In this paper, crosslinked polyethylene-polystyrene (XLPE-PS) composites with different degrees of crosslinking were fabricated by using different crosslinking agent contents and their direct current (DC) breakdown performance at 30~90 °C was investigated. Results show that with the increase of the degree of crosslinking, the crystallinity of XLPE-PS composites decreases gradually, but their DC breakdown strength demonstrates an increasing trend at 30~90 °C and the enhancement also increases with the rise of temperature. And as the degree of crosslinking increases, the elastic modulus of XLPE-PS composites is reduced and the loss tangent peak temperature decreases but the peak shifts to a lower value, which reveals the suppression of the relaxation process for crystallites. It is believed that high DC breakdown strength with good temperature stability for XLPE-PS composites with a larger degree of crosslinking is attributable to the presence of PS and suppression in the formation of crystallites due to crosslinking.

ever-increasing requirement for high energy density, [1][2][3][4] especially when incorporating with further material modification through nanocomposites, [7][8][9][10] blending, [11][12][13][14][15][16] laminated structure, [17][18][19][20][21] cross-linking, [22,23] and so on.Nevertheless, the state-of-the-art PVDF-based ferroelectric polymer usually exhibits mediocre temperature stability in energy storage performance, which cannot fully satisfy the applications at elevated temperature caused by the energy consumption or nearby heat sources. [24][25][26] These polymers commonly possess glass transition temperature (T g ) far below room temperature (as shown in Table S1, Supporting Information), which helps to enhance the energy density but sacrifices temperature stability. The molecular motion in ferroelectric polymers can be activated above T g , which promotes polar molecules orientation under external stimulus evidenced by a sudden increase of permittivity at T g . [23,27] Consequently, ultrahigh energy density (about 4-35 J cm −3 ) for PVDF-based polymers has always been reported at room temperature above T g . [1][2][3] On the other hand, low T g is detrimental to temperature stability of energy storage in PVDF showing dramatical degradation at elevated temperatures. Because rubbery-state amorphous region above T g , which manifests itself as loose chains with increased free volume, becomes vulnerable to temperature rise. [25,26,28] Recent investigations even point out that high-T g non-ferroelectric polymers can maintain an energy density around 0.5-1.8 J cm −3 up to a fairly high temperature. [25,26,29] Nonetheless, for ferroelectric polymers, it remains a considerable challenge to achieve high energy storage performance at the elevated temperature.In this work, we propose to design a strategy for stabilizing high energy density of ferroelectric polymer (PVDF) over a wide temperature range by blending with a miscible high-T g polymer (polymethyl methacrylate [PMMA]). The blending material forms a alternating lamellar structure consisting of high-polarization crystalline regions and mixed amorphous regions. It is found that this special morphology can induce a spatial confinement effect of chain mobility and structural change at elevated temperatures. Accordingly, the associated Thermal stability of polymer structure is a key to achieve stable energy density at elevated temperature for ferroelectric-polymer-based capacitors. Here, a poly (vinylidene fluoride) / polymethyl methacrylate (PMMA) blend with a stabilized spherulite structure displaying steady energy density around 7.8-9.8 J cm −3 across the temperature range up to 70 °C is reported, which outperforms most neat ferroelectric polymers at elevated temperature. The microstructure of the blend observed by atomic force microscopy exhibits an alternating lamellar structure (crystalline/mixed amorphous layers) within spherulites, which might be rationalized by PMMA being gradually expelled from the spherulite and finally staying between PVDF lamellae ...

In this paper, we propose a method on improving direct current (DC) dielectric performance by designing a polystyrene (PS) pinning crosslinked polyethylene (XLPE) for the application of insulation materials on high voltage direct current (HVDC) extruded cable. Electrical experimental results show that the addition of PS (1–5 phr, parts per hundreds of resin) can significantly reduce DC conductivity and increase DC breakdown strength of XLPE in the test temperature range of 30–90 °C. Microstructure investigation shows PS distributed as particles could participate in the formation of a crosslinking network with the help of a crosslinking agent, thus forming a polymer pinning structure at the interface between XLPE and PS. It is believed that such a special design strengthens the structure of XLPE, which leads to the improved DC dielectric performance at elevated temperatures. Our findings may contribute a new solution for developing HVDC cable insulation materials.

The stiffness and the topography of the substrate at the cell–substrate interface are two key properties influencing cell behavior. In this paper, atomic force acoustic microscopy (AFAM) is used to investigate the influence of substrate stiffness and substrate topography on the responses of L929 fibroblasts. This combined nondestructive technique is able to characterize materials at high lateral resolution. To produce substrates of tunable stiffness and topography, we imprint nanostripe patterns on undeveloped and developed SU-8 photoresist films using electron-beam lithography (EBL). Elastic deformations of the substrate surfaces and the cells are revealed by AFAM. Our results show that AFAM is capable of imaging surface elastic deformations. By immunofluorescence experiments, we find that the L929 cells significantly elongate on the patterned stiffness substrate, whereas the elasticity of the pattern has only little effect on the spreading of the L929 cells. The influence of the topography pattern on the cell alignment and morphology is even more pronounced leading to an arrangement of the cells along the nanostripe pattern. Our method is useful for the quantitative characterization of cell–substrate interactions and provides guidance for the tissue regeneration therapy in biomedicine.