بهره برداری از اطلاعات فضایی و زمانی و بهینه سازی هندسی عملکرد سیگنال / نویز با استفاده از آرایه های سیاه و سفید پلیمری ردیاب بخار کامپوزیت کربن

We have investigated various aspects of the geometric and spatiotemporal response properties of an array of sorption-based vapor detectors. The detectors of specific interest are composites of insulating organic polymers filled with electrical conductors, wherein the detector film provides a reversible dc electrical resistance change upon the sorption of an analyte vapor. An analytical expression derived for the signal/noise performance as a function of detector volume implies that there is an optimum detector film volume which will produce the highest signal/noise ratio for a given carbon black-polymer composite when exposed to a fixed volume of sampled analyte. This prediction has been verified experimentally by exploring the response behavior of detectors having a variety of different geometric form factors. We also demonstrate that useful information can be obtained from the spatiotemporal response profile of an analyte moving at a controlled flow velocity across an array of chemically identical, but spatially nonequivalent, detectors. Finally, we demonstrate the use of these design principles, incorporated with an analysis of the changes in detector signals in response to variations in analyte flow rate, to obtain useful information on the composition of analytes and analyte mixtures.

Arrays of vapor detectors that rely on the partially selective interaction of vapors with various polymers have received significant attention in the recent literature. Detector types of interest include carbon black-insulating polymer composites [1], conducting organic polymers [2], [3] and [4], polymer-coated quartz crystal microbalances (QCM) [5], polymer-coated surface acoustic wave (SAW) devices [6] and [7], polymer-coated capacitors [8], and arrays of dye-impregnated polymeric beads or coated optical fibers [9], [10] and [11]. The responses of such sorption-based detectors depend primarily on the partition coefficient of the gaseous analyte into the polymer [12]. Arrays of detectors, in which each element contains a chemically different polymer, have been demonstrated to allow discrimination between various vapors based on the differences in response patterns produced by the detector array [13]. In most studies to date, the detectors in such an array are placed in nominally spatially equivalent positions relative to the analyte flow path [1], [11] and [14]. In such a configuration, any spatiotemporal differences between detectors are minimized, and the array response pattern is determined by the differing physicochemical responses of the various detectors towards the analyte of interest. The variations in analyte sorption amongst various detectors thus determines the resolving power of the detector array and determines the other performance parameters of such systems. In this work, we have deliberately placed detectors in spatially nonequivalent positions relative to the flow path of the sampled analyte. We demonstrate that the spatiotemporal response properties of such an array can be used advantageously to obtain information on the identity of analyte vapors and also to produce information on the composition of analyte mixtures. Additionally, in most studies of detector arrays to date, the form factor of the individual detectors is constrained by factors related to the mode of signal transduction. For example, most film-coated QCM devices must have specified dimensions so that a resonant bulk acoustic wave can be maintained in the quartz crystal transducer element [15] and [16]. Similarly, the geometry of SAW devices is constrained by the need to sustain a Rayleigh wave of the appropriate resonant frequency at the surface of the transducer crystal [15]. Each detector in a QCM or SAW array typically has an identical area and form factor; consequently, the array response is based solely on the different polymer/analyte sorption properties of the differing detector films. Although in principle these types of devices could be constructed with a range of form factors, relatively little attention has been focused on varying the form factors of the detector to optimize the signal/noise ratio (S/N) for a particular analyte. Recent work in our laboratories has focused on the use of chemically sensitive vapor detectors comprised of regions of electrical conductors interspersed amongst regions of insulating organic polymers [1]. The swelling of these films upon sorption of an analyte vapor produces a readily measured, dc electrical resistance change. Spray-coating deposition techniques using masked substrates permits the fabrication of such chemiresistor-type vapor detectors in virtually any geometry where the film can bridge two electrically conducting contact leads [17]. This freedom to explore various form factors allows convenient exploration of the geometrical aspects of sorption-based vapor detector design. We demonstrate herein that different form factors of a given detector film in conjunction with specific types of analyte flow paths can provide very different detection performance for different types of analyte vapors. An analytical expression has been derived to predict the optimum volume of a detector film as a function of the sample volume and the analyte/polymer partition coefficient. Under certain conditions, detectors of very small areas are expected to have the best S/N performance, whereas for other conditions, relatively large detector areas are optimal. These predictions have been verified through measurements of the response properties of conducting polymer composite chemiresistor vapor detectors. We also demonstrate that, based on these principles, the use of an array of detectors that are nominally identical chemically, but which have different form factors relative to the analyte flow path, can provide useful information on the composition and identity of an analyte vapor. Finally, we report S/N data that allow comparisons between the detection limits of several polymer/analyte combinations using two different modes of signal transduction: frequency shifts in SAW devices and dc electrical resistance changes in composites of carbon black and insulating organic polymers.

The dependence of the relative power spectral density on the volume of carbon black-polymer composite vapor detectors was of the form View the MathML source, with n=1 for PEVA-carbon black detectors and n=0.6 for PCL-carbon black detectors in the frequency range of 1–800 Hz. Analytes with moderate polymer/gas partition coefficients produce the same ΔR/Rb response values on detectors of constant film thickness but of different area, so under these conditions the S/N is optimized for detectors of very large area. In contrast, for finite quantities of injected sample, analytes with high polymer/gas partition coefficients produce much larger ΔR/Rb values on detectors of small area that are positioned to best sample the injected analyte flow. For such detector/analyte combinations, detectors of small area will exhibit significantly better vapor detection sensitivity. Manipulation of the geometric form factor of carbon black composite vapor detectors thus provides a facile method for optimizing the S/N performance for a particular detector/analyte combination of interest. An array of nominally identical polymer-carbon black detectors arranged linearly relative to the analyte flow path produces different spatiotemporal response patterns for analytes having different polymer/gas partition coefficients. Analytes with moderate polymer/gas partition coefficients produce the same signals on all detectors over a range of flow rates, whereas before steady state is reached on all of the detectors, analytes with very large polymer/gas partition coefficients produce signals that are highly dependent on the analyte flow rate and the spatial position of the detector in the array. Such a configuration produces useful information on the composition of binary analyte mixtures and adds classification information to an array of compositionally different conducting polymer composite vapor detectors.