title: Determination of hydrocarbons using sapphire fibers coated with poly(dimethylsiloxane).
abstract: A poly(dimethylsiloxane) (PDMS) coated sapphire fiber has been investigated as a sensor for hydrocarbons (HCs) in the mid-infrared region around 3000 cm(-1). In order to optimize and predict sensor response, the diffusion behavior of the analytes into the PDMS preconcentration medium has been examined. A diffusion model based on Fickian diffusion was used to quantify diffusion. The model incorporated such factors as film thickness, refractive index of the polymer and the fiber core, and principal wavelength at which the analyte absorbs. A range of hydrocarbons, from hexane to pentadecane, was analyzed at 2930 cm(-1) using both fiber-coupled Fourier transform infrared spectroscopy and a modular prototype system. Diffusion coefficients were determined for these compounds and diffusion behavior examined and related to factors such as analyte polarity and molecular size. The diffusion coefficients were found to range from 6.41 x 10(-11) 5 x 10(-12) to 5.25 x 10(-11) +/- 9 x 10(-13) cm2 s(-1) for hexane and pentadecane into a 2.9 microm PDMS film, respectively. The diffusion model was also used to examine the effect of changing system parameters such as film thickness in order to characterize sensor response.
authors.affiliation: Waterjord Institute of Technology, Cork Road, Waterford City, Ireland.
authors.forename: Rhona
authors.initials: R
authors.lastname: Howley
authors.forename: B D
authors.initials: BD
authors.lastname: MacCraith
authors.forename: Kieran
authors.initials: K
authors.lastname: O'Dwyer
authors.forename: Hugh
authors.initials: H
authors.lastname: Masterson
authors.forename: P
authors.initials: P
authors.lastname: Kirwan
authors.forename: Peter
authors.initials: P
authors.lastname: McLoughlin
mesh_terms: D000537:Aluminum Oxide; D020099:Coated Materials, Biocompatible / Q000138:chemical synthesis / Q000737:chemistry*; D003198:Computer Simulation; D004058:Diffusion; D004129:Dimethylpolysiloxanes; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005336:Fiber Optic Technology / Q000295:instrumentation*; D006838:Hydrocarbons / Q000032:analysis* / Q000737:chemistry; D008420:Manufactured Materials; D008956:Models, Chemical; D012828:Silicones; D017550:Spectroscopy, Fourier Transform Infrared / Q000295:instrumentation* / Q000379:methods; D014159:Transducers
chemical_list: D020099:Coated Materials, Biocompatible; D004129:Dimethylpolysiloxanes; D006838:Hydrocarbons; D012828:Silicones; C013830:baysilon; D000537:Aluminum Oxide