Solution In Microchannel Research Articles

S054021 マイクロチャネルでの混合に対する高分子溶液の不安定流動の影響

In this study, we have investigated the mixing property of water and polymer solution in micro-channels. We have utilized T-shaped micro-channels which have contraction-expansion parts with five asymmetric rectangular block gates and observed the mixing procedure. Dyed water and a dilute aquaus solution of polyethylenoxide (PEO) of 100 ppm by weight were mixed in the tests. In the micro-channels, the polymer solution caused unstable vortexes before the rectangular gates and the instability of the flow grew at the later part of the contraction-expansion region. The unstable flow with the vortex due to the elastic property of the polymer solusion leaded the efficient mixing.

6-5 水の近赤外吸収特性を利用したマイクロ流路内水溶液の温度イメージング(セッション6:マイクロ物理センサ)

6-5 水の近赤外吸収特性を利用したマイクロ流路内水溶液の温度イメージング(セッション6:マイクロ物理センサ)

S056024 急縮小部を有するマイクロチャネル内の種々の水溶液の流動特性([S05602]複雑流体の流動現象(2))

S056024 急縮小部を有するマイクロチャネル内の種々の水溶液の流動特性([S05602]複雑流体の流動現象(2))

Temperature imaging of water in a microchannel using thermal sensitivity of near-infrared absorption

This paper presents a remote and preparation-free method of temperature imaging of aqueous solutions in microchannels of microfluidic chips. The principle of this method is based on the temperature dependency of the near-infrared (NIR) absorption band (ν(2) + ν(3) band) of water. Temperature images were constructed from absorbances in a narrow wavelength range including 1908 nm, the most sensitive to temperature in the band, measured by using an NIR camera and an optical narrow-bandpass filter. Calculation and calibration results demonstrated a linear relationship between the absorption coefficient and temperature with a temperature coefficient of 1.5 × 10(-2) K(-1) mm(-1). Temperature images of 50 μm thick water in a Y-shaped PDMS microchannel locally heated by a neighboring hot wire were obtained, in which thermal diffusion processes in the microchip were visualized. Temperature resolution was estimated to be approximately 0.2 K according to the temperature coefficient and noise level.

High shear rheology of shear banding fluids in microchannels

We characterize heterogeneous flows of a wormlike micelles solution in microchannels. Combining a pressure resistant microfabrication technology and a performant particle image velocimetry setup, we succeed in determining the nonlinear rheology of this fluid over 4 decades in shear rate and in particular more than 1 decade beyond the end of the stress plateau. We performed an independent measurement of the slip length with 1 μm resolution.

Thermophoresis of particles in aqueous solution in micro-channel

A theoretical analysis of micro motion of particles under the action of thermophoresis in aqueous electrolyte solution is presented in this paper. A two-dimensional, incompressible and laminar fluid flow model is proposed to simulate the fluid flow and particle motion trajectory in micro-channel. The effects of thermophoretic force and viscous force on the particle are calculated. The particle trajectories considering the effects of particle size, inlet flow velocity and temperature difference between bottom side and top side in micro-channel with a length of 2000 μm and a height of 500 μm are simulated. The effect of thermophoresis on separation motion of particles in micro-channel is analyzed. The results show that thermophoretic force increases with the increase of temperature gradient in micro-channel and particles with smaller diameter, smaller density and smaller gravity acceleration can pass the micro-channel more easily.

Desiccation kinetics of biopreservation solutions in microchannels

A microfluidic device was utilized to measure the viscosity gradients formed in carbohydrate solutions of biological significance during desiccation and skin formation. A complementary numerical model employed the free volume theory to predict the concentration-dependent diffusion coefficients and viscosity gradients in concentrated solutions. It was established that the glassy skin formation at the gas-liquid interface played a key role in water entrapment and the formation and persistence of very steep concentration and viscosity gradients in the desiccating solutions. The results of this study highlighted an important phenomenon that should be accounted for during isothermal drying of glass-forming solutions: solutions with high glass transition temperatures, inevitably, dry heterogeneously. In the final product, there are significant spatial variations in water and solute content affecting the storage stability.

Performance of microchannel reactor combined with combustor for methanol steam reforming

The microchannel reactor with combustor for methanol steam reforming was fabricated to produce hydrogen for onboard proton exchange membrane (PEM) fuel cell device. A commercial copper-containing catalyst (Cu/ZnO/Al 2O 3) and Pt/ZrO 2 were used as a catalyst for methanol steam reforming and combustion reaction, respectively. It was found that catalyst layer with zirconia sol solution in microchannel showed no crack on the surface of catalyst layer and an excellent adherence to stainless steel microchannel even after reaction. The temperature of combustor could be controlled between 200 and 300 °C depending on the methanol feed rate. The hydrogen flow of 3.9 l h −1 hydrogen was obtained with the reforming feed flow rate of 3.65 ml h −1 at 270 °C.

Photochemically Patterned Poly(methyl methacrylate) Surfaces Used in the Fabrication of Microanalytical Devices

We report here the photochemical surface modification of poly(methyl methacrylate), PMMA, microfluidic devices by UV light to yield pendant carboxylic acid surface moieties. Patterns of carboxylic acid sites can be formed from the micrometer to millimeter scale by exposure of PMMA through a contact mask, and the chemical patterns allow for further functionalization of PMMA microdevice surfaces to yield arrays or other structured architectures. Demonstrated here is the relationship between UV exposure time and PMMA surface wettability, topography, surface functional group density, and electroosmotic flow (EOF) of aqueous buffer solutions in microchannels made of PMMA. It is found that the water contact angle on PMMA surfaces decreases from 70 degrees to 24 degrees after exposure to UV light as the result of the formation of carboxylic acid sites. However, upon rinsing with 2-propanol, the water contact angle increases to approximately 80 degrees , and this increase is attributed to changes in surface roughness resulting from removal of low molecular weight PMMA formed from scission events. In addition, the surface roughness and surface coverage of carboxylic acid groups exhibit a characteristic trend with UV exposure time. Electroosmotic flow (EOF) in PMMA microchannels increases upon UV modification and is pH dependent. The possible photolysis mechanism for formation of carboxylic acid groups on PMMA surfaces under the conditions outlined in this work is discussed.

Effects of surface heterogeneity on flow circulation in electroosmotic flow in microchannels

The characteristics of electroosmotic flow in a cylindrical microchannel with non-uniform zeta potential distribution are investigated in this paper. Two-dimensional full Navier–Stokes equation is used to model the flow field and the pressure field. The numerical results show the distorted electroosmotic velocity profiles and various kinds of flow circulation resulting from the axial variation of the zeta potential. The influences of heterogeneous patterns of zeta potential on the velocity profile, the induced pressure distribution and the volumetric flow rate are discussed in this paper. This work shows that using either heterogeneous patterns of zeta potential or a combination of a heterogeneous zeta potential distribution and an applied pressure difference over the channel can generate local flow circulations and hence provide effective means to improve the mixing between different solutions in microchannels.

Proteinaceous bubble and nanoparticle flows in microchannels

Proteinaceous bubbles of 185 nm average diameter were synthesized by a sonochemical treatment of bovine serum albumin (BSA) in an aqueous solution and the nanoparticles (TiO2) solution was made by ultrasonic irradiation. To study the macroscopic flow behavior associated with the changes in the state of the microparticles, a flow test of these solutions in microchannels was done. Also, the size distributions of the proteinaceous bubbles in solution before and after the flow test were measured by a light scattering method. Test results show that the air-filled proteinaceous bubbles in solution adjust their size to reduce the shear stress encountered in the flow through the microchannel. On the other hand, the mass flow rate of the solution with nanoparticle suspensions becomes smaller than that of deionized water in a microchannel of dimension 100×100 μm2.

Electroviscous effects on pressure-driven flow of dilute electrolyte solutions in small microchannels

A fundamental understanding of the flow characteristics of electrolyte solutions in microchannels is critical to the design and control of microfluidic devices. Experimental studies have shown that the electroviscous effect is appreciable for a dilute solution in a small microchannel. However, the experimentally observed electroviscous effects cannot be predicted by the traditional theoretical model, which involves the use of the Boltzmann distribution for the ionic concentration field. It has been found that the Boltzmann distribution is not applicable to systems with dilute electrolyte solutions in small microchannels because it violates the ion number conservation condition. A new theoretical model is developed in this paper using the Nernst equation and the ion number conservation, instead of the Boltzmann distribution, to obtain the ionic concentration field. The ionic concentration field, electrical potential field, and flow field in small microchannels are studied using the model developed here. In order to verify this model, the model-predicted dP/ dx (applied pressure gradient) ∼ Re (Reynolds number) relationship is compared with the experimentally determined dP/ dx∼ Re relationship. Strong agreement between the model predictions and the experimental results supports this model.

Chaotic Mixer for Microchannels

It is difficult to mix solutions in microchannels. Under typical operating conditions, flows in these channels are laminar-the spontaneous fluctuations of velocity that tend to homogenize fluids in turbulent flows are absent, and molecular diffusion across the channels is slow. We present a passive method for mixing streams of steady pressure-driven flows in microchannels at low Reynolds number. Using this method, the length of the channel required for mixing grows only logarithmically with the Péclet number, and hydrodynamic dispersion along the channel is reduced relative to that in a simple, smooth channel. This method uses bas-relief structures on the floor of the channel that are easily fabricated with commonly used methods of planar lithography.