Modelling of Fickian diffusion to enhance polymer-modified sensor performance

McLoughlin, Peter; Flavin, Kevin; Kirwan, Pádraig; Murphy, Brian M.; Murphy, Kieran

doi:10.1016/j.snb.2004.11.099

Cited by 14 publications

(8 citation statements)

References 18 publications

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“…Some reports suggest that the hydrocarbon diffusion coefficient in a polymer is concentration independent, 30 while others have determined the diffusion coefficient to be larger at higher hydrocarbon concentrations. 31 The longer response time observed at high concentrations is probably related to both a swelling and plasticization/polymer chain packing process which is responsible for increasing the film thickness and the analyte path length through the polymer network. 27,29 Consistent with diffusion being slower for larger molecules, the response times were generally higher for naphthalene, pxylene, and ethylbenzene compared to toluene and benzene.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Using Plasticizers to Control the Hydrocarbon Selectivity of a Poly(Methyl Methacrylate)-Coated Quartz Crystal Microbalance Sensor

et al. 2012

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Chemical sensors based on a polymer coated quartz crystal microbalance (QCM) generally present poor molecular selectivity for compounds that contain similar functional groups and possess the same chemical properties. This paper shows for the first time that the selectivity and sensitivity of a poly(methyl methacrylate) (PMMA) based QCM sensor can be significantly enhanced for aromatic hydrocarbons by incorporating a plasticizer into the polymer film. The sensor was fabricated by spin coating PMMA onto a quartz crystal, and the influence of plasticizer type and amount on the response was evaluated. It was shown that the hydrocarbon sensitivity of plasticizer-free PMMA is negligible, while the sensitivity of plasticized PMMA was similar to or in some cases greater relative to highly responsive rubbery polymers such as polyisobutylene (PIB). Detection limits of 4.0, 1.5, 0.4, 0.6, and 0.1 ppm were obtained on a PMMA film containing 25% w/w di(2-ethylhexyl) phthalate for benzene, toluene, ethylbenzene, p-xylene, and naphthalene, respectively. We found that at low plasticizer levels (∼10% w/w) the PMMA film was more sensitive toward ethylbenzene and p-xylene over naphthalene when compared to a PIB film under similar measurement conditions. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) measurements were performed to understand the sensing mechanism, and these studies confirmed a higher hydrocarbon uptake by PMMA in the presence of plasticizer. Positron annihilation lifetime spectroscopy (PALS) studies detected variations in the free volume properties of the polymer films as a function of plasticizer content. The accessible free volume as measured by PALS was significantly less in the PMMA films compared to the PIB, and this result correlates favorably with differences in the QCM response pattern. The QCM results have been rationalized in terms of free volume theory which is responsible for the higher hydrocarbon diffusion/sorption with increased plasticizer content.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Using Plasticizers to Control the Hydrocarbon Selectivity of a Poly(Methyl Methacrylate)-Coated Quartz Crystal Microbalance Sensor

et al. 2012

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“…A number of studies determined the diffusion coefficients of several hydrocarbons in various polymers and showed that this is another important parameter to consider when selecting a particular membrane [ 29 , 35 – 38 ]. McLoughlin and coworkers described the diffusion profile of various chlorinated and aromatic hydrocarbons through a Teflon film, and showed that they obey Fick’s second law of diffusion [ 39 ]. The rate of diffusion of a hydrocarbon molecule through a polymer membrane will depend on its size and structure along with the physicochemical properties of the polymer (i.e., pore size, etc).…”

Section: Principles Of Attenuated Total Reflectance (Atr)mentioning

confidence: 99%

Mid-Infrared Sensing of Organic Pollutants in Aqueous Environments

Pejcic

Myers

Ross

2009

Sensors

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The development of chemical sensors for monitoring the levels of organic pollutants in the aquatic environment has received a great deal of attention in recent decades. In particular, the mid-infrared (MIR) sensor based on attenuated total reflectance (ATR) is a promising analytical tool that has been used to detect a variety of hydrocarbon compounds (i.e., aromatics, alkyl halides, phenols, etc.) dissolved in water. It has been shown that under certain conditions the MIR-ATR sensor is capable of achieving detection limits in the 10–100 ppb concentration range. Since the infrared spectral features of every single organic molecule are unique, the sensor is highly selective, making it possible to distinguish between many different analytes simultaneously. This review paper discusses some of the parameters (i.e., membrane type, film thickness, conditioning) that dictate MIR-ATR sensor response. The performance of various chemoselective membranes which are used in the fabrication of the sensor will be evaluated. Some of the challenges associated with long-term environmental monitoring are also discussed.

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“…Sensor response times may thus be significantly reduced through small increases in temperature. Response times for slowly diffusing analytes may be further reduced, without loss of sensitivity, through the implementation of a predictive Fickian model described by McLoughlin et al 26 Fig. 6b demonstrates how A ' , which is reached after approximately 2 hours, may be predicted using a reduced data set, without loss of measurement accuracy or sensitivity.…”

Section: Determination Of P-nitrochlorobenzenementioning

confidence: 99%

The development of novel organically modified sol-gel media for use with ATR/FTIR sensing

Flavin

Mullowney

Murphy

et al. 2007

Analyst

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The ability to prepare and develop novel pre-concentration media by the sol-gel process, and their integration with mid-infrared transparent waveguides has been demonstrated. This research approach resulted in a mid-infrared sensing methodology in which the properties (porosity, functionality, polarity, etc.) of the recognition layer could be tailored by variation of the sol-gel precursors and processing conditions. Cross-linker type and concentration notably influenced p-xylene absorption and diffusion rate. Unreacted silanol groups appeared to be the dominant factor in the hydrophobicity of sol-gel layers. Variation of sol-gel precursors and thermal treatment altered both film cross-link density and polarity, as demonstrated by variation in the rate of analyte diffusion and equilibrium analyte concentration. The use of a novel 1 : 1 PTMOS : DPDMS material as pre-concentration medium in this analytical sensing approach was validated through the determination of p-nitrochlorobenzene in an aqueous environment. The response demonstrated linearity between 0-30 mg L(-1) with a correlation coefficient of 0.989 and a limit of detection of 0.7 mg L(-1). Sensing times for p-nitrochlorobenzene were also reduced from several hours to 24 minutes, without loss of measurement accuracy or sensitivity, by a 10 degrees C increase in the sensing temperature and the use of a predictive Fickian model previously developed by this research group.

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Modelling of Fickian diffusion to enhance polymer-modified sensor performance

Cited by 14 publications

References 18 publications

Using Plasticizers to Control the Hydrocarbon Selectivity of a Poly(Methyl Methacrylate)-Coated Quartz Crystal Microbalance Sensor

Using Plasticizers to Control the Hydrocarbon Selectivity of a Poly(Methyl Methacrylate)-Coated Quartz Crystal Microbalance Sensor

Mid-Infrared Sensing of Organic Pollutants in Aqueous Environments

The development of novel organically modified sol-gel media for use with ATR/FTIR sensing

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