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Low‐frequency ac conduction and dielectric relaxation in vinyl chloride:vinyl acetate copolymers

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5 Author(s)
Singh, Ramadhar ; National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110012, India ; Panwar, V.S. ; Tandon, R.P. ; Gupta, N.P.
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ac conductivity σ(ω), dielectric constant ϵ’, and loss ϵ‘ of vinyl chloride:vinyl acetate (VC:VAc) copolymers having 3%, 10%, and 17% VAc content (by weight) have been measured in the temperature range 77–410 K and in the frequency range 50 Hz–100 kHz. At low temperatures up to 250 K, the ac conductivity can be expressed by σ(ω)=Aωs, where the slope s is close to unity and its value decreases with the increase in temperature. The dielectric constant in this temperature region shows a very weak frequency and temperature dependence. At temperatures above 300 K, the ac conductivity shows a strong temperature dependence; however, in this temperature region the dielectric constant shows a strong frequency dispersion. The measured dielectric loss as a function of temperature reveals the β1, the β2, and the α relaxations. The β1 relaxation is associated with the movement of the more flexible side group dipoles and the β2 relaxation is due to the movement of rigidly attached side group dipoles, whereas the α relaxation is attributed to the segmental motion of the main chain of the copolymer. Both the latter relaxations seem to be long range in nature with distribution of relaxation times associated with the cooperative motion. The mechanism of conduction in the low‐ and high‐temperature regions have been discussed in light of existing theoretical models.

Published in:

Journal of Applied Physics  (Volume:72 ,  Issue: 8 )