Abstract:

Objective Infrared (IR) stealth is essential in modern military. With the rapid development of infrared detection technology, effectively hiding targets and rendering them invisible to thermal infrared detectors have been great challenges. Infrared stealth effect is affected by both temperature and infrared emissivity, but most of the previous studies focused on a single factor, which limits the effectiveness of the products. In order to achieve better infrared stealth effect, a composite fiber membrane material was prepared with low infrared emissivity on the outer surface and temperature control function inside.

Method The continuous electrospinning method was used to prepare the composite fiber membrane with the effect of controlling temperature and moderating infrared emissivity. By controlling the mass ratio of polyethylene glycol(PEG1000 and PEG4000) and the amount of nano-iron particles, the fiber membrane with different phase change temperature and infrared emissivity was obtained. The mass ratio between PEG4000 and PEG1000 was 2∶1, 3∶2,1∶1 and 2∶3, and nano-iron particles accounted for 10%, 20%, and 30% of the PAN quality, respectively. The apparent morphology, chemical and phase structure, thermal properties and infrared emissivity of the composite fiber membranes were studied. The infrared stealth properties of composites were investigated.

Results The surface of pure PAN fibers is smooth and the diameter distribution is uniform. The phase change fibers doped with polyethylene glycol became rough and wrinkled, and some fibers exhibited a fine groove-like morphology, which is, however, regular without showing polymer intorface separation. The composite fiber was well formed and showed certain dimensional stability. The infrared spectrum demonstrated that PAN(polyacrylonitrile) and PEG(Polyethylene glycol) have good binding and compatibility, which is consistent with the results of SEM. With the different mass ratios of PEG4000 and PEG1000, the phase transition temperature was between 31.5-40 ℃, with a regulation range of about 10 ℃. The phase change enthalpy and phase change temperature of fiber membrane PCM1(the mass ratio between PEG4000 and PEG1000 is 2∶1) changed less more than 2 % after 40 thermal cycles, indicating good energy storage stability. The temperature control effect of phase change fiber membranes with different thicknesses was analyzed. The phase change fiber membrane PCM1 with 0.9 mm and 1.2 mm thicknesses was placed on a 55 ℃ hot stage. When the surface temperature of PCM1 reached about 40 ℃, the heating rate was significantly slowed down, which was consistent with its phase change endothermic temperature. The temperature rise rate of 0.9 mm and 1.2 mm thick PCM1 fiber membranes became very slow after 6 min, and the actual temperature difference with the surface of the hot stage was 7 ℃ and 12 ℃, respectively.This is because the relatively thick fiber membrane means more phase change materials, which can absorb more heat and form better temperature control effect. The infrared emissivity of PAN, 0.1Fe/PCM1,0.2Fe/PCM1 and 0.3Fe/PCM1(nano-iron accounts for 0%, 10%, 20% and 30% of the PAN quality, respectively) were 0.9,0.82,0.69 and 0.75, respectively. The infrared emissivity of the fiber membrane decreased after the addition of nano-iron, and reached the lowest when the doping amount was 20 %. In the absence of sunlight, it is equivalent to the environment of grass or rock (infrared emissivity 0.65-0.75). By placing 0.2Fe/PCM1 on the hot stage, it can be seen from the infrared thermal imaging that it is similar to the radiation color of the environment and has infrared stealth effect.

Conclusion Through multi-component design and structural construction, a composite material with low infrared emissivity on the outer surface and internal insulation and temperature control functions has been prepared. The synergistic effect achieves the infrared camouflage function of the material, and to some extent overcomes the limitation of achieving infrared camouflage from a single aspect. It is hoped that it can provide a new way of thinking for the research of infrared stealth materials.

Key words: polyacrylonitrile, polyethylene glycol, iron nanoparticle, infrared stealth, electrostatic spinning, composite cellulosic membrane, phase-transition temperature, infrared emissivity