Aromatic polyurea films of a few hundred nanometer thickness were prepared by vapor deposition polymerization of the monomers 4,4′-diaminodiphenylmethane and 4,4′-diphenylmethane-diisocyanate. Piezoelectric activity was observed after poling the films under an electric field of 100 MV/m at 210 °C for 10 min. The piezoelectric stress constant (polarization/strain) remains constant at about 15 mC/m2 over the temperature range from −50 to 200 °C. The multilayer film produced by the alternate deposition of polyurea layers and aluminum electrodes exhibited a response proportional to the number of layers. The residual polarization caused by alignment of the dipoles of the urea bond is believed to be the origin of the effect.

We show the existence of a new class of astrophysical objects where the self-gravity of the dust is balanced by the force arising from shielded electric fields on the charged dust. The problem of equilibrium dust clouds is formulated in terms of an equation of hydrostatic force balance together with an equation of state. Because of the dust charge reduction at high dust density, the adiabatic index reduces from two to zero. This gives rise to a mass limit M AS for the maximum dust mass that can be supported against gravitational collapse by these fields. If the total mass M D of the dust in the interstellar cloud exceeds M AS , the dust collapses, while in the case M D < M AS , equilibrium may be achieved. The physics of the mass limit is similar to the Chandrasekhar's mass limit for compact objects, such as white dwarfs and neutron stars.

A new method for preparing the polymer films directly in the reduced atmosphere has been developed. In this process the polymerization can be carried out through depositing the component monomer vapors. Both pyromellitic dianhydride and 4,4′-diaminodiphenyl ether (oxydianiline) were evaporated at a molar ratio in terms of stoichiometry by controlling the heating power for each evaporation source. From the infrared absorption spectrum observation, it was found that the as-deposited film was the mixture of the polyamic acid and both nonreacted monomers. After having been heated to 200 °C for 60 min, the deposited film was finally transformed into the polyimide film through the condensation reaction. The obtained polyimide film had good adhesion to the glass and metal substrate and showed excellent chemical resistance, heat resistance, and electrical insulation characteristics. By selecting the appropriate combination of monomers, other polymer films could be obtained through the vacuum deposition polymerization process.

Thin films of aromatic polyurea were prepared by simultaneous deposition of 4,4'-diamino diphenylmethane (MDA) and 4,4'-diphenylmethane diisocyanate (MDI) on a polyimide film substrate. By changing the evaporation temperature of the monomers, the monomer molar ratio of MDA to MDI of the deposited film was varied to yield MDA-rich, balanced, and MDI-rich films. After poling, the balanced films exhibited the maximum values of pyroelectric and piezoelectric constants, which were stable up to 200°C. Elemental analysis confirmed that oligomers consisting of about five monomers were present in as-deposited films. In the balanced films, an exothermic peak appeared at about 110°C in the first run of DSC measurements and the IR absorption peak due to isocyanate groups disappeared after heat treatment. These results suggest that during the poling process polymerization of oligomers, which forms polar urea bonds, takes place at about 110°C under a high electric field. The large residual polarization thus produced leads to high pyroelectric and piezoelectric activities.

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