Several important issues and thinking about engineering dielectrics

With the development of studies in engineering dielectrics, more and more unaccepted questions arise. To provide peer reviews for these questions, we propose several important issues and thinking. The concept of nanometric dielectrics was firstly proposed by T J Lewis in 1994, and it has become the research focus of engineering dielectrics since 2003. However, from the point of view of the research results for more than 20 years, the original intention of the author and some recently-proposed nanostructured dielectrics, we believe that nanometric dielectrics should be renamed nanodielectric composites, and be redefined in accordance with low dimensional physics. The specific meaning of Lewis interface and Tanaka interface is analyzed, hard/soft interface of nano polymeric composites is proposed, new concepts of structural complexity, uncertainty and mutability are described, and the scale and physical and chemical properties of hard and soft surfaces are analyzed. New thoughts are inspired from the perspective of Einstein reductionism, emergent phenomena of P W Anderson, and scientific prediction of R P Feynmann. Constraints of existent conditions of space charge limited current (SCLC) are studied, and hierarchical levels of its self-structure, complex interface, electrode contact, concomitant electronic and ionic conductivity and other factors in polymers or their composites have serious impacts on SCLC. It is proposed that SCLC is not solely determined by carriers which are the same as injected carriers in the transition from ohmic region to high field region, i.e., electrode injection SCLC region. In particular, the contribution of ionic conductivity to the current in low and high field region is of close scrutiny when measurement conditions are determined. Therefore, the main features and distinction methods of ionic and electronic conductivity are listed. In view of pulse related space charge measurement methods, especially pulsed electroacoustic (PEA) method has been mainly adopted in the world, advantages and disadvantages of PEA, and the method for verifying the accuracy and repeatability of measurement results are proposed. According to the features of polymer structure, a pressure stimulated current (PSC) device should be built up for distinguishing space charges derived from concentration gradient of electrons, ions, and dipoles to compensate the serious shortcomings of PEA measurements.