The processes leading to very long lifetimes of implanted electric charge are discussed. A model assuming a competition between the rate of current carrier generation in activation processes, and the rate of carrier annihilation on electrodes and by free, implanted charge was considered. The discussed processes lead to a very pronounced decrease in electric conductivity, and in consequence to long lifetimes of implanted charge, in agreement with experimental data. The important feature of our model is that exponential decay of charge takes place only for short times-hours or days for polymers. For the longer periods-hundreds or thousands of years in the case of Teflon films-a linear decay is predicted. The importance of the shape of a dielectric plate and the unusual stability of thin electrets are also discussed. ͓S0163-1829͑99͒12915-1͔

Many methods for the determination of the order parameter in nematic liquid crystals are known. However, most of them are not applicable to cholesteric and smectic phases. Therefore, experimental data on the order parameter in cholesteric and smectic phases are hardly available. To determine the orientational order parameter S we exploited the de Gennes observation, that any anisotropic physical quantity may be a measure of orientational ordering in nematic mesophase. The order parameter can be calculated directly from a macroscopic quantity measured in the experiment. From this idea we developed a simple method for the determination of the order parameter based on birefringence measurements, which can be applied for nematic, cholesteric, and smectic phases. A precise and simple method for measurement of the optical birefringence is described. An approximate empirical formula is applied for normalization of the optical birefringence similar to that used by Haller for polarizabilities. The results are in excellent agreement with the literature data. We proved that in the case of optical anisotropy the order parameter is equal within AE 1% to the one evaluated from polarizability anisotropy. Thus, the discussion concerning the local field can be omitted. Using the described method we determined the orientational order parameter in various mesophases.

The results of studies on the dielectric polarization for the whole range of concentrations of 2-pyrrolidinone ( -butyrolactam) in benzene as a function of temperature (20-50 °C) at 1,5 kHz are presented. The results were interpreted by assuming a model of monomer + dimer + tetramer equilibrium. The formation constants for dimers (K2) and tetramers (K4) as well as the molar enthalpies for hydrogen bonds N-H-0=C in these associates (-2 = 15.2 kJ/mol and -AH4 = 17.4 kJ/mol) were calculated.