共查询到20条相似文献,搜索用时 31 毫秒
1.
Isao Kobayashi Yoichi Murayama Takashi Kuroiwa Kunihiko Uemura Mitsutoshi Nakajima 《Microfluidics and nanofluidics》2009,7(1):107-119
This paper reports the production of monodisperse water-in-oil (W/O) emulsions using new microchannel emulsification (MCE)
devices, asymmetric straight-through MC arrays that were hydrophobically modified. The silicon asymmetric straight-through
MC arrays consisted of numerous pairs of microslots and circular microholes whose cross-sectional sizes were 10 μm. This paper
primarily focused on investigating the effect of the osmotic pressure of a dispersed phase (Πd) on MCE. This paper also investigated the effects of the type of continuous-phase oils and the dispersed-phase flux (J
d) on MCE. The dispersed phases were Milli-Q water and Milli-Q water solutions containing sodium chloride. The continuous phases
were decane (as control), hexane, medium chain triacylglyceride (MCT), and refined soybean oil (RSO) solutions containing
tetraglycerin monolaurate condensed ricinoleic acid ester (TGCR) as a surfactant. At Πd of exceeding threshold, highly uniform aqueous droplets with coefficients of variation of less than 3% were stably generated
via hydrophobic asymmetric straight-through MCs. Monodisperse W/O emulsions with average droplet diameters between 32 and
45 μm were produced using the alkane–oil and triglyceride–oil solutions as the continuous phase. This work also demonstrated
that the hydrophobic asymmetric straight-through MC array had remarkable ability to produce highly uniform aqueous droplets
at very high J
d of up to 1,200 L m−2 h−1. 相似文献
2.
Goran T. Vladisavljevi? Isao Kobayashi Mitsutoshi Nakajima 《Microfluidics and nanofluidics》2011,10(6):1199-1209
Uniformly sized droplets of soybean oil, MCT (medium-chain fatty acid triglyceride) oil and n-tetradecane with a Sauter mean diameter of d
3,2 = 26–35 μm and a distribution span of 0.21–0.25 have been produced at high throughputs using a 24 × 24 mm silicon microchannel
plate consisting of 23,348 asymmetric channels fabricated by photolithography and deep reactive ion etching. Each channel
consisted of a 10-μm diameter straight-through micro-hole with a length of 70 μm and a 50 × 10 μm micro-slot with a depth
of 30 μm at the outlet of each channel. The maximum dispersed phase flux for monodisperse emulsion generation increased with
decreasing dispersed phase viscosity and ranged from over 120 L m−2 h−1 for soybean oil to 2,700 L m−2 h−1 for n-tetradecane. The droplet generation frequency showed significant channel to channel variations and increased with decreasing
viscosity of the dispersed phase. For n-tetradecane, the maximum mean droplet generation frequency was 250 Hz per single active channel, corresponding to the overall
throughput in the device of 3.2 million droplets per second. The proportion of active channels at high throughputs approached
100% for soybean oil and MCT oil, and 50% for n-tetradecane. The agreement between the experimental and CFD (Computational Fluid Dynamics) results was excellent for soybean
oil and the poorest for n-tetradecane. 相似文献
3.
Straight-through microchannel devices for generating monodisperse emulsion droplets several microns in size 总被引:1,自引:1,他引:0
Isao Kobayashi Takayuki Takano Ryutaro Maeda Yoshihiro Wada Kunihiko Uemura Mitsutoshi Nakajima 《Microfluidics and nanofluidics》2008,4(3):167-177
The authors recently proposed a promising technique for producing monodisperse emulsions using a straight-through microchannel
(MC) device composed of an array of microfabricated oblong holes. This research developed new straight-through MC devices
with tens of thousands of oblong channels of several microns in size on a silicon-on-insulator plate, and investigated the
emulsification characteristics using the microfabricated straight-through MC devices. Monodisperse oil-in-water (O/W) and
W/O emulsions with average droplet diameters of 4.4–9.8 μm and coefficients of variation of less than 6% were stably produced
using surface-treated straight-through MC devices that included uniformly sized oblong channels with equivalent diameters
of 1.7–5.4 μm. The droplet size of the resultant emulsions depended greatly on the size of the preceding oblong channels.
The emulsification process using the straight-through MC devices developed in this research had very high apparent energy
efficiencies of 47–60%, defined as (actual energy input applied to droplet generation/theoretical minimum energy input necessary
for making droplets) × 100. Straight-through MC devices with numerous oblong microfluidic channels also have great potential
for increasing the productivity of monodisperse fine emulsions. 相似文献
4.
Isao Kobayashi Sayumi Hirose Takanori Katoh Yanping Zhang Kunihiko Uemura Mitsutoshi Nakajima 《Microsystem Technologies》2008,14(9-11):1349-1357
Microchannel (MC) emulsification is a promising technique for producing monodisperse emulsions consisting of highly uniform droplets. The authors developed a high-aspect-ratio microstructure (HARMST) made of poly(methyl methacrylate) (PMMA) as a new MC emulsification device. A PMMA straight-through MC array plate consisting of 31,250 through-holes with a 7.3 × 22.9-μm oblong section and a 200-μm depth was fabricated by a process of synchrotron radiation (SR) lithography and etching. Oblong MCs fabricated in a PMMA straight-through MC array were highly uniform with a coefficient of variation of less than 2%. The fabricated PMMA straight-through MC array plate was used to produce water-in-oil (W/O) emulsions. Monodisperse W/O emulsions with average droplet diameters of approximately 25 μm and a minimum coefficient of variation of 3.2% were produced via a hydrophobic PMMA straight-through MC array. The PMMA straight-through MC array plate also produced monodisperse W/O emulsions at droplet production rates of up to 1.7 × 104/s. The PMMA straight-through MC array plates developed in this work are expected to expand the application field of emulsification using straight-through MC array plates, which have previously been made of single-crystal silicon. 相似文献
5.
Takashi Kuroiwa Hisato Kiuchi Kazuki Noda Isao Kobayashi Mitsutoshi Nakajima Kunihiko Uemura Seigo Sato Sukekuni Mukataka Sosaku Ichikawa 《Microfluidics and nanofluidics》2009,6(6):811-821
We investigated a preparation method of giant vesicles using monodisperse water-in-oil (W/O) emulsions stabilized by bilayer-forming
emulsifiers. A mixture of phosphatidylcholine, cholesterol and stearylamine was used both to stabilize the water droplets
formed in the emulsion and to form the vesicles. Using this lipid mixture, we obtained monodisperse W/O emulsions with mean
droplet diameters of 10–40 μm and coefficients of variation as small as ca 5% by means of the microchannel (MC) emulsification
technique. Utilization of an asymmetric straight-through MC array device enabled a monodisperse droplet productivity of up
to 80 ml/h. The obtained water droplets were converted to giant vesicles via evaporative removal of the continuous-phase solvent
followed by addition of an aqueous buffer solution. The resulting vesicles were similar in size to their starting water droplets,
and a hydrophilic fluorescent marker was entrapped inside the vesicles. 相似文献
6.
Dongming Qiu Laura Silva Anna Lee Tonkovich Ravi Arora 《Microfluidics and nanofluidics》2010,8(4):531-548
Micro-droplet formation from an aperture with a diameter of micrometers is numerically investigated under the cross-flow conditions
of an experimental microchannel emulsification process. The process involves dispersing an oil phase into continuous phase
fluid through a microchannel wall made of apertured substrate. Cross-flow in the microchannel is of non-Newtonian nature,
which is included in the simulations. Micro-droplets of diameter 0.76–30 μm are obtained from the simulations for the apertures
of diameter 0.1–10.0 μm. The simulation results show that rheology of the bulk liquid flow greatly affects the formation and
size of droplets and that dispersed micro-droplets are formed by two different breakup mechanisms: in dripping regime and
in jetting regime characterized by capillary number Ca. Relations between droplet size, aperture opening size, interfacial
tension, bulk flow rheology, and disperse phase flow rate are discussed based on the simulation and the experimental results.
Data and models from literature on membrane emulsification and T-junction droplet formation processes are discussed and compared
with the present results. Detailed force balance models are discussed. Scaling factor for predicting droplet size is suggested. 相似文献
7.
Katerina Butron Fujiu Isao Kobayashi Kunihiko Uemura Mitsutoshi Nakajima 《Microfluidics and nanofluidics》2011,10(4):773-783
Microchannel (MC) emulsification is a promising technique to produce monodisperse emulsions by spontaneous interfacial-tension-driven
droplet generation. The purpose of this study was to systematically characterize the effect of temperature on droplet generation
by MC emulsification, which is a major uncharted area. The temperature of an MC emulsification module was controlled between
10 and 70°C. Refined soybean oil was used as the dispersed phase and a Milli-Q water solution containing sodium dodecyl sulfate
(1 wt%) as the continuous phase. Monodisperse oil-in-water (O/W) emulsions with a coefficient of variation below 4% were produced,
and at all the operating temperatures, their average droplet diameter ranged from 32 to 38 μm. We also investigated the effect
of flow velocity of the dispersed phase on droplet generation characteristics. The maximum droplet generation rate (frequency)
from a channel at 70°C exceeded that at 10°C by 8.1 times, due to the remarkable decrease in viscosity of the two phases.
Analysis using dimensionless numbers indicated that the flow of the dispersed phase during droplet generation could be explained
using an adapted capillary number that includes the effect of the contact angle of the dispersed phase to the chip surface. 相似文献
8.
Production of uniform droplets using membrane, microchannel and microfluidic emulsification devices 总被引:1,自引:1,他引:0
G. T. Vladisavljevi? Isao Kobayashi Mitsutoshi Nakajima 《Microfluidics and nanofluidics》2012,13(1):151-178
This review provides an overview of major microengineering emulsification techniques for production of monodispersed droplets. The main emphasis has been put on membrane emulsification using Shirasu Porous Glass and microsieve membrane, microchannel emulsification using grooved-type and straight-through microchannel plates, microfluidic junctions and flow focusing microfluidic devices. Microfabrication methods for production of planar and 3D poly(dimethylsiloxane) devices, glass capillary microfluidic devices and single-crystal silicon microchannel array devices have been described including soft lithography, glass capillary pulling and microforging, hot embossing, anisotropic wet etching and deep reactive ion etching. In addition, fabrication methods for SPG and microseive membranes have been outlined, such as spinodal decomposition, reactive ion etching and ultraviolet LIGA (Lithography, Electroplating, and Moulding) process. The most widespread application of micromachined emulsification devices is in the synthesis of monodispersed particles and vesicles, such as polymeric particles, microgels, solid lipid particles, Janus particles, and functional vesicles (liposomes, polymersomes and colloidosomes). Glass capillary microfluidic devices are very suitable for production of core/shell drops of controllable shell thickness and multiple emulsions containing a controlled number of inner droplets and/or inner droplets of two or more distinct phases. Microchannel emulsification is a very promising technique for production of monodispersed droplets with droplet throughputs of up to 100?l?h?1. 相似文献
9.
Bin Xiao Tao Dong Einar Halvorsen Zhaochu Yang Yulong Zhang Nils Hoivik Dandan Gu Nhut Minh Tran Henrik Jakobsen 《Microsystem Technologies》2011,17(1):115-125
This paper presents the design and fabrication of a micro Pirani gauge using VO
x
as the sensitive material for monitoring the pressure inside a hermetical package for micro bolometer focal plane arrays
(FPAs). The designed Pirani gauge working in heat dissipating mode was intentionally fabricated using standard MEMS processing
which is highly compatible with the FPAs fabrication. The functional layer of the micro Pirani gauge is a VO
x
thin film designed as a 100 × 200 μm pixel, suspended 2 μm above the substrate. By modeling of rarefied gas heat conduction
using the Extended Fourier’s law, finite element analysis is used to investigate the sensitivity of the pressure gauge. Also
the thermal interactions between the micro Pirani gauge and bolometer FPAs are verified. From the fabricated prototype, the
measured device TCR is about −0.8% K−1 and the sensitivity about 1.84 × 10−3 W K−1 mbar−1. 相似文献
10.
E. Leclerc H. Kinoshita T. Fujii D. Barthès-Biesel 《Microfluidics and nanofluidics》2012,12(5):761-770
The study deals with a microfluidic method to investigate the transient behavior of microcapsules in flow. The technique consists
of investigating ovalbumin microcapsules passing through a convergent–divergent microchannel made of PolyDiMethylSiloxane.
We work with three types of square microchannel with, respectively, cross section values of h × h = 30 × 30, 50 × 50 and 70 × 70 μm. The microchannels length is L = 3h. We analyze the kinetics of deformation of the microcapsules in the microchannels for velocity ranging from 2 to 5 cm/s and
for microcapsule size ratio d/h ranging from 0.9 to 2.5. The relaxation process at the pore outlet is modeled using an exponential relaxation law. We show
that that the relaxation time at the divergent outlet depends on the microcapsule size ratio d/h. Thanks to the analytical expression of the relaxation, we extract a shear modulus of the membrane equal to 0.04 N/m. This
value is consistent with the value of 0.07 N/m that we found using the steady state analysis performed in cylindrical glass
capillaries. Thus, it is interesting to notice that the microcapsule behavior based on a simple analytical model can be successfully
described despite the complex flow situation consisting of deformable microcapsule in confined square microchannels. 相似文献
11.
Cheng-Che Chung I-Fang Cheng Chi-Chang Lin Hsien-Chang Chang 《Microfluidics and nanofluidics》2011,10(2):311-319
We studied an imaging-based technique for the rapid quantification of bio-particles in a dielectrophoretic (DEP) microfluidic
chip. Label-free particles could be successively sorted and trapped in a continuous flow manner under the applied alternating
current (AC) conditions. Both 2 and 3 μm polystyrene beads at a concentration of 1.0 × 107 particles ml−1 could be rapidly quantified within 5 min in our DEP system. Capturing efficiencies higher than 95% could be 2 μm polystyrene
beads with a linear flow speed, applied voltage and frequency of 0.89 mm s−1, 20 Vp-p and 5 MHz. Yeast cells (Candida glabrata and Candida albicans) could also be captured even at a lower concentration of 2.5 × 105 cells ml−1. Images of aggregative particles taken from the designed trapping area were further processed based on the intensity of relative
greyscale followed by correction of the particle numbers. The imaging-based quantification method showed higher agreement
than that of the conventional counting chamber method and proved the stability and feasibility of our AC DEP system. 相似文献
12.
Customized trapping of magnetic particles 总被引:1,自引:1,他引:0
This paper presents an efficient technique for trapping of magnetic particles in confined spatial locations using customized
designs of micro-coils (MCs). Large magnetic field gradients of up to 20 T/mm and large magnetic forces in the range of 10−8 Newton on magnetic particles with diameter of 1 μm have been achieved using MCs with several planar geometrical configurations.
A large magnetic field gradient is generated and enhanced by two structural parameters: the small width and high aspect ratio
of each single conductor and the ferromagnetic pillars positioned at high-flux density locations. This arrangement creates
very steep magnetic potential wells, in particular at the vicinity of the pillars. The system allowed capturing of suspended
magnetic particles as far as 1,000 μm from the center of the device. Magnetic particles/cells have been trapped and confined
in single and in arrays of deep magnetic potential wells corresponding to the MCs configuration. 相似文献
13.
This work presents a polydimethylsiloxane (PDMS) microfluidic device for packaging CMOS MEMS impedance sensors. The wrinkle
electrodes are fabricated on PDMS substrates to ensure a connection between the pads of the sensor and the impedance instrument.
The PDMS device can tolerate an injection speed of 27.12 ml/h supplied by a pump. The corresponding pressure is 643.35 Pa.
The bonding strength of the device is 32.44 g/mm2. In order to demonstrate the feasibility of the device, the short circuit test and impedance measurements for air, de-ionized
water, phosphate buffered saline (PBS) at four concentrations (1, 2 × 10−4, 1 × 10−4, and 6.7 × 10−5 M) were performed. The experimental results show that the developed device integrated with a sensor can differentiate various
samples. 相似文献
14.
Dae Sung Yoon Yoon-Kyoung Cho Kwang W. Oh Sunhee Kim Young Ah Kim Jung Im Han Geunbae Lim 《Microsystem Technologies》2006,12(3):238-246
We have fabricated a microfluidic gel valve device that used reversible sol–gel transition of methyl cellulose (MC). A microheater
and a microtemperature sensor were implemented in each microchannel in the gel valve device. Before evaluating the performance
of the gel valve device, various properties of the MC solution were investigated using viscometer, spectrophotometer, and
NMR. Gelation temperature was increased as the MC concentration was increased. Clear gel, an intermediate state between clear
sol and turbid gel, was found at the temperature range from 30–40°C to 50–60°C. Temperature at each microchannel of the device
was measured and the effect of the temperature difference on the valve operation was elucidated. In order to have normal operation
of the gel valve, it was important to keep the temperature of the heated microchannel around 60°C while keeping the temperature
of the flowing microchannel below 35°C. The temperature difference between two microchannels was about 23 K when fan forced
cooling (FFC) method was used. For normal performance of the gel valve device, a temporary pause of fluid flow for at least
5 s was required to complete the local gelation in the microchannel. Stable gel valve performance was obtained at the flow
rates larger than 5 μl/min. The gel valve device showed no leakage up to 2.07×104 Pa. 相似文献
15.
Jayaprakash Sivasamy Yong Cai Chim Teck-Neng Wong Nam-Trung Nguyen Levent Yobas 《Microfluidics and nanofluidics》2010,8(3):409-416
This article reports a design that reliably adds reagents into droplets by exploiting the physics of fluid flow at a T-junction
in the microchannel. An expanded section right after the T-junction enhances merging of a stream with a droplet, eliminates
the drawbacks such as extra droplet formation and long mixing time. The expanded section reduces the pressure buildup at the
T-junction and minimizes the tendency to form extra droplets; plays the role in creating low Laplace pressure jump across
the interface of the droplet forming from the T-junction which reduces the probability of forming extra droplet in the merging
process; provides space for droplet coalescence if there is an extra droplet due to droplet break-up before merging. In this
design, after merging, the reactants are in axial arrangement inside the droplets which lead to faster mixing. Reliable addition
of reagent to the droplets happens for the combination of flow rates in a broad range from 25 to 250 μl/h, for both DI water
(Q
DI) and fluorescent (Q
fluo) streams. 相似文献
16.
Scalable attoliter monodisperse droplet formation using multiphase nano-microfluidics 总被引:1,自引:1,他引:0
We demonstrate a robust method to produce monodisperse femtoliter to attoliter droplets by using a nano-microfluidic device.
Two immiscible liquids are forced through a nanochannel where a steady nanoscopic liquid filament forms, thinning close to
the nanochannel exit to a microchannel due to the capillary focusing. When the nanoscopic filament enters the microchannel,
monodisperse droplets are formed by capillary instability. In a certain range of physical parameters and geometrical configurations,
the droplet size is only determined by the nanochannel height and independent of liquid flow rates and ratios, surfactants,
and continuous phase viscosity. By using nanochannels with a height of 100–900 nm, 0.4–3.5 μm diameter droplets (volume down
to 30 aL) have been produced. The generated droplets are stable for at least weeks. 相似文献
17.
Vibration feedback is one of the most popular ways to communicate between human and haptic interfaces nowadays. In order to
deliver a wider variety of information accurately and efficiently, significant design factors of the vibration need to be
investigated and applied to haptic devices. In this study, the excitatory direction was examined as a design factor of the
vibration in terms of sensitivity and emotion. We conducted two experiments. In the first experiment, the sensitivities of
three excitatory directions—X (lateral), Y (fore-and-aft) and Z (vertical) axes were estimated by the absolute thresholds of the vibration perception with two frequency levels (150 and
280 Hz). Based on ten participants’ estimated absolute thresholds, we conclude that the vibration with X axis is less sensitive than Z axis at the frequency of 150 Hz, while the vibration with Y axis is less sensitive than Z axis at the frequency of 280 Hz. In the second experiment, the agreeability of 29 emotional expressions to the vibrations
was measured by a 7-point scale with a total of 12 conditions (2 frequencies × 2 amplitudes (i.e., 50 × 10−3 and 500 × 10−3 g) × 3 excitatory directions). Based on 20 participants’ responses, it is concluded that at the frequency of 150 Hz and the
amplitude of 50 × 10−3 g, the vibration is perceived as ‘light’, and as even ‘lighter’ if the vibration is with Y axis rather than with Z axis. Likewise, at the frequency of 150 Hz and the amplitude of 500 × 10−3 g, the vibration is perceived as ‘repulsive’, and as even ‘more repulsive’ if the vibration is with Y or Z axis rather than with X axis. Therefore, three excitatory directions can be selectively utilized to design the distinguishable vibration by its sensitivity
and emotion. 相似文献
18.
A fully resolved numerical simulation of a turbulent microchannel flow, with uniformly spaced two-dimensional obstruction
elements mounted at the wall and normal to the flow direction, was carried out at a very low Reynolds number of Re ≃ 970 based on the centerline velocity and the microchannel height. Employing the lattice Boltzmann numerical technique,
all energetic scales of turbulence were resolved with about 19 × 106 grid points (1261 × 129 × 128 in the x
1, x
2, and x
3 directions). The simulated results confirm the self-maintenance of turbulence at such a low Reynolds number. Turbulence persisted
over more than 1,000 turnover times, which was sufficiently long to prove its self-maintenance. These findings support the
conjecture that turbulence developing in microchannels having rough walls can not only be initiated but also maintained at
very low Reynolds numbers. 相似文献
19.
Microfluidic devices with micro-sieve plate as the dispersion medium have been widely used for the mass production of emulsions.
While unfortunately, few studies have so far been made for the droplet generation rules in those devices. In this work, the
droplet generation processes in micro-sieve dispersion devices are investigated with specially designed micro-sieve pore arrays.
The effects of channel structure, pore arrangement, and feeding method of dispersed phase on the average size and distribution
of droplets are studied carefully. It is found the dimensionless average droplet diameters (d
av/d
e) in micro-sieve dispersion devices can be represented by a linear relation with Ca−1/4 of continuous phase, the same as the scaling law in T-junction microchannels. The flow distribution among pores and the steric
hindrance between droplets affect the diameter distribution of generated droplet very much. Monodispersed droplets with polydispersity
index less than 5% can be made at Ca number larger than 0.01 and phase ratio (Q
D/Q
C) less than 1/6 in the present investigation. 相似文献
20.
S. M. Sohel Murshed Say Hwa Tan Nam Trung Nguyen Teck Neng Wong Levent Yobas 《Microfluidics and nanofluidics》2009,6(2):253-259
This paper reports experimental investigations on the droplet formation and size manipulation of deionized water (DIW) and
nanofluids in a microfluidic T-junction at different temperatures. Investigations of the effect of microchannel depths on
the droplet formation process showed that the smaller the depth of the channel the larger the increase of droplet size with
temperature. Sample nanofluids were prepared by dispersing 0.1 volume percentage of titanium dioxide (TiO2) nanoparticles of 15 nm and 10 nm × 40 nm in DIW for their droplet formation experiments. The heater temperature also affects
the droplet formation process. Present results demonstrate that nanofluids exhibit different characteristics in droplet formation
with the temperature. Addition of spherical-shaped TiO2 (15 nm) nanoparticles in DIW results in much smaller droplet size compared to the cylindrical-shaped TiO2 (10 nm × 40 nm) nanoparticles. Besides changing the interfacial properties of based fluid, nanoparticles can influence the
droplet formation of nanofluids by introducing interfacial slip at the interface. Other than nanofluid with cylindrical-shaped
nanoparticles, the droplet size was found to increase with increasing temperature. 相似文献