Electret Coatings

The formation of electret coatings on flat surfaces in fact evokes no problems. They are formed on polarization of polymer coatings on curvilinear surfaces of complex shapes. 

The spreading motive force corresponds to the sorption capacity of the coating. The sorption intensity of electret coatings is less than that of the reference ones [15], therefore spreading over them is slower. 

The sorption characteristics of electret coatings are described in Fig. 3.14 [15]. Sorption of liquids by electret coatings is seen to be noticeably lower than by reference ones (charge density 10 -10 C/cm ). This difference increases 

Information on diffusive permeability of electret coatings is presented in Table 3.3. Based on these results, an analytical dependence between the liquid mass absorbed by the coating and the polarizing charge value has been derived [16]. 

The described advantages of electret polymer coatings have not been called for until recently chiefly due to the lack of information and inaccessibility of electret techniques. It is taken for granted today that the electrically polarized state is a natural physical state of polymer dielectrics. The realization of merits that are intrinsic to polymer coatings may open new 

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This suggests that resistance of the hardware in corrosion-active media can be raised substantially using electret coatings with the electret charge. 

Fig. 7.22 Thermally stimulated current spectra of FEP electret foils (aluminium, coated on one side) immediately after polarisation. The heating rate was 4 C min"1. Reproduced with permission of the American Institute of Physics from Sessler and West (1971).

PVDF was patented in 1948 and commercialized by Pennsalt in 1962. It is a semi-crystalline polymer with = -56 to -35°C, 50 % crystallinity, and = 160-180°C. PVDF has been blended mainly with PMMA [Lin and Burks, 1993]. The blends are suitable for the use as stable electrets or weather-resistant architectural coatings. Nearly 25 wt% of PVDF consumption is in... 

Fig. 3.14. Sorption of diethylene glycol vapors by non-polarized (1, 3) and electret (2, 4) coatings of polyvinyl butyral. Temperature (1, 2) 50 (3, 4) 30°C...

Fig. 3.20. A scheme for a combined polymer antirust coating. (1) metal substrate, (2) passivating layer, (3) a layer of organic metal, (4) a layer containing corrosion inhibitors, (5) electret polymer layer...

Fig. 4.8. Mass wear rate (/m) dependence on ESCD (Oe/) value and sign for electret PE coatings. Friction regime p = 0.5 MPa v = 0.5 m/s [47]...

Lo and Tai (2008) developed an electret generator without tefliers. The rotor can slide freely relative to the stator, and then induced charges on the electrodes vary with toe position of the rotor. With a rotor coated with parylene... 

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