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A new mechanism leading to hole injection into insulating polymers under normal operating fields is presented. In general, it is unlikely that holes can be injected into large band-gap insulating materials under normal operating fields less than 1 MV cm−1, particularly for materials that are not in the form of thin films. However, insulating polymers consist of a large amount of various unavoidable ionic impurities, so ionic conduction plays an important role in their electrical properties. The presence of such ions modifies the field distribution in the material with the tendency of enhancing the field toward the anode, thus increasing the probability for hole tunneling from the anode to the material. The appearance of positive space charge near the anode after a prolonged period of electrical stressing, as observed by many investigators, may be considered as the experimental evidence of the mechanism. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1864–1867, 2003

Among the oldest of professions are Medicine (the art and science of healing) and Teaching. both of which. in the earliest of times. were accorded the respectability of nobility. Medicine continues to be a highly regarded profession. Many factors contribute in maintaining this notion of nobility. not the least of which is the sentiment attached to the sanctity of human life.

A new optical technique for the determination of spatial distributions of the thickness and the optical constants of thin films is proposed. This technique is simple and nondestructive involving mainly an ellipsometer and a coherent light source, and no contact to the thin-film samples is required. A theoretical estimation indicates that this technique may provide a spatial resolution close to the diffraction-limited resolution under certain conditions. Possible applications of this technique are also discussed.

On the principle that the spatial distribution of the refractive index produced by a small applied temperature difference is changed due to an electromechanical force created by the field resulting from the spatial variation of the dielectric constant, the electric field distributions in a dielectric system can be determined using the schlieren method. Some experimental results for benzene and n-hexane between two spherical electrodes obtained with this method show the essential features predicted from the space charge effects. This method can be used to study electric field and space charge distributions under both steady and transient conditions.

The structure of ethylene-vinyl-acetate (EVA) copolymers depends strongly on the comp9sition of E (ethylene) and VA (vinyl-acetate). With various compositions in VA:E ratio in weight, the results show that both the density and the melt index increase, while the molecular weight, the melt viscosity and the degree of crystallinity decrease with increasing VA:E ratio in EVA copolymers. This reflects that both the ethylene sequence length and the activation energy of fluidity decrease with increasing VA content. The change of the structure of EVA copolymers is directly correlated with the change of the mechanical and dielectric properties of this material. The peak values of the dielectric constant and the dielectric loss in the dielectric relaxation temperature characteristics increase, while the activation energy of polarization and the dielectric breakdown strength decrease with increasing VA:E ratio. Other mechanical properties, such as the tensile strength and the environment stress cracking, also correspondingly decrease as the molecular weight and the ethylene sequence length decrease due to the increase of VA content in EVA copolymers.

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