Plasma polymerized acetaldehyde thin films for retention of volatile organic compounds

Abstract

Recebido em 10/8/07; aceito em 31/1/08; publicado na web em 20/8/08PLASMA POLYMERIZED ACETALDEHYDE THIN FILMS FOR RETENTION OF VOLATILE ORGANIC COMPOUNDS. The aim of this work is the production and characterization of plasma polymerized acetaldehyde thin films. These films show highly polar species, are hydrophilic, organophilic and easily adsorb organic reactants with CO radicals but only allow permeation of reactants with OH radicals. The good step coverage of films deposited on aluminum trenches is useful for sensor development. Films deposited on hydrophobic substrates may result in a discontinued layer, which allows the use of preconcentration in sample pretreatment. Deposition on microchannels showed the possibility of chromatographic columns and/or retention system production to selectively detect or remove organic compounds from gas flows.

Comparison of adsorbent films obtained by plasma polymerization of oxygenated organic compounds

“…While methyl acetate, ethyl acetate and ethyl ether can adsorb differently reactants of distinct polarity (see Table 4), only acetaldehyde and 2-propanol films act like a selective membrane for polar organic compounds, as previously determined by Nascimento et al [20], Lima et al [19] and Hernandez et al [22]. A semi-quantitative adsorption scale was done using QCM data and is shown in Table 4.…”

“…Quartz crystal measurements (QCM) were carried out [19][20][21][22][23]26] with organic compounds in a large range of polarity in order to determine adsorption characteristics of thin films, deposited on piezoelectric quartz crystal (PQC) and on microchannels. The procedures consist only in an injection of small quantities (28 mg of n-hexane and/or 0.29 mg of 2-propanol) into the system or microstructure.…”

“…Little difference was found for the deposition rates, probably due to a similar deposition mechanism. Although some oxidation or reduction of oxygenated species occur, the polymerization probably depends mainly on the removal of hydrogen from CH bond and the formation of carbon-carbon bond [19,20,22]. The high relative intensity of oxygenated species, noticed for almost all films, is probably due to the low power used during depositions that avoids the breakdown of monomer molecules.…”

“…Although all films are hydrophilic, there are two trends: (a) bigger water contact angle was found for films with double layers and (b) lower contact angles were related to closed chamber mode deposition. Double layers might lead to island formation [20,22] that partially exposes the hydrophobic HMDS thin film and, without a doubt, increases the angle. Closed chamber mode allows surface reactions after the plasma shut off that might change wettability.…”

“…Plasma deposited thin films have been used on many applications, such as surface protection and/or modification [16][17][18] and recently organic thin films were tested for adsorption of volatile organic 0925 compounds (VOCs). These films were obtained using monomers in a large range of polarity: ethyl ether, ethyl or methyl acetate, acetone, acetaldehyde and 2-propanol [19][20][21][22][23] and using 40 kHz power supply.…”