Humidity-sensing polymer

Huang J, Viiji S, WeiUer BH, Kaner RB (2004) Nanostructured polyaniline sensors. Chem Eur J 10 1315-1319 Imisides MD, John R, Wallace GG (1996) Microsensors based on conducting polymers. Chemtech 26 19-25 Jain S, Chakane S, Samui AB, Krishnamurthy VN, Bhoraskar SV (2003) Humidity sensing with weak acid-doped polyaniline and its composites. Sens Actuators B 96 124-129 James D, Scott SM, Ali Z, O Hare WT (2005) Chemical sensors for electronic nose systems. Microchim Acta 149 1-17... 

Regarding response and recovery times of polymer-based humidity sensors, one can say that the porosity of the humidity-sensitive polymer is important to obtain quick responses, because the response and recovery times are determined by the time it takes for water vapor to diffuse into or out from a polymer film to reach an equilibrium (Yamazoe and Shimizu 1986). The polymer film should therefore be as thin as possible for quick response. Tsuchitani et al. (1985) believe that, besides the film thickness, an increase in hydrophobicity of the constituent ionic monomer appears to shorten the response time, while the mole fraction of the constituent ionic monomer to non-ionic monomer strongly affects the sensing characteristics. 

O HaUoran GM, van der Vlist W, Sarro PM, French PJ (1999) Influence of the formation parameters on the humidity sensing characteristics of a capadtive humidity sensor based on porous silicon. In CD proceedings of the 13th European conference on solid-state transducers, EUROSENSORS XIII, The Hague, September 12-15, pp 117-120 Otsuki S, Adachi K (1993) Effect of humidity on the fluorescence properties of a medium-sensitive fluorophore in a hydrophilic polymer film. J Photochem Photobiol A Chem 71 169-173... 

On the other hand, most sensing polymers are either hydrophilic or hydrophobic. In the case of humidity sensors, the absorption of water will result in the modification of conductive or dielectric properties with humidity. 

Philipp, L., Mario, W., Sascha, L. Katerina, K. [2010]. Distributed humidity sensing based on rayleigh scattering in polymer optical fibers. Proceedings of SPIE in Fourth European Workshop on Optical Fibre Sensors, Vol. 7653, SPIE, Porto, Portugal, p>p. 1—4. 

Tao, L., Xinyong, D., Chun-Liu, Z. Yang, L. [2010]. Polymer-coated hybrid fiber grating for relative humidity sensing. Proceedings of SPIE in Advanced Sensor Systems and Applications IV, Vol. 7853, SPIE, Beijing, China, pp. 1-6. 

Yeo, T, Sun, T, Grattan, K., Parry, D., Lade, R. Powell, B. [2005a]. Characterisation of a polymer-coated fibre bragg grating sensor for relative humidity sensing. Sensors and Actuators B Chemical Vol. 110(No. 1) 148-156. 

Myounggu P, Flyonny K, Jeffrey PY (2008) Strain-dependent electrical resistance of multi-walled carbon nanotube/polymer composite films. Nanotechnology 19(5) 1-10 Myung JL, Cheol-Jin L, Singh VR, Kum-Pyo Y, Nam-Ki M (2010) Humidity sensing characteristics of plasma functionalized multiwall carbon nanombe-polyimide composite films. Proc IEEE Sens 430-433, art no 4716470... 

OECTs for humidity sensing based on the conducting polymer PEDOTPSS and the proton-conducting film (Nation) were presented by Nilsson et alr The entire sensor was fabricated with solution-processable organic materials and was, therefore, compatible with printing technology (see also Chapter 8.07). 

Interfacial properties cannot be described without identifying the contacting medium. Interfacial properties of a polymer solid are dependent on the conditions under which the surface is equilibrated. The surface configuration of a polymer is a function of the contacting phase of polymer/contacting phase interface. In this context, the conventional sense of surface property (interface with air) is dependent on the history of the surface and the humidity of air. The surface dynamic change occurs when the interfacial equilibrium is broken and is driven by the interfacial tension in the new environment. 

A new Pt(II) polyyne polymer, P15, prepared from the reaction of cfs-[Pt(PPh3)2Cl2] with l,4-diethynyl-2,5-dihexadecyloxybenzene using the extended one pot polymerization route, was tested for its sensing properties and showed fast and reproducible response to relative humidity variations and methanol vapor in surface acoustic-wave (SAW) sensors.46 A SAW sensor was fabricated from polymer P15 as a sensitive membrane, and the polymer was deposited as thin film on the surface of SAW delay lines implemented on three different piezoelectric substrates. High sensitivity and reproducibility were recorded for such devices. The acoustic characterization of the polymer film was also studied with the aid of theoretical results obtained by the perturbation theory. 

The dielectric constants of polar polymers are also extremely sensitive to moisture. Most polar polymers, and especially polymers containing hydrogen-bonding moieties, are susceptible to moisture. Water molecules can become incorporated into them upon exposure to humidity. Water has =80.4 at room temperature. The incorporation of even a small amount of moisture can therefore drastically increase . In addition, is often sensitive to the presence of even small quantities of many common plasticizers, stabilizers and other additives. Very different values are therefore often quoted for the of the same polar polymer. These values may all be "correct", in the sense that, even though they may not describe the "intrinsic properties" of the polymer, they describe the properties of the specimen being tested. 

Almost every sohd state gas sensor exhibits a sensing effect for humidity. Figure 14.21 shows the humidity dependence of a frequency shift of a polymer-type SAW sensor for different sensing fihns. As shown in this hg-ure, the SAW sensor shows comparatively high sensitivity to humidity. Thus, there needs to be an improvement in this regard in order to ameliorate this drawback before SAW sensors can be used in practical applications. - ... 

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