Transient molecular diffusion in microfluidic channels: Modeling and experimental verification of the results

Hollow-Core Photonic Crystal Fibres (HC-PCFs) have emerged as an area of interest for fibre-optic based distributed gas sensing. In order to allow the gas to enter the hollow core of the fibre, various techniques such as lateral drilled side holes have been investigated in the literature. However, it is essential to understand the mechanisms of gas flow in HC-PCFs with drilled side holes in order to determine the optimum design parameters of the sensor such as the size and spacing of drilled side holes. This study aims to analyse the gas flow behaviour and determine the response time of HC-PCFs with drilled side holes by developing and applying a numerical model based on gas diffusion in a microchannel. The model is validated against the results of two different experimental studies. The model is then applied to determine the response time is a function of the length, the number and spacing of side holes and the gas type (methane and acetylene). It is found that an inverse relationship exists between the effects of number and spacing of side holes on the response time and the optical loss, suggesting that an optimum design point exists.

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“…This is because of the higher diffusivity of methane compared to acetylene. This is in agreement with the results of other studies [35,36].…”

Section: Gas Flow In Single Drilled Hc-pcfsupporting

confidence: 94%

Numerical analysis of gas diffusion in drilled Hollow-Core Photonic Crystal fibres

et al. 2018

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“…The response of the gas sensor incorporated in the microcavity located at the channel end ( Fig. 1a ) is continuously recorded from t = -5 s to t = 200 s. The relationship between such temporal response profiles and the diffusion rates through the channel has been the subject of discussion in a number of publications from our laboratory 52 53 54 , but in the present work such responses are utilized only for comparing the permeabilities of the test and control microchannels to the target gas.…”

Section: Resultsmentioning

confidence: 99%

The selective flow of volatile organic compounds in conductive polymer-coated microchannels

Hossein‐Babaei

Zare

2017

Sci Rep

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Many gaseous markers of critical biological, physicochemical, or industrial occurrences are masked by the cross-sensitivity of the sensors to the other active components present at higher concentrations. Here, we report the strongly selective diffusion and drift of contaminant molecules in air-filled conductive polymer-coated microfluidic channels for the first time. Monitoring the passage of different target molecules through microchannels coated with Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) revealed that contaminants such as hexane, benzene, and CO pass through the channel unaffected by the coating while methanol, ethanol, and partly acetone are blocked. The observations are explained with reference to the selective interactions between the conductive polymer surface and target gas molecules amplified by the large wall/volume ratio in microchannels. The accumulated quantitative data point at the hydrogen bonding as the mechanism of wall adsorption; dipole-dipole interactions are relatively insignificant. The presented model facilitates a better understanding of how the conductive polymer-based chemical sensors operate.

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“…Thus, the performance of microfluidic-based devices is dependent on the diffusivity and physical adsorption/desorption of gas molecules from and to the channel walls. The temporal variation of analytes concentration along the channel at isothermal and isobar conditions can be determined by this expression [ 257 , 258 , 259 ]:

where D is the diffusion coefficient of each analyte in the mixture and

is the concentration of gas molecules physiosorbed into the walls of the channel. The previous equation is valid from channel depths or diameters ranging between 1 mm and 1 µm.…”

Section: Microanalytical Tools For Vocs Discriminationmentioning

confidence: 99%

“…Nonetheless, the previous expression is unable to describe the diffusion processes in ultrathin channels ( d < 1 µm), where other physical mechanisms should be taken into account [ 259 ]. According to literature, if a microfluidic channel with circular cross-section is considered, the concentration loss

due to the physisorption effect can be represented by the following expression [ 257 ]:

where

is the number of the surface adsorption sites available per unit volume of the channel,

is the effective channel depth, and

is generally defined as the physisorption constant, which is directly related to the nature of analytes. Combining the physisorption expression to the diffusion equation initially stated, the so-called diffusion-physisorption equation can be formulated, which gives the change in analytes concentration over time and along the microfluidic channel [ 255 , 257 ]:

…”

Section: Microanalytical Tools For Vocs Discriminationmentioning

confidence: 99%

Advancements in Microfabricated Gas Sensors and Microanalytical Tools for the Sensitive and Selective Detection of Odors

Ollé

Farré-Lladós

Casals‐Terré

2020

Sensors

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In recent years, advancements in micromachining techniques and nanomaterials have enabled the fabrication of highly sensitive devices for the detection of odorous species. Recent efforts done in the miniaturization of gas sensors have contributed to obtain increasingly compact and portable devices. Besides, the implementation of new nanomaterials in the active layer of these devices is helping to optimize their performance and increase their sensitivity close to humans’ olfactory system. Nonetheless, a common concern of general-purpose gas sensors is their lack of selectivity towards multiple analytes. In recent years, advancements in microfabrication techniques and microfluidics have contributed to create new microanalytical tools, which represent a very good alternative to conventional analytical devices and sensor-array systems for the selective detection of odors. Hence, this paper presents a general overview of the recent advancements in microfabricated gas sensors and microanalytical devices for the sensitive and selective detection of volatile organic compounds (VOCs). The working principle of these devices, design requirements, implementation techniques, and the key parameters to optimize their performance are evaluated in this paper. The authors of this work intend to show the potential of combining both solutions in the creation of highly compact, low-cost, and easy-to-deploy platforms for odor monitoring.

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Transient molecular diffusion in microfluidic channels: Modeling and experimental verification of the results

Cited by 15 publications

References 36 publications

Numerical analysis of gas diffusion in drilled Hollow-Core Photonic Crystal fibres

Numerical analysis of gas diffusion in drilled Hollow-Core Photonic Crystal fibres

The selective flow of volatile organic compounds in conductive polymer-coated microchannels

Advancements in Microfabricated Gas Sensors and Microanalytical Tools for the Sensitive and Selective Detection of Odors

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