical sensitivity through enhanced charge transfer dynamics with the mid-infra-red range grating order (CT+CG) resulted in an amplification in vibrational band excitation of molecular bonds. For example, SEIRA measurements of thin film patterns showed a vibrational signal enhancement in asymmetric vibration of -CH2 (2920cm-1) bonds of PVA by 40%, as CT increased by 178% from 1.2μm at probing 45 degree grazing angle. Furthermore, the magneto-optical SERS phenomenon - involving local polarization of gold nanoparticles through the neighbouring magnetised iron oxide nanoparticle in the presence of external magnetic field - was exploited to reveal the varying degree of enhancement in peaks related to Rhodamine 6G (R6G) coated on thin film nanostructure, which was dependent on magnetized CT/CG morphology; especially the C-C-C ring (671 cm-1), for which the Raman peak increased by 12,000% when magnetized by a 43mT field. In summary, the modified MSCDC process is cheap with an expandable throughput rate ( > 0.1 m2/h) and flexible designs, offering both nanoscale and microscale tuneability of pattern dimensions. Even with higher defectivity (~14%) in comparison to the nanoimprinting method, this method can potentially be used to create repetitive array-like structure. Furthermore, the use of iron oxide reduces the cost without sacrificing the optical performance and thus contributes to the optical tuneability of the thin film nanostructure, thereby making the entire product a potential absorbing antenna and microfluidics thin film for biomolecule detection

Magnetic Hybrid-Materials

Externally tunable properties allow for new applications of suspensions of micro- and nanoparticles in sensors and actuators in technical and medical applications. By means of easy to generate and control magnetic fields, fluids inside of matrices are studied. This monnograph delivers the latest insigths into multi-scale modelling, manufacturing and application of those magnetic hybrid materials

Analysis, Design and Fabrication of Micromixers, Volume II

Micromixers are an important component in micrototal analysis systems and lab-on-a-chip platforms which are widely used for sample preparation and analysis, drug delivery, and biological and chemical synthesis. The Special Issue "Analysis, Design and Fabrication of Micromixers II" published in Micromachines covers new mechanisms, numerical and/or experimental mixing analysis, design, and fabrication of various micromixers. This reprint includes an editorial, two review papers, and eleven research papers reporting on five active and six passive micromixers. Three of the active micromixers have electrokinetic driving force, but the other two are activated by mechanical mechanism and acoustic streaming. Three studies employs non-Newtonian working fluids, one of which deals with nano-non-Newtonian fluids. Most of the cases investigated micromixer design

Magnetic Hybrid-Materials

Externally tunable properties allow for new applications of suspensions of micro- and nanoparticles in sensors and actuators in technical and medical applications. By means of easy to generate and control magnetic fields, fluids inside of matrices are studied. This monnograph delivers the latest insigths into multi-scale modelling, manufacturing and application of those magnetic hybrid materials