No abstract

Statistical mechanical averages of vectors and tensors characterizing the configurations of polymethylene chains with n = 5-200 bonds have been calculated, these quantities being expressed in the internal reference frame attached to the first two bonds. Specifically, the persistence vector a ==

No abstract

Electrical conduction phenomena in polyimide (Kapton) films were studied with particular attention devoted to the separation of interface and bulk phenomena. The measurements were carried out with a variety of methods in the temperature range of 50 to 270 °C at electrical fields of 104 to 6×105 V/cm and at time intervals of up to 2×104 s after voltage application. Biased, two-side metallized samples yield, after sufficiently long voltage application, interface-controlled steady-state currents described by Schottky injection, modified by space-charge layers in the vicinity of the electrodes. The effective work function for aluminum-polyimide is estimated to be 1.7 eV in the temperature range between 100 and 270 °C. A distinct dependence of these currents on electrode material is observed. Bulk phenomena were studied on one-side metallized samples subject to positive-corona charge injection. At temperatures below 200 °C, significantly larger currents than those for biased, two-side metallized samples were observed. The current-voltage characteristics are ohmic at low fields and space-charge limited at high fields. From these data, trap modulated mobilities for positive carriers of 4×10−12 cm2/V s at 50 °C and 10−9 cm2/V s at 200 °C, ohmic bulk conductivities of 10−16 (Ω cm)−1 at 100 °C and 10−14 (Ω cm)−1 at 200 °C and an intrinsic carrier density of 5×1013 cm−3 independent of temperature are obtained. Activation energies for the mobility are between 0.2 and 0.8 eV for the temperature range between 50 and 200 °C.

We report on the direct evidence in real space of the crystal−amorphous interphase in a lamellar semicrystalline polymer, poly(ethylene terephthalate) (PET). This evidence was obtained by the TEM observation of the compositional variation of (stained) PET segments in the boundary of an isolated lamellar stack in a binary blend of semicrystalline PET with amorphous poly(ether imide). The lamellar morphology exhibited by the TEM image of a stained lamellar stack was also investigated in detail, in terms of the thickness distributions of lamellar crystallites and noncrystalline interlamellar layers. The validity of employing our TEM imaging method through differential staining of PET segments was then ascertained by comparing the power spectral density obtained from the TEM data with the measured small-angle X-ray scattering profile from semicrystalline PET samples. Compared with this lamellar morphology, the thickness of the observed crystal−amorphous interphase at the boundary of the lamellar crystallites and (mixed) random melts is even greater than the thickness of the noncrystalline interlamellar layer of PET. This striking result may be attributed to the rigid aromatic groups in the PET chain backbone which prohibit the occurrence of tight chain folding. Accordingly, the entire noncrystalline interlamellar region of aromatic semicrystalline polymers may be regarded as the interphase, devoid of truly random amorphous phase.