Dissertations / Theses on the topic 'Microfluidics. Fluidic devices. Mixing'

Thesis (Ph. D.)--Ohio State University, 2003.
Title from first page of PDF file. Document formatted into pages; contains xiv, 212 p.; also includes graphics. Includes bibliographical references (p. 195-202).

Microfluidics miniaturizes many benchtop processes and provides advantages of low cost, reduced reagent usage, process integration, and faster analyses. Microfluidic devices have been fabricated from a wide variety of materials and methods for many applications. This dissertation describes four such examples, each employing different features and fabrication methods or materials in order to achieve their respective goals. In the first example of microfluidic applications in this dissertation, thermoplastics are hot embossed to form t-shaped channels for microchip electrophoresis. These devices are used to separate six preterm birth (PTB) biomarkers and establish a limit of detection for each. The next chapter describes 3D printed devices with reversed-phase monoliths for solid-phase extraction and on-chip fluorescent labeling of PTB biomarkers. I demonstrate the optimization of the monolith and selective retention of nine PTB biomarkers, the first microchip study to perform an analysis on this entire panel. The third project describes the iterative design and fabrication of glass/polydimethylsiloxane (PDMS) devices with gold and nickel electrodes for the self-assembly of DNA nanotubes for site-selective placement of nanowires. Simple flow channels and “patch electrode” devices were successfully used, and DNA seeding was achieved on gold electrodes. Finally, a 3D printed device for cancer drug screening was developed as a replacement for one previously fabricated in PDMS. Devices of increasing complexity were fabricated, and those tested found to give good control over fluid flow for multiple inlets and valves. Although the applications and methods of these projects are varied, the work in this dissertation demonstrates the potential of microfluidics in several fields, particularly for diagnostics, therapeutics, and nanoelectronics. Furthermore, it demonstrates the importance of applying appropriate tools to each problem to gain specific advantages. Each of the described devices has the potential for increased complexity and integration, which further emphasizes the advantages of miniaturized analyses and the potential for microfluidics for analytical testing in years to come.

This thesis, written by Ingrid Öberg Månsson at KTH Royal Institute of Technology and entitled “Electroanalytical devices with fluidic control using textile materials and methods”, presents experimental studies on the development of textile based electronic devices and biosensors. One of the reasons why this is of interest is the growing demand for integrated smart products for wearable health monitoring or energy harvesting. To enable such products, new interdisciplinary fields arise combining traditional textile technology and electronics. Textile based devices have garnered much interest in recent years due to their innate ability to incorporate function directly into, for example, clothing or bandages by textile processes such as weaving, knitting or stitching. However, many modifications of yarns required for such applications are not available on an industrial scale. The major objective of this work has been to study how to achieve the performance necessary to create electronic textile devices by either coating yarns with conductive material or using commercially available conductive yarns that are functionalized to create sensing elements. Further, liquid transport within textile materials has been studied to be able to control the contact area between electrolyte and electrodes in electrochemical devices such as sensors and transistors. Yarns with specially designed cross-sections, traditionally used in sportswear to wick sweat away from the body and enhance evaporation, was used to transport electrolyte liquids to come in contact with yarn electrodes. The defined area of the junction where the fluidic yarn meets the conductive yarn was shown to increase stability of the measurements and the reproducibility between devices. The results presented in the two publications of this thesis as well as additional results presented in the thesis itself show the promising potential of using textile materials to integrate electronic and electrochemical functionality in our everyday life. This is shown by using basic textile materials and processing techniques to fabricate complex devices for various application areas such as sensors and diagnostics as well as electrical and energy harvesting components.
Denna avhandling, skriven av Ingrid Öberg Månsson vid Kungliga Tekniska Högskolan och titulerad ”Elektroanalytiska sensorer med vätskekontroll integrerad genom användande av textila material och metoder”, presenterar experimentella studier inom utvecklingen av textilbaserade elektroniska komponenter och biosensorer. Detta är av intresse på grund av den ökade efterfrågan på integrerade smarta produkter som till exempel bärbara sensorer för hälsoövervakning eller för att samla upp och konvertera energi till elektricitet. För att möjliggöra denna typ av produkter föds nya interdisciplinära fält där traditionell textilteknologi och elektronik möts. Textilbaserade enheter har väckt stort intresse under de senaste åren på grund av den naturliga förmågan att integrera funktion i till exempel kläder eller förband genom textila tillverkningsprocesser som väveri, stickning eller sömnad. Många modifikationer hos garner som krävs för att möjliggöra sådana tillämpningar är dock inte tillgängliga i större skala. Därför har det huvudsakliga syftet med denna studie varit att undersöka hur man kan uppnå den prestanda som krävs för att tillverka elektroniska textila komponenter, antingen genom att belägga garner med elektroniskt ledande material eller genom att använda kommersiellt tillgängliga ledande garner som sedan modifieras kemiskt för att skapa sensorer. Utöver detta har vätsketransport inom textila material studerats för att kunna styra och kontrollera kontaktytan mellan elektrolyt och elektroder i elektrokemiska enheter så som sensorer och transistorer. Garner med speciella tvärsnitt, som traditionellt använts i sportkläder för att transportera svett bort från kroppen och underlätta avdunstning, har använts för att transportera elektrolytvätska till elektroder av garn. Den definierade kontaktytan där det vätsketransporterade garnet korsar elektrodgarnet har visats öka stabiliteten av mätningen och reproducerbarheten mellan mätenheter. Resultaten som presenteras i de två artiklar som denna avhandling bygger på samt i avhandlingen själv visar på lovande potential för användandet av textila material för att integrera elektronisk och elektrokemisk funktionalitet i våra vardagsliv. Detta har uppnåtts genom att använda grundläggande textila material och tillverkningsprocesser för att tillverka komplexa enheter för olika tillämpningsområden så som sensorer för diagnostik samt elektroniska komponenter.

QC 2020-08-21

Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2007.
Committee Chair: Hesketh, Peter J.; Committee Member: Allen, Mark G.; Committee Member: Degertekin, F. Levent; Committee Member: Frazier, Bruno A.; Committee Member: Graham, Samuel.

by Chow Wing Yin, Winnie.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2004.
Includes bibliographical references (leaves 74-78).
Abstracts in English and Chinese.
ABSTRACT --- p.i
摘要 --- p.ii
ACKNOWLEDGEMENTS --- p.iii
TABLE OF CONTENTS --- p.iv
LIST OF FIGURES --- p.vi
LIST OF TABLES --- p.viii
Chapter 1 --- INTRODUCTION --- p.1
Chapter 1.1 --- Digital Microfluidics --- p.1
Chapter 1.2 --- Soft Lithography of Polymer --- p.2
Chapter 2 --- ELECTROCAPILLARY-BASED MICROACTUATION --- p.5
Chapter 2.1 --- Surface Tension in Microscale --- p.5
Chapter 2.2 --- thermocapillary-based microactuation --- p.6
Chapter 2.3 --- electrocapillary-based microactuation --- p.6
Chapter 2.3.1 --- Continuous Electrowetting (CEW) --- p.7
Chapter 2.3.2 --- Electrowetting (EW) --- p.8
Chapter 2.3.3 --- Electrowetting-On-Dielectric (EWOD) --- p.11
Chapter 3 --- SOFT LITHOGRAPHY --- p.14
Chapter 3.1 --- Rapid Prototyping --- p.15
Chapter 3.2 --- Replica Molding --- p.16
Chapter 3.2.1 --- Pouring Method --- p.17
Chapter 3.2.2 --- Sandwich Molding Method --- p.17
Chapter 3.2.3 --- Spin On Method --- p.18
Chapter 3.3 --- Sealing --- p.20
Chapter 3.3.1 --- Reversible Sealing --- p.20
Chapter 3.3.2 --- Irreversible Sealing --- p.20
Chapter 3.4 --- Multilayer Fabrication --- p.21
Chapter 4 --- METAL DEPOSITION --- p.22
Chapter 4.1 --- Gold Deposition by Sputtering Method --- p.22
Chapter 4.1.1 --- Gold Deposition on PMMA --- p.22
Chapter 4.1.2 --- Gold Deposition on PDMS --- p.23
Chapter 4.2 --- ITO Deposition by Sputtering Method --- p.26
Chapter 4.2.1 --- Image Patterning of ITO --- p.27
Chapter 5 --- POLYMER-BASED SUBSTRATES BONDING USING PDMS --- p.29
Chapter 5.1 --- Design of Microfluidic System --- p.29
Chapter 5.1.1 --- PDMS --- p.29
Chapter 5.1.2 --- Design of the Vortex Micropump --- p.30
Chapter 5.2 --- Fabrication of Microfluidic System --- p.31
Chapter 5.2.1 --- Micro Impeller Fabrication Process --- p.31
Chapter 5.2.2 --- Micro Patterning of PMMA by Hot Embossing Technique --- p.32
Chapter 5.2.3 --- Assembly of Micropump by PDMS Bonding Process --- p.34
Chapter 5.3 --- Experimental Results --- p.36
Chapter 5.3.1 --- Tensile Bonding Test --- p.36
Chapter 5.3.2 --- Leakage Test --- p.38
Chapter 6 --- DIGITAL MICROFLUIDICS IN MICROCHANNEL --- p.39
Chapter 6.1 --- Digital Microfluidics --- p.39
Chapter 6.2 --- Design of the MicroChannel --- p.39
Chapter 6.3 --- Materials of the MicroChannel --- p.42
Chapter 6.3.1 --- Substrate --- p.42
Chapter 6.3.2 --- Adhesion Layer --- p.42
Chapter 6.3.3 --- Electrode --- p.43
Chapter 6.3.4 --- Dielectric Layer --- p.43
Chapter 6.4 --- Fabrication of the MicroChannel --- p.44
Chapter 7 --- EXPERIMENTAL RESULTS --- p.46
Chapter 7.1 --- ewod on pdms layer --- p.46
Chapter 7.2 --- PDMS Parallel Plate Channel --- p.48
Chapter 7.2.1 --- Contact Angle --- p.49
Chapter 7.3 --- Parylene C Parallel Plate Channel --- p.52
Chapter 7.4 --- Sealed pdms MicroChannel --- p.54
Chapter 7.5 --- Driving Pressure --- p.55
Chapter 7.6 --- microchannel in the vertical position --- p.57
Chapter 8 --- FUTURE WORK --- p.60
Chapter 8.1. --- Digital Microfluidic Circuit Design --- p.60
Chapter 8.1.1. --- Electrodes Design --- p.61
Chapter 8.2. --- Fabrication Process --- p.63
Chapter 9 --- SUMMARY --- p.64
APPENDIX A --- p.67
BIBLIOGRAPHY --- p.74

Micro-fluid mixing is an important aspect of many of the various micro-fluidic systems used in biochemical production, biomedical industries, micro-energy systems and some electronic devices. Typically, because of size constraints and laminar flow conditions, different fluids may only have the opportunity to mix by diffusion, which is extremely rate limited. Therefore, active or highly effective passive mixing techniques are often required. In this study, two pulsed injectors are used to actively enhance mixing in a high aspect ratio microchannel (125 ��m deep and 1 mm wide). The main channel has two adjacent flowing streams with 100% dye and 0% dye concentrations, respectively. Two injectors (125 ��m deep and 250 ��m wide) are located on separate sides of the channel, with one downstream 2 mm (equivalent to two main channel widths or eight injector widths) from the other. This results in an asymmetric mixing as the flow proceeds downstream. A dye solution is used to map local mixing throughout the channel by measuring concentration variations as a function of both space and time. The primary flow rates are varied from 0.01 to 0.20 ml/min (Reynolds numbers of 0.3 to 26.6), the injector flow rate ratios are varied from 0.125 to 2, and the pulsing frequencies are varied from 5 to 15 Hz. Images of the concentration variations within the channel are used to quantify mixing by calibrating the intensity of the image with the concentration of the dye solution. The degree of mixing (DoM) is used as a measure of quality and is defined based on the integration across the channel of the difference between the local concentration and the 50% concentration values. DoM is normalized by the 50% concentration value and subtracted from one to yield a parameter that varies from 0 (no mixing) to 1 (perfect mixing). It is shown that there is a high degree of repeatability of concentration distribution as a function of phase of the pulsing cycle. A mixing map is constructed over the range of variables tested which indicates an optimum set of flow and pulsing conditions needed to achieve maximum mixing in the main channel flow. The flow rate ratio between the injectors and main channel is found to be the most influential parameter on overall mixing. The highest DoM in the main channel was found to be 0.89. It is also noticed that improved mixing can occur at very low flow ratios under a unique set of primary flow and low frequency pulsing conditions. In general, there is an inverse relationship between primary flow rate and pulsing frequency to achieve better overall mixing.
Graduation date: 2003

The physical mechanism responsible for droplet manipulation in electrowetting on dielectric (EWOD) devices is not yet fully understood. This investigation will examine the role of capillary forces on droplet manipulation to further the physical understanding of these devices. An analytical model for the capillary force acting on a confined droplet at equilibrium is developed here. Model predictions were validated using optical measurements of the droplet interface in the vertical plane. It was found that the capillary force and interface shape predicted by the equilibrium model were over an order of magnitude more accurate than predictions from the model commonly used in EWOD investigations. The equilibrium model was adapted to droplets with arbitrary shapes to predict droplet dynamics in EWOD devices. It was found that droplet motion could be described using the driving capillary force and frictional forces from wall shear, the contact line, and contact angle hysteresis. Comparison with experimental data shows that this model accurately predicts the effects of applied voltage and droplet aspect ratio on the transient position and velocity of droplets. This model can be used to design EWOD devices and predict the simultaneous manipulation of droplets required to meet the high throughput demands of practical applications. A robust system for droplet monitoring must be automated before EWOD devices can be used reliably in practical applications. Although capacitance measurements have been used to automate droplet detection in EWOD devices, manual optical measurements are generally used to monitor droplet mixing. This may not be possible in high throughput applications with multiple droplets and limited optical access. Here, capacitance measurements are shown to be an accurate and repeatable means of monitoring droplet composition and real time mixing. Experiments were performed with this technique to show that mixing efficiency is better characterized by the number of translations required for full mixing, not mixing time.

Thesis (Ph. D.)--University of Alberta, 2010.
Title from pdf file main screen (viewed on July 8, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Department of Physics, University of Alberta. Includes bibliographical references.

A two-dimensional model was developed to predict concentration profiles from passive, laminar mixing of concentration layers formed in a fractal-like merging channel network. Both flat and parabolic velocity profiles were used in the model. A physical experiment was used to confirm the results of the model. Concentration profiles were acquired in the channels using laser induced fluorescence. The degree of mixing was defined and used to quantify the mixing in the test section. Although the results of the experiment follow the trend predicted by the two-dimensional model, the model under predicts the results of the experiment. A three-dimensional CFD model of the flow field in the channel network was used to explain the discrepancies between the two-dimensional model and the experiment. For the channel network considered, the degree of mixing is a function of Peclet number. The effect of geometry on the degree of mixing is investigated using the two-dimensional model by varying the flow length, the width of the inlet channels, and the number of branching levels. A non-dimensional parameter is defined and used to predict an optimum number of branching levels to maximize mixing for a fixed inlet channel width, total length, and channel depth.
Graduation date: 2003

Indiana University-Purdue University Indianapolis (IUPUI)
The purpose of this thesis is to use experimental methods to seek deeper understanding and better performance in the self-circulating self-regulating microfluidic gas generator initially developed in Dr. Zhu’s group, by changing the major features and dimensions in the reaction channel of the device. In order to effectively conduct experiments described above, a microfabrication method that is capable of making new microfluidic devices with low cost, short time period, as well as relatively high accuracy was needed first. Developing such a fabrication method is the major part of this thesis. We initially used patterned polymer films and glass slide, and bonded them together by sequentially aligning and stacking them into a microfluidic device with patterned double-sided tapes. Later we developed a more advanced microfabrication method that used only patterned polystyrene (PS) films. The patterned PS films were obtained from a digital cutter and they were bonded into a microfluidic device by thermopress bonding method that required no heterogeneous bonding agents. This new method did not need manual assembly which greatly improved its precision (~ 100 µm), and it used only PS as device material that has favorable surface wetting property for microfluidics applications. In order to find the optimized microfluidic channel design to improve gas generating performance, we've designed and fabricated microfluidic devices with different channel dimensions using the PS fabrication method. Based on the gas generation testing results of those devices, we were able to come up with the optimal dimensions for the reaction channel that had the best gas generation performance. To obtain a more fundamental understanding about the working mechanism of our device and its bubble dynamics, we have conducted ultrafast X-ray imaging test at Advanced Photon Source (APS), Argonne National Laboratory. High speed (100 KHz) phase contrast images were captured that allowed us to observe directly inside the reaction channel on the cross section view during the self-circulating catalytic reaction. The images provided us with lots of insightful information that in turn helped the dimensional improvement for the microchannel design. The 100 KHz high speed images also gave us useful information about the dynamics of bubble development on a catalyst bed, such as growth and merging of the bubbles.

Indiana University-Purdue University Indianapolis (IUPUI)
In this study, a novel model for manipulating cancer blood cells based on multi-stage micro channels under varied low field concepts is proposed. Steering Device approach was followed to manipulate the cancer cells based on their various differential potentials across their membranes. The proposed approach considers the size and the surface potential as well as the iso electronic structure of the cells. These research objectives emphasize the separation of the cells in the blood stream, and differentiates various blood cells and tumors for further analysis within the microfluidic channels. The dimensions of the channel sets the required electric field for manipulating the cancer cells within the channels using low electrode voltage function. The outcomes of this research may introduce a new diagnostic approach of finding the minimum residual disease (MRD) scans, early detection and analysis scans. This thesis provides a mathematical model, detailing the theory of the cell sorting device, manipulating the blood cancer cells and design of the device structure are also detailed, leading to the optimum research parameters and process. A Computer Aided Design (CAD) was used to model the multi-cell sorting lab-on-chip device, details of hardware and software were used in the simulation of the device various stages. Reverse engineering to configure the potentials for sorting mechanism needs is discussed. The thesis work also presents a comparative study of this sorting mechanism and the other commercially available devices. The practical model of the proposed research is laid out for future consideration.