The space charge distribution, conductivity characteristic and breakdown strength of cross-linked polyethylene (XLPE) insulation materials under DC voltage are the key issues in the development of HVDC cable materials. The introduction of deep charge traps in polyolefin matrix by appropriately grafting polar groups onto polyolefin molecular chains can efficiently improve the dielectric performances of HVDC cable insulation materials. It is of great significance for developing HVDC cable materials to study the modifying schemes and mechanisms of chemically grafting polar molecules in polyethylene. With the thermochemical method based on peroxide initiated radical reaction, three kinds of polar molecules acrylic acid (AA), acrylate chloroacetate (CAAE) and maleic anhydride (MAH) were individually grafted onto XLPE molecular chains. It is indicated by infrared spectra that AA, CAAE and MAH molecules have been successfully grafted onto polyethylene molecular chains in the crosslinking networks of XLPE by radical addition reactions on their unsaturated double-bonds. Space charge distribution, charge trap characteristics, DC conductance and breakdown strength of the modified XLPE materials were analyzed to elucidate the effective mechanisms of polar-groups on the comprehensive amelioration in dielectric performances. The study found that grafting polar molecules introduces deep charge traps in XLPE, which remarkably impedes the electrode injection and internal transport of charge carriers under high electric field, thus alleviating the space charge accumulation inside, abating conductance currents and increasing breakdown strengths. Among them, MAH graft-modified XLPE material shows relatively superior comprehensive properties.

The Multi-gap Resistive Plate Chamber (MRPC) has been used in many high energy physics and nuclear experiments in the last decade, such as ALICE [1] and STAR [2]. Normally, the MRPC is built with commercial floating glass (bulk resistivity ρ≈ 1012Ω· cm), which limits the rate capability to less than 1 kHz/cm2. In modern high energy physics, with the increase of colliders beam energy and luminosity, the rate capability of MRPC has to be enhanced accordingly. One normal way is to decrease the bulk resistivity ρ of the resistive plate, as the low resistive glass developed by Tsinghua University for the CBM experiment [3]. Alternatively, the surface of the electrode is also a possible path for the neutralization of the avalanche charges. Recently, we managed to carry this method out by coating a Diamond-Like-Carbon (DLC) layer on the surface of the floating glass. The DLC layer, realized by the magnetron sputtering method, has very good physical and chemical stability. The demanded surface resistivity can be achieved easily. A series of DLC-coated glasses with different resistivity has been tested in our lab. We have also made some MRPC prototypes and tested them with cosmic rays. Some preliminar results, including the operating current, the efficiency and the time resolution, have been achieved. More research is ongoing to improve the design and performance of this new method of increasing the rate capability of MRPC.

In recent years, fluorescent quantum rods (QRs) receive much attention because of their properties of emitting specific wavelength polarized light with narrow full width at half maximum (FWHM). Therefore, QRs are usually aligned on devices, such as light emitting diodes, laser, and liquid crystal display (LCD), as a polarizer. In order to emit the light with a high degree of polarization (DOP), QRs need to be controlled and aligned almost along one direction on large‐scaled devices. However, most of the proposed effective alignment approaches cannot be applied to a large area. Hence, we firstly propose the contact ink‐jet printing (CIJP) method to align CdSe/CdS core/shell QRs. With the ink being printed, the QRs can move driven by ink flowing. Eventually, the QRs will be aligned along the printed trajectories and become a film with DOP of more than 40%. Furthermore, CIJP can realize arbitrarily large area fabrication without reducing DOP value. In the future, this method can be utilized to print on large‐scaled substrates directly to fabricate polarized optoelectronic devices, and further applied to LCD backlights and optical lenses.