Dielectric spectra of polarization in conducting ...

DIELECTRIC SPECTRA OF POLARIZATION IN CONDUCTING POLYMER THIN FILMS John Texter‡, Dennis J. Savage§, and Brian K. Brady† ‡Strider

Research Corporation, Rochester, NY 14610-2246, Kodak Company, Rochester, NY 14650, and †General Motors Research and Development, Global Alternative Propulsion Center, Honeoye Falls, NY 14472 §Eastman

Introduction The formation and discharge of electrostatic charge during the manufacture and utilization of photographic film and paper can produce a variety of problems. These problems include dust accumulation and associated coating defect formation. Irregular fog patterns or “static” marks from the untoward discharge of accumulated charge can result from static charge built up during film winding and unwinding, during transport through coating, slitting, and spooling machines, and during removal of film from light-tight packaging. Such static accumulation can generally be controlled and dissipated by incorporating antistatic layers that are electrically conductive. Antistatic layers have been formulated with various electrically conductive materials. Ionic conductors have been widely used, but conductivity in such cases is often highly dependent on relative humidity. Electronic conductors have also been employed. Very small (1010.5

ε2, σ2

Compositional details are summarized in Table 1, where the surface electrical resistance (SER) measurements and the loss peak frequencies are also tabulated. All of the spectra exhibit a high-frequency hump or peak at about 2 x 105 Hz. This low-intensity loss peak is a material property of the PET and has been assigned to the so-called α transition in PET.6 Essentially identical spectra were obtained for PET controls having no conductive thin film layer. The two spectra obtained with binder A constitute a series in thin film thickness, where the binder/ECP ratio is unity. The resistance decreases as the film thickness increases. The effect of the binder A is to dilute the ECP and to increase the film resistance by over an order of magnitude. The effects on the loss peak frequency appear even greater. The binder B coatings at weight ratios of 70/30 and 50/50, together with the 0/100 coating, exhibit over a 3 decade decrease in loss peak frequency as dilution with binder imposes over a three-fold variation in ECP weight fraction. This behavior is reminiscent of a percolation phenomenon induced by volume fraction variations of the conducting phase (ECP) .7 The loss peak frequencies and the SER, on a log-log basis, exhibit an inverse linear relationship, where the loss peak frequency increases as the film conductivity increases (SER decreases). This behavior may be understood in terms attributed by Dukhin and Shilov8 to Maxwell, or by an equivalent circuit analysis,9 for a heterogeneous two-layer dielectric such as illustrated in Figure 3. In such a case where we have an insulating layer, such as the PET layer in this situation, and a conducting layer from the ECP thin films, the dielectric loss peak frequency may be shown to be proportional to the thin film conductivity (σ):9 fmax ∝ σ. These pronounced loss peaks correspond to Maxwell-Wagner polarization at the ECP/PET interface.

Poly(EDOP/SS) - binder

d1 ≈ 100 µm

d2 ≈ 400 nm

Figure 3. Two-layer heterogeneous dielectric composed of ECP thin film [poly(EDOP/SS)] coated on PET support, where the support layer is much thicker than the ECP thin film. Acknowledgment. Tonya Binga is gratefully acknowledged for her assistance with the dielectric spectroscopy measurements.

References (1) (2) (3) (4) (5) (6) (7) (8) (9)

Trevoy, D., U.S. Patent 3,245,833 (1966). Guestaux, C., U.S. Patent 4,203,769 (1980). Anderson, C.C.; Kestner, D.E.; Lewis, M.A.; Optiz, G.R., U.S. Patent 5,006,451 (1991). Savage, D.J.; Schell, B.A.; Brady B.K., U.S. Patent 5,665,498 (1997). Merz, A.; Schropp, R.; Dötterl, E., Synthesis 1995, 795. Dobbertin, J.; Hensel, A.; Schick, C., J. Thermal Anal. 1996, 47, 1027. Doyle, W.T., J. Appl. Phys. 1978, 49, 795. Dukhin, S.S.; Shilov, V.N., Dielectric phenomena and the double layer in disperse systems and polyelectrolytes (D. Lederman, Trans), Halsted Press, New York, 1974; pp./ 22-25. Texter J.; Lelental, M., Langmuir 1999, 15, 654.

Polymer Preprints 2000, 41(1), 37