A series of poly(vinylidene fluoride) (PVDF)/ poly(vinyl alcohol) (PVA) composite films with different ratios were prepared by electrospinning. Because of the intermolecular interaction force, the highest thermal conductivity of the above film is 2.434 W m −1 K −1 , which is about 60% higher than that of the pure PVDF film without a strong intermolecular interaction force. Infrared and wide-angle X-ray diffraction (WXAD) proved that PVDF as a thermal bridge enhances the internal interaction force and makes the internal structure more regular. The laser method shows that the film with strong intermolecular interaction has higher thermal diffusivity. Using molecular dynamics to explore the thermal expansion rate of the system, it is found that the intermolecular interaction force and the thermal bridge can effectively inhibit the activity of the molecular chain and reduce its free volume. After an in-depth study of the influence of the intermolecular interaction force and the thermal bridge on polymers, it is found that electrospinning can conveniently and effectively improve the ordering of the polymer structure. Integration of the electrospinning method and intermolecular interaction leads to the remarkable improvement of intrinsic thermal conductivity for polymer blends.

At present, the situation of air pollution is still serious, and research on air filtration is still crucial. For the nanofiber air filtration membrane, the diameter, porosity, tensile strength, and hydrophilicity of the nanofiber will affect the filtration performance and stability. In this paper, based on the far-field electrospinning process and the performance effect mechanism of the stacked structure fiber membrane, nanofiber membrane was prepared by selecting the environmental protection, degradable and pollution-free natural polysaccharide biopolymer pullulan, and polyvinylidene fluoride polymer with strong hydrophobicity and high impact strength. By combining two kinds of fiber membranes with different fiber diameter and porosity, a three-layer composite nanofiber membrane with better hydrophobicity, higher tensile strength, smaller fiber diameter, and better filtration performance was prepared. Performance characterization showed that this three-layer composite nanofiber membrane had excellent air permeability and filtration efficiency, and the filtration efficiency of particles above PM 2.5 reached 99.9%. This study also provides important reference values for the preparation of high-efficiency composite nanofiber filtration membrane.

In 3D packaging memory devices, solder joints are critical links between the chip and the printed circuit board (PCB). Under severe working conditions, cracks inevitably occur due to thermal shock. If cracks grow in the solder joint, the chip will be disconnected with the PCB, causing its function failure. In this paper, the reliability of solder joints under thermal shock are evaluated for 3D packaging memory devices by means of the SEM and finite element analysis. As microscopically studied by the SEM, it is found out that the main failure mechanism of solder joints in such test is the thermal fatigue failure of solder joints. Finite element analysis shows that cracks are caused by the accumulation of plastic work and creep strain. The initiation and growth of cracks are mainly influenced by the inelastic strain accumulation. The trends of cracks are influenced by the difference between the coefficient of thermal expansion (CTE) of epoxy resin and that of the chip.

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