This paper presents results of the performance of microfluidic amplifiers of the jet deflection type with hydraulic diameter up to 41 µm, built in silicon using a mixture of wet and dry etching. The amplifier diverts a supply flow into one of two outputs using two smaller control flows. Reversing the control flow, the output flows are switched symmetrically. The output ports were always open to atmosphere, with positive manometric pressure being applied to cause the supply and control flows. Both flow rate and pressure measurements were taken to fully characterize the operation. The devices showed symmetrical flow splitting behavior without any control flows. Increasing one of the control flow, while keeping the other control input open to atmosphere, caused the flow out of the opposing output to increase proportionally with increasing flow gains. The flow gain remained in linear range with control flows up to 40×l0-9 Kg/s. Above that, saturation and output loading effects degraded the flow gain. For supply flows larger than 500×l0-9 kg/s, the average flow gain started to decrease. This is believed to be caused by the onset of turbulence and possibly by the occurrence of normal and oblique shocks in the interaction region. A better understanding of these limiting processes is needed to obtain optimized amplifier designs with larger flow gains.

This work aimed the conception, manufacturing and testing of planar miniaturized structures useful for mixing. These structures were designed to manage heavily contaminated liquid samples, i.e. particulate material, and/or to mix flows even if flow rate ratio is 1:10. The structures were manufactured in acrylics, which lower the cost without compromising the good chemical resistance. A good performance can be achieved on flow rates among 30–60 ml/min and continuous flow. Another possible use for these devices is droplet formation.

This work presents the simulation results of the fluid flow behavior inside a preconcentrator microstructure. The preconcentrator was implemented in silicon using reactive ion etching, SF6 based, to define the channels and anodic bonding between silicon and borosilicate glass for sealing. The preconcentrator design takes in account the enhancement of surface to area ratio, by dividing the flow until it reaches 50 um channels. The internal flow was analyzed using the commercial package ANSYS/FLOTRAN. Vortex formation was not observed under the simulation conditions and resolution, for water flow of 100 μl/min. The flow is essentially laminar and velocity changes (variations) can be observed, that can influence the residence time of the species inside the microstructure and, consequently, the diffusion/adsorption mechanisms.

Spray production and its miniaturization are common need and goal in Chemical Engineering and Chemical fields. This work aims the production of miniaturized low cost spray injection systems using planar and three-dimensional microchannels, both 73 cm long and 100 μm diameter, and acrylic as substrate. Tests and simulation used fluid flow rates up to 10 standard mL/min, for gaseous samples, and up to 1 mL/min to liquid ones; tracers and filming were used to understanding fluid behavior. Simulations and experimental results showed good agreement: planar channels seem to be useful for mixing two liquids whereas three-dimensional channels produce small droplets useful for sample pretreatment in miniaturized impactors.

The aim of this work was to simulate, produce and tests a small-lab that possesses an array of miniaturized 3D structures with four different unit operations. These structures showed to be useful for particle removal and pre-concentration in sample pre-treatment in Chemical analysis or mixing and spray formation in Chemical Engineering synthesis. The device proposed showed to be a versatile and low-cost system that can be built using conventional tools.

Spray production and its miniaturization are common need and goal in Chemical Engineering and Chemical fields.This work aims the production of miniaturized low cost spray injection systems using planar and three-dimensional microchannels, both 73 cm long and 100 μm diameter, and acrylic as substrate.Tests and simulation used fluid flow rates up to 10 standard mL/min, for gaseous samples, and up to 1 mL/min to liquid ones; tracers and filming were used to understanding fluid behavior.Simulations and experimental results showed good agreement: planar channels seem to be useful for mixing two liquids whereas three-dimensional channels produce small droplets useful for sample pretreatment in miniaturized impactors.

Simulation and experimental measurements were used aiming at better understanding flow behavior in planar and three-dimensional microchannels used for separation or preconcentration.Two different microchannels configurations were designed, manufactured in acrylic and the surface was modified to adsorb volatile organic compounds (VOCs).Both channels configuration are 73 cm long, 100 µm wide and 40 µm deep.Simulation was carried out in COMSOL (FEMLAB) 3.2 ® and COSMOS flow 5.0 ® programs, tracer visualization and quartz crystal microbalance data were evaluated according to chromatographic concepts.Due to the higher axial velocity, planar microchannels are more adequate for preconcentration whereas three-dimensional ones show a good performance in the separation process.

The aim of this work was the production of a large surface area of hexamethyldisilazane (HMDS) plasma-deposited thin films and their applicability in a miniaturized structure useful for preliminary analysis of organic mixtures. The HMDS plasma films were produced with different surface areas and morphologies, and all films adsorbed polar and non-polar organic compounds. A low cost miniaturized structure was manufactured in glass using a Milling cutter and covered with HMDS plasma films. Good agreement was observed between simulation and experimental results on those microstructures. The observed different performance between pure and mixtures of organic compound samples suggests that the proposed system is a simple setup that could be useful for rough analysis of a fuel.

The aim of this work is the production of a simple and compactable device able to remove hydrocarbons from a gaseous sample. The device is composed of a microstructure, inlet/outlet, heating and detection systems. The microstructure (microreactor) corresponds to a manifold formed by an array of 192 three-dimensional microchannels, 40μm wide and 8mm long each. Microchannels surface was modified by electroless plating copper deposition in order to promote catalysis. The structure can be heated up to 300°C in a few seconds. The flow mechanisms in the structure and the heating properties were simulated using FEMLAB 3.2b and COSMOS® 5.0 packages, respectively. The microchannels were exposed to volatile organic compounds during catalysis. An inexpensive tin oxide sensor and correspondent electronic coupled to computer storage data provided detection. Catalysis occurred and could remove at least 10μg of n-hexane in a single batch, but not 2-propanol. This simple miniaturized device is compact, low-cost and can be used not only for sample pretreatment in microanalysis but also in synthesis of new chemical compounds.

The aim of this work is the production and preliminary characterization of adsorbent new materials useful for sensor development. A new plasma chamber was simulated and designed in order to obtain multiple layers and/or composites in a single step. Plasma deposited organic fluorocompound and hexamethyldisilazane (HMDS) thin films were produced and tested as adsorbent layers. Chemical characterization used ellipsometry, Raman, infrared and X-ray photoelectron spectroscopy. Hydrophobic and oleophobic character were determined by contact angle measurements. Adsorption characteristics were evaluated using quartz crystal microbalance. Not only HMDS but also the fluorocompound can polymerize but intermixing and a double layer are only obtained in very narrow conditions. The films are adsorbent and mildly hydrophobic. Films deposited on a microchromatographic column can be used on sample pretreatment to remove and/or preconcentrate volatile organic compounds. Therefore, with this approach it is possible to obtain films with different monomers on double layer or composites, with organic/inorganic materials or particles and use them on sample pretreatment for chemical analysis.

Adsorbent materials and composites are quite useful for sensor development. Therefore, the aim of this work is the surface modification of particulates and/or composite formation. The material was produced by plasma polymerization of HMDS (hexamethyldisilazane) in a single step. SEM analysis shows good surface coverage of particulates with a plasma polymerized film formed by several clusters that might increase adsorption. Particles (starch, 5μm) recovered with HMDS films show good properties for retention of medium-size organic molecules, such as dye. Thin films formed by a mixture of particles and plasma polymerized thin film HMDS species were obtained in a single step and can be used for retention of organic compounds, in liquid or gaseous phase.

Ethanol obtained from sugar cane ( Saccharum) has been used as automotive fuel in Brazil for decades. In spite of its undoubted success, several dishonest dealers sell fake mixtures that can cause serious damages to engines. Regular water (without any treatment) is the main additive used to adulterate the ethanol fuel sold at gas stations throughout Brazil. In a previous work we have demonstrated that interdigitated capacitive microsensors were able to distinguish different types of fuels based on the difference of their dielectric properties. The present work is focused on the use of improved versions of our microsensors for testing the quality of ethanol automotive fuel. This new generation of microsensors was designed to measure not only the capacitance; they can also promote some electrochemical reactions and are able to detect some physicochemical modifications that occur in the presence of alcohol, water and other solvents. Several samples have been prepared using conventional microfabrication techniques. Substrates of alumina and glass were utilized, while interdigitated structures were made of electroplated nickel or silver or nickel covered with gold. The interdigitated electrodes form hundreds of capacitors in parallel connection. The width of the grown electrodes is around 50µm, and the gap between electrodes is usually from 50µm to 100µm wide. The thickness of the interdigitated electrodes varies from 5µm to 30µm, depending on the metal used. Several characterizations were performed using an impedance analyzer, and the sensors were able to distinguish several types of adulterations.

In this work silica nanoparticles were incorporated in a polymeric matrix (fibers) aiming at the production of new composite materials that can be useful for the development of nanomaterials and/or microanalysis systems. Polyethyleneoxide and Ludox TM-50 were used as phases for electrospinning. Due to the high amount of effective charge present in the solutions, a new setup for electrospinning was devised by adding another electrode to a conventional deposition system. The presence of this electrode was investigated numerically using electrostatic application mode of the COMSOL Multiphysics 3.2b package. The simple model developed to explain the nanoparticle behavior for the used electrospinning setup showed good agreement with the experimental results and can be useful for simulations in the production of similar composites. Fibers with a high amount of particles were obtained using this third electrode biasing the flow in a preferred direction. Infrared spectra, EDX and SEM microscopy analysis show nanoparticle incorporation in the fibers. (c) 2007 Elsevier Ltd. All rights reserved.

The aim of this work was the development of miniaturized structures useful for retention and/or selection of particles and viscous substances from a liquid flow. The proposed low costs structures are similar to macroscopic wastewater treatment systems, named baffles, and allow disassemble. They were simulated using FEMLAB 3.2b package and manufactured in acrylic with conventional tools. Tests for retention or selection of particles in water or air and viscous fluids in water were carried out. Either in air or water particles with 50μm diameter will be retained but not with 13μm diameter. In aqueous flow, it is also possible the retention of viscous samples, such as silicone 350 cSt. The simulated results showed good agreement with experimental measurements. These miniaturized structures can be useful in sample pretreatment for chemical analysis and microorganism manipulation.

The influence of the presence of constrictions in microchannels was investigated in this work, numerically and experimentally, aiming at to obtain preconcentrator microstructures for non-polar compounds that can be present as a contaminant in the air. The flow behavior inside the microstructures was analyzed using the ANSYS FLOTRAN 8.1 and EVOLVER 2.14 simulations packages. The experimental tests for evaluation of preconcentration characteristics were performed using gas mixtures with n-hexane (C6H14) inserted in a microchannel with a length of 30cm, width of 100μm and depth of 30μm. The microchannels were defined using RIE plasma etching and sealed with glass. Preconcentration was effectively observed and it was also demonstrated that the constrictions may favor the occurrence of capillary effects, as compared to adsorption effects, defining the dynamical behavior of the preconcentrator microstructure as a function of geometric and flow conditions. So far, these microstructures can be useful for the preconcentration process at high-contaminated environments, in which the human interference is not safe or small devices with high portability are required.

Transparent and planar meso-scale fluidic structures with no movable parts, based on feedback microfluidic oscillators, were manufactured in acrylic (using a computer numerically controlled milling machine) and sealed using thermo-compressive bonding. Internal flow images for the operation with water were analyzed considering supply flows in the range of 60 ml/min to 600 ml/min. Tracers with different viscosities were injected (continuously or in a pulsed way) to improve contrast. Depending on the constriction dimensions at the output of the feedback arms, these structures can present different behaviors associated with momentum interaction, and can be used for different applications. Smaller constrictions lead to structures that oscillate in any flow regime (1000<Re<10,000) while larger ones avoid oscillation but favor retention of fluid inside the feedback arms.

Microfluidic oscillators were obtained from wall attachment microfluidic amplifiers using a feedback loop from the outputs to the control inputs. These devices can be used as flow meters when the oscillation frequency is proportional to the volumetric flow rate in subsonic and moderately compressible conditions. They can also be used as actuators, for applications involving flow control and/or mixing. The devices, presenting critical dimensions of the order of 280 mum, were fabricated using SU-8 based epoxy photoresist and conventional photolithography. The article shows the results obtained in the experimental device tests with gases (nitrogen, argon, and carbon dioxide). The typical variation of the frequency with volumetric flow presents a range close to thousands of hertz. The oscillation frequencies were obtained using hot wire filament anemometers (in this case with a diameter of 12 mum). The experimental results indicate that the operation of the microfluidic oscillator was a direct function of the length of the feedback loops and of the velocity inside of the interaction region. (C) 2004 Elsevier Ltd. All rights reserved.

This article analyzes the performance of jet deflection microfluidic amplifiers implemented in silicon, using microchannels with a minimum hydraulic diameter of similar to40 mum. The implemented devices were characterized in terms of applications involving flow control and flow division. The implemented devices presented proportional or symmetrical behavior. For proportional control, high flow gains were obtained, similar to fluidic amplifiers with supply hydraulic diameters of hundreds of micrometers, being the average flow gain a function of supply flow. Numerical simulation analyses of the active part of the devices indicate the possibility of choked flow at the output of the supply nozzle.