Doped Polystyrene Films Research Articles

Electron conduction in fe‐doped polystyrene films

AbstractThe DC electrical conductivity of pure and Fe3+‐doped polystyrene films has been studied at various bias field strengths in the temperature range 304–392K. Doped films showed increased conductivity compared with undoped films up to 0.5% dopant concentration; beyond this concentration there was a decrease in the conductivity. The increase in conductivity for lower doping concentrations (0.25% and 0.5%) is attributed to the formation of charge transfer complexes. The decrease in the electrical conductivity and the increase in the activation energy at more than 0.5% dopant concentration is due to the formation of molecular aggregates. For undoped films the activation energies in the low temperature region were found to be higher than those at higher temperatures. Also, with increasing bias field strength, the activation energies showed a decrease at all temperatures studied. It is suggested, on the basis of the magnitudes of the activation energies, that electronic conduction is the dominant charge transport mechanism both at low and high temperatures.

Photo-sensitized degradation of CCl 4-doped polystyrene in the solid phase

The photo-degradation of carbon tetrachloride (CCl 4)-doped polystyrene film has been investigated by ultraviolet (uv) and Fourier transform infrared (FTIR) spectroscopic techniques and by gel and viscosity measurements. On photo-irradiation of CCl 4-doped polystyrene film, the amount of oxygenated products and unsaturation increased with the concentration of carbon tetrachloride up to 5 mol%. Changes in gel fraction and number of chain scissions showed a similar trend to those of the amount of oxygenated products and unsaturation. These experimental results show that the degradation of polystyrene is photo-sensitized by added carbon tetrachloride. A possible mechanism for the photo-degradation of CCl 4-doped polystyrene is proposed.

Photo-electret studies of pure and doped polystyrene films

The photoelectret properties of pure and acrylic acid (AA) doped polystyrene (PS) films formed by an isothermal immersion technique have been studied. The photoelectrets were formed by simultaneous application of u.v. radiation for a short time period (2–10 min) and d.c. electric field (3–18 V). The depolarization current was obtained by reilluminating the photoelectret with the same radiation. It is found that the photo depolarization current increases with polarizing voltage and is greater for the doped samples than for the undoped samples, prepared under identical conditions. The current increases with the dopant concentration and with duration of polarization. The total charge, found by integrating the depolarization current-time curve of doped photoelectrets, tends to saturation at a certain voltage value. Doped PS gives better photoelectrets.

Delayed specific luminescence of aromatic scintillators

A modified expression for the delayed specific luminescence of organic scintillators as a function of the incident-particle linear energy transfer is presented. Theoretical curves thus produced show a good fit to the experimental results obtained with doped polystyrene films irradiated with α particles of energy ranging from 1 to 5 MeV. The adjusted value for the bimolecular interaction parameter B T for the different concentrations of solute in the films gives consistency to the assumptions made.

Spectroscopic studies of undoped and doped polystyrene films

Spectroscopic (i.r., u.v.) studies of undoped polystyrene and that doped with Acrylic Acid films (30μ thick), prepared by isothermal immersion technique, have been reported. It is found that in the case of i.r. spectra an additional absorption peak appears near 1420cm−1, whereas those present near 1300 and 980cm−1, as shoulders in the undoped sample, appear as sharp peaks in the doped samples. In the region 3300–2500cm−1 a broadening appears in the doped films which increases with the dopant concentration. In the case of u.v. spectra, out of four absorption regions present in the undoped films two bands merge and only three appear in the doped ones. The u.v. absoption increases with the dopant concentration. These results have been explained on the basis of a charge transfer complex formation due to the interaction between the dopant and the polymer matrix.

Thermally stimulated discharge currents from pyrene-doped polystyrene films

Pyrene was mixed with polystyrene (PS) in different molar concentrations in the range 0.2–12 mol.% and thermally stimulated discharge (TSD) current spectra of the doped PS films were studied for various dopant concentrations, polarizing fields and forming temperatures. Unpolarized films were observed to give a peak at 95°C. The TSD current peak in the main relaxation region of PS shifts to the lower temperature side of the spectrum with increasing concentration of the dopant. The strong dependence of space charge polarization on the dopant concentration and the forming temperature is assigned to an increase in the conductivity of the polymer.

Thermally stimulated discharge current studies in copper phthalocyanine ‐ doped polystyrene films

AbstractTo improve the electret characteristics, TSD current studies of copper phthalocyanine ‐ doped polystyrene films of about 20 microns thickness have been made as a function of doping concentration, poling temperature and field. Generally the thermograms observed exhibit α and ρ peaks. The activation energy is found to decrease as the concentration of the dopant in the polymer is increased. It is established that keeping the forming field constant and by increasing the concentration of the dopant, the same polarisation can be obtained at a lower poling temperature. A Maxwell‐Wagner two‐phase model with space ‐ charge build‐up seems to provide a possible mechanism for the polarisation.

Photo‐polarisation in pure and doped polystyrene

AbstractDepolarisation currents have been measured of the photo‐electrets of pure and copperphthalocyanine doped polystyrene films using UV‐radiation. A hyperbolic decay law is observed suggesting bimolecular recombination process. Doped films show strong saturation with the applied field supporting a trap filling mechanism.

TSD Study of Pure and Chloranil Doped Polystyrene Films Grown from Solutions

Three peaks, namely, β, α, and ρ peaks, have been observed in the TSD spectra of commercial polystyrene (PS) at about 338, 368, and 418 K respectively. Their origin is due respectively to the trapping of charge carriers by the particular atoms or molecules pressent in the amorphous regions of polystyrene, to the segmental motion of main chains, and to the accumulation of space charges at the crystalline and amorphous interfaces. Doping of polystyrene with chloranil [electron affinity 1.4 eV (2.24×10−19 J)] has been found to form charge-transfer complexes. This probably involves three mechanisms: increase in the mobility of charge carriers, reduction in the trapping sites for charges, and provision of conductive path ways for them through the crystalline-amorphous interfaces.