The laser intensity modulation method (LIMM), developed by Lang in the early eighties, is a useful technique for determining the spatial polarization and/or space charge distributions in pyroelectric and/or piezoelectric materials, for instance in thin polymer electret films. The advantage of the LIMM is the high spatial resolution near the irradiated side. Therefore, we introduced the logarithmic spatial grid distribution into the deconvolution process. For the first time the self-consistency method developed by Honerkamp and Weese is applied to the deconvolution program with respect to LIMM. Using multilayer systems with known spatial distributions our new equipment is tested with regard to providing reasonable results as well as the deconvolution program to represent the known spatial distributions.

In the present paper, heat wave (LIMM) and pressure pulse (LIPP) measurements of the space-charge distributions in electron-beam irradiated Teflon FEP ( thick) are reported. The space-charge profiles obtained by the two methods are compared over the whole sample thickness. From the LIMM with the back surface heat sink, the space-charge distribution can be found from the surface of illumination up to at least half of the sample thickness. For the position of the bulk space charge, the heat wave and LIPP response results agree with each other to within . By using LIMM, an additional negative charge layer near the surface is found if the electron-beam irradiation is carried out through the metallized sample surface.

No abstract

Poly(oxyethylene)-bl~k-poock-poly(oxypropylene~block-poly(oxyethylene) copolymers were applied as nonionic surfactants in styrene emulsion polymerization. The clouding phenomenon of the surfactant in the aqueous phase and the resulting characteristic partition of the block copolymer between aqueous and organic phase result b, two particularities of this system compared with classical emulsion polymerization: i) bimodal particle size distribution, and ii) unusual dependence of reaction rate on temperature.

The transient pyroelectric response of a dielectric film on a substrate is used to determine both the electricfield profile across the film and its thermal properties. The response is a convolution of the field and temperature profile. A closed-form expression for the transient temperature profile is obtained for a generic model in terms of thermal parameters. This expression allows analysis of the pyroelectric response using an iterative procedure consisting of deconvolution and variation of thermal parameters. Tikhonov regularization is used in the deconvolution with a Honerkamp-Weese self-consistent regularization parameter. Simulations show that, at least in the cases tested, the electric-field profile, the thermal diffusivity and conductivity ͑and thus the heat capacity, which is their ratio͒, and the thermal resistance of the dielectric/substrate interface can be determined. Experiments on polyimide films adhered to substrates unambiguously reveal bound negative charge within a small depth of the free surface of virgin samples and also weaker, broader charge distributions injected from the substrate in samples under an applied voltage. The analysis resolves both sharp and broad features and gives thermal properties characteristic of the near-surface region, suggesting that the heat capacity may be significantly higher in this region than in the bulk.