Vapor sensitive polymer

The contributed chapters are divided into three sections. The first section is dedicated to chemical vapor sensing. In the majority of the photonic vapor sensors described here, a layer of vapor sensitive material (polymer, ceramics, or colloidal... 

Though not strictly functioning as resistors/conductors, carbon nanotubes have just been reported in an extraordinarily vapor-sensitive capacitive device [19]. The electric field lines emanating from the nanotubes are responsible for a localized dielectric response that can be modulated by minute quantities of adsorbate on the nanotube surface. A layer of hydrogen-bonding polymer, or even a mono-layer terminated in mildly acidic groups, increased sensitivity to parts per billion levels. Response strength was correlated with the dipole moment of the analytes. 

The sensitivity of these sensors was defined as a signal change upon exposure to the known concentrations of vapors. Sensitivity of the 2.8-nm CdSe nanocrystals was 0.8 PL counts/Torr of methanol with almost no detectable sensitivity to toluene. The sensitivity of the 5.6-nm CdSe nanocrystals was 2.9 PL counts/Torr of methanol and 8.8PL counts/Torr of toluene. Although this environmental sensitivity was compatible with earlier reported sensors based on polished or etched bulk CdSe semiconductor crystals3940 and polymer-nanocrystals composites,16 the sensor reported here had a more selective response to polar and nonpolar vapors due to the multiwavelength PL from different-size nanocrystals incorporated into the polymer film. The response and recovery kinetics of PL from the 2.8-nm nanocrystals in PMM A upon exposure to methanol were very fast (<0.5 min). However, 5.6-nm nanocrystals in the same sensor film exhibited a much longer response and recovery times upon interactions with methanol, 4 and 20min, respectively. The 5.6-nm nanocrystals had 4-min response and 0.5-min recovery times upon interactions with toluene. 

Experiment has shown that the electronic conduction of the VOC sensing metal nanoparticle films is also dependant on the metal core size itself and how the nanoparticles are linked to other polymer molecules (Leibowitz et al. 1999 Zheng et al. 2000 Han et al. 2001) (see Fig. 4,7). Brust et al. (1994) studied electronic transport properties, chemical composition, and the vapor sensitivity of l,n-alkylenedithiol interlinked gold nanoparticles films as a function of alkylene chain length and... 

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. 

At processing temperatures, most polymers emit fumes and vapors that may be irritating to the respiratory tract. This is also tme for PVC and its additives. Such irritation may extend to the skin and eyes of sensitive people. Processing emissions exposure can also be greatly reduced or eliminated by the use of properly designed and maintained exhaust ventilation. 

Ethyl Vinyl Ether. The addition of ethanol to acetylene gives ethyl vinyl ether [104-92-2] (351—355). The vapor-phase reaction is generally mn at 1.38—2.07 MPa (13.6—20.4 atm) and temperatures of 160—180°C with alkaline catalysts such as potassium hydroxide and potassium ethoxide. High molecular weight polymers of ethyl vinyl ether are used for pressure-sensitive adhesives, viscosity-index improvers, coatings and films lower molecular weight polymers are plasticizers and resin modifiers. 

UV-induced surface grafting of a polymer sheet using vapor phase transfer of sensitizer and monomer from a volatile solution (9). 

In the continuous process the solution of sensitizer and monomer forms a thin surface layer on the polymer in which the photoinitiated reaction takes place without affecting the bulk phase of the polymer. In the vapor phase process, the grafting reaction starts at the... 

Another mechanism for alkanone-sensitized photodehydrochlorination comprises Norrish type I scission of the ketone, followed by ground-state reactions of radicals (19). However, the evidence for such a mechanism is based on experiments that were carried out in the vapor phase (19). Initiation of the photodegradation of PVC by hexachloroacetone has been suggested to involve the abstraction of hydrogen from the polymer by radicals resulting from the photolysis of the ketone s carbon-chlorine bonds (22). 

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