Article pubs.acs.org/Langmuir
Unexpected and Unusual Triboelectrification Behavior of Polymer Films Containing Carboxyl Group Yuji Hiraga, Yudai Teramoto, Nobukazu Miyagawa, and Katsuyoshi Hoshino* Graduate School of Advanced Integrated Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan S Supporting Information *
ABSTRACT: The triboelectrification behavior of polymer films when in contact with iron carrier beads was investigated using a homemade special instrument which can control relative humidity under a nitrogen atmosphere. The films showed a large humidity-dependent charging behavior; the charge amount increases with the ambient humidity in the range of a few percent RH to ca. 60% RH. This dependence is explained in terms of the model based on the water charging during the friction and the penetration of the positively charged water into the film. However, it was found that the humidity dependence is significantly depressed by the doping of carboxylic acids into the film or by the introduction of a carboxyl group in the polymer backbone. This depression is again explained by the above charged-water penetration model in which carboxylate ions trap the positively charged water on the film surface.
1. INTRODUCTION When two materials come in contact or are rubbed together, the transfer of an electric charge occurs between the two materials, and the net electric charge of one side is negative and that of the other side is positive. The fundamental understanding of this phenomenon is still insufficient and remains vague though this contact/triboelectrification behavior is extremely simple from the viewpoint of the process.1−4 For instance, there is a question of “what are the charge carrier species, electrons, ions, or charged material pieces?”5−12 Furthermore, there is another question about the mechanism of the charge transfer.13,14 There is also a question about the effect of the ambient atmosphere on the electrification,15−17 and this issue should have a close relation with the former two questions. The contact/triboelectrification is an important phenomenon utilized for toner charging in electrophotography.18−20 If the above-mentioned problems are elucidated, it becomes possible to intentionally control the amount and polarity of the toner charge, leading to the reproducible charging of the toner particles and the formation of the reproducible fine toner images. We have been studying the triboelectrification between the insulating polymer films and the carrier beads (iron powder), which are the major components of toners, in a humiditycontrolled nitrogen atmosphere, and have been specifically examining the effect of humidity on the triboelectrification of the polymer films.21−23 Through the examination, we have found many examples in which the amount of tribocharges increased in a negative direction along with an increase in the humidity (in the humidity range below ca. 60% RH). In order to explain this behavior, which is seemingly different from our © XXXX American Chemical Society
ordinary experiences, we proposed a charged-water penetration (CWP) model.23 In this CWP model, it is assumed that positively charged water is formed at the interface between the polymer and the carrier beads during their friction24,25 and that the generated positively charged water penetrates into the polymer bulk. Hence, the penetrated positively charged water forms a positive space charge in the polymer film and changes the electronic states of the polymer. This change in the electronic states causes a significant effect on the amount and direction of electron transfer between these two materials, and therefore, the polarity and charge amount of the polymer are partially determined by the ambient humidity condition (refer to section 3). That is, in the CWP model, it is assumed that ionic species participate in the electrification process of water and that the electron transfer participates in the charging process. However, sufficient data to support the CWP model are still not available. In this study, the triboelectrification behaviors of a polymer film doped with carboxylic acids and a polymer film having a carboxyl group in the polymer backbone were examined. This examination led to the finding that the triboelectrification behaviors of these films were only slightly influenced by the humidity in contrast to those of the films not containing a carboxyl group. These findings will be again explained on the basis of the CWP model. Received: March 12, 2013 Revised: May 21, 2013
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dx.doi.org/10.1021/la400926q | Langmuir XXXX, XXX, XXX−XXX
Langmuir
Article
PMMA and poly(MMA-co-MA) solutions were prepared by dissolving the polymers (2.0 g) in a toluene/2-butanone mixture (1/1, 8 mL). Before applying a coating of the films, aluminum substrates were degreased by sonication in acetone and dried. All of the films were uniform with no visible defects and holes in the surface. The carboxylic acid compounds used as dopants are shown in Chart 1 which involves 4-aminobenzoic acid (abbreviated as ABA, Kanto
2. EXPERIMENTAL SECTION 2.1. Tribocharging Apparatus. Our apparatus used for the triboelectric charging experiments12,21−23 consists of a cylindrical sample holder (∼76 mm diamter), a magnet roll (∼16 mm diameter) with a sleeve covered with iron carrier beads (∼110 μm in diameter, no resin coating), and a cam for adjusting the gap formed between the sample surface and the sleeve (Figure 1A). Tribocharging experiments
Chart 1. Chemical Structures of Dopant Molecules
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