Industrial applications, conductance sensor

Membranes applications in sensors and microelectromechanical systems (MEMS) are increasing in importance in our society. The development of new device able to give rapid detection of chemical and biological species is central to many areas of life science and industrial production. In particular, conducting polymeric materials show major potentiality in this field, and are replacing classical inorganic semiconductor materials because of their better selectivity and rapid measurements, low cost, and easy manufacture for their preparation as films [39]. Moreover, appropriate molecular design of polymer properties can increase the efficiency of the system. 

The classic sensor consists of a housing, connector, NTC, heat-conducting material, and gasket. So far there is no standard in the automotive industry for temperature sensors. In the market we find an endless variety of threads, NTC curves, connectors or cable exit with connector, gasket materials, and housing materials. There are certain trends though (Tab. 7.5.2). In a market survey 35 temperature sensors used by European manufacturers for underhood applications... 

Numerous applications of electrodeless conductivity sensors have been published for the chemical, pulp and paper, aluminum, mining, and food industries. Similar instrumentation has been used for in situ measurements of the salinity of seawater. An instrument for continuous analysis of oleum in the range of 100-102% equivalent sulfuric acid, with an accuracy of 0.01%, is illustrated in Figure 11. A historical review has been published by Light (see Further Reading). 

Conductivity sensors A very significant parameter that gives a measure of the concentration of ions in industrial process streams is conductivity. The continuous measurement of conductivity in process streams is a common practice in the monitoring of boiler feed water, brackish water, demineralization, industrial process media, municipal and industrial wastewater, surface waters, and water treatment. Specific areas of application for conductivity sensors include control of drinking water and ultrapure water quality, determination of nonspecific contaminants, monitoring of salt load in wastewater... 

There are a few examples of CMPs that possess inherent conducting properties. Semi-conductivity can also be introduced in the CMP through doping. Such materials can be very useful in battery applications, the capacitor industries and as sensors such as PAE-derived CMPs (Figure 10.9). The conjugation in these CMP networks makes them suitable for semi-conduction purposes. 

Industrial Applications Color filters black matrix liquid crystal displays photoresist conducting polymer films optical fiber pH sensor printed circuit boards inks textiles ... 

The development of highly selective chemical sensors for complex matrixes of medical, environmental, and industrial interest has been the object of greate research efforts in the last years. Recently, the use of artificial materials - molecularly imprinted polymers (MIPs) - with high recognition properties has been proposed for designing biomimetic sensors, but only a few sensor applications of MIPs based on electrosynythesized conductive polymers (MIEPs) have been reported [1-3]. 

The prospective applications ofmolecular assemblies seem so wide that their limits are difficult to set. The sizes of electronic devices in the computer industry are close to their lower limits. One simply cannot fit many more electronic elements into a cell since the walls between the elements in the cell would become too thin to insulate them effectively. Thus further miniaturization of today s devices will soon be virtually impossible. Therefore, another approach from bottom up was proposed. It consists in the creation of electronic devices of the size of a single molecule or of a well-defined molecular aggregate. This is an enormous technological task and only the first steps in this direction have been taken. In the future, organic compounds and supramolecular complexes will serve as conductors, as well as semi- and superconductors, since they can be easily obtained with sufficient, controllable purity and their properties can be fine tuned by minor adjustments of their structures. For instance, the charge-transfer complex of tetrathiafulvalene 21 with tetramethylquinodimethane 22 exhibits room- temperature conductivity [30] close to that of metals. Therefore it could be called an organic metal. Several systems which could serve as molecular devices have been proposed. One example of such a system which can also act as a sensor consists of a basic solution of phenolophthalein dye 10b with P-cyciodextrin 11. The purple solution of the dye not only loses its colour upon the complexation but the colour comes back when the solution is heated [31]. 

Considering their possible applications in fuel cells, hydrogen sensors, electro-chromic displays, and other industrial devices, there has been an intensive search for proton conducting crystals. In principle, this type of conduction may be achieved in two ways a) by substituting protons for other positively charged mobile structure elements of a particular crystal and b) by growing crystals which contain a sufficient amount of protons as regular structure elements. Diffusional motion (e.g., by a vacancy mechanism) then leads to proton conduction. Both sorts of proton conductors are known [P. Colomban (1992)]. 

Chemical modulation of the surface conductivity is the principle of operation of some of the most commercially successful chemical sensors, the high temperature semiconducting oxide sensors. They are known by their brand name Figaro sensors. They are discussed in detail in Section 8.2.2.1. The reason for their commercial success lies in the fact that their performance and cost match exactly the specific practical needs of many applications, particularly those of the automotive industry. They have been described in great detail, from the point of view of both the underlying physics and chemistry (Morrison, 1994 Logothetis, 1987). 

The four most commonly used LC detectors are the UV detector, the fluorescence detector, the electrical conductivity detector and the refractive index detector. Despite there being a wide range of other detectors to choose from, these detectors appear to cover the needs of 95% of all LC applications. This is because the major use of LC as an analytical technique occurs in research service laboratories and industrial control laboratories where analytical methods have been deliberately developed to utilize the more straight forward and well established detectors that are easy and economic to operate. LC detectors are more compact than their GC counterparts and need much less ancillary support. Most operate solely on the mobile phase and need no other fluid supplies for their effective use. All LC detectors are 3-5 orders of magnitude less sensitive than their GC counterparts and thus sensor contamination is not so severe, and generally less maintenance is required. 

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