Advantage 5 of the Six Major Advantages of Electrostatic Flocking
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Anisotropy refers to the directional dependency of physical or chemical properties.[64] Large quantities of isotropic materials exhibit electrical, thermal, and wettability characteristics that are independent of direction.[65] However, in some applications, anisotropic modulation of these properties is required. The ori ented surface of the electrostatic flock construction gives the opportunity for targeted improvements in electrical, thermal, and wettability characteristics.
Owing to their vertical alignment and direct surface contact, flocking fibers serve as bridges between the electrolyte, active material, and current collector in supercapacitors or electrodes, functioning as active materials or current collectors (Figure a). These advantages facilitate exchange and reduces ionic transport resistance.[66] The flocked nanostructures provide excellent ohmic contact with the electrode materials and the substrate, enabling efficient electron transport and electrolyte accessibility.[67,68] Furthermore, the vertically ordered structure of the flocked fibers provides a plethora of ion for exchange and electron transport “highways” for the active materials deposited on their surfaces (Figure b), effectively promoting the performance characteristics of the active materials and enhancing conductivity perpendicular to the substrate.[67,69] All of above factors result in a oriented and straight-forward conductivity along the direction of the fibers.
Since certain materials, such as h-BN and carbon fiber, have exceptional thermal conductivity in a single direction, the unique isotropic alignment of these materials rather than random distribution can be made through electrostatic flocking.[18,20] Electrostatic flocking offers a method for arranging fillers in a specific manner, creating anisotropic surfaces that align the fill ers with their direction of maximum thermal conductivity, providing more efficient thermal paths and maximizing the directional thermal conductivity of the material.[20,22] The flexible epoxy resin film electrostatically flocked with boron nitride platelets (BN/epoxy) exhibited the fastest temperature response,reaching 92.3 °C in just 250.4s (Figure c), and the λ enhance ment efficiency of flocked BN/epoxy to epoxy resin refers to 18.6% higher than that of random BN/epoxy (Figure d).[18] Also, electrostatic flocking materials with fibers aligned in the direction of heat transfer demonstrate superior thermal conductivity compared to those arranged in other directions. Uetani et al.[22] fabricated a series of vertically aligned carbon fiber (VACF) scaffolds with different alignments and revealed that the through-plane thermal conductivity exhibited a significant dependency on the degree of alignment, dropping sharply from 21 to 0.4WmK 1forthecomposites derived from nearly planardistributed carbon fibers (Figure e).
The dense fiber clusters formed by electrostatic flocking on the vertical substrate surface create micropores arranged perpendicular to the substrate. This structure allows liquids such as oil to be rapidly attracted and transported in the vertical direction through capillary action,[59,62,70] which can improve vertically oriented wettability. Additionally, when fibers are modeled as cylinders, viscous damping along the cylinder’s flow is lower compared to viscous damping perpendicular to the cylinder’s axis.[71] This indicates that the transport capacity of cylindrical fibers along the fiber axis is greater than that perpendicular to the fiber axis. In the case of electrostatic flocking being applied to the high-speed steel surface, as more oil diffuses into the grooves, the capillary force of the pores at the upper part of the fibers attracts the oil upward and shows a slow and then fast infiltration process.[62] First, the oil slowly wets the bottom of the groove (Figure f,i).[62] Subsequently, as wetting proceeds, capillary forces in the pores of the upper layers of the fibers accelerate the upward wetting of the oil (Figure f,ii).[62] Under intermolecular forces, oil droplets merge by closing gaps between them, causing the upper oillayer to coalesce into a continuous film that enhances lateral penetration (Figure f,iii).[62] The superior performance of the oil storage capacity of the flocked surface experiments (Figure g) can also prove the merit of directional wetting in a sideway. Currently, an increasing number of studies reported that electrostatic flocking can be produced to absorb and transport oil in high-speed steel surface[59–62,72–77] or heavy oil clean-up.[78]
a) Electrode and current collector interface morphology (i) and surface morphology of the SAPN electrode after cycling (ii); reprinted with permission. [68] Copyright © 2016 Elsevier B.V.
b) Schematic diagram of the principle of directional conductivity via electrostatic alignment of flakes; reprinted with permission. [66] Copyright © 2022 John Wiley & Sons Ltd.
c) Infrared thermal images during the heating and cooling process under a laser point source for epoxy resin, random BN/epoxy, and aligned BN/epoxy composite films; the tested composite thickness is about 200 μm; reprinted with permission. [18] Copyright © 2023 Elsevier Ltd.
d) Comparison of thermal conductivity enhancement for composites compared to pure epoxy resin; reprinted with permission. [18] Copyright © 2023 Elsevier Ltd.
e) Relationship between fiber orientation angle and thermal conductivity for three types of composites, with insets showing optical micrographs of the corresponding fiber-aligned scaffolds; reprinted with permission. [22] Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
f) Schematic diagram of groove penetration in a flocked layer, showing directional wetting along the fiber direction; reprinted with permission. [62] Copyright © 2022 Elsevier B.V.
g) Liquid storage phenomenon on an inclined surface; reprinted with permission. [59] Copyright © 2023 The Author(s), under exclusive licence to Springer Nature Limited (Springer Nature, London).
References:
[18] Li, X., Xu, Q., Lei, Z., Chen, Z., Ceramics International, 2023, Vol. 49.
[20] Sun, Y., Wang, S., Li, M., Gu, Y., Zhang, Z., Materials Characterization, 2018, Vol. 144.
[22] Uetani, K., Ata, S., Tomonoh, S., Yamada, T., Yumura, M., Hata, K., Advanced Materials, 2014, Vol. 26.
[59] [Author(s) names not provided in original text], [Journal Title not provided in original text], 2023. (Note: Original caption cites [59] but it's not in the provided reference list)
[62] Li, J., Feng, K., Zhao, H., Wang, Z., Meng, Z., Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2022, Vol. 651.
[65] Wan, J., Song, J., Yang, Z., Ke, C., Jia, C., Xu, R., Dai, J., Zhu, M., Xu, L., Chen, C., Wang, Y., Wang, Y., Xi, Z., Lai, X., Li, Y., Yang, B., Hu, L., Advanced Materials, 2017, Vol. 29.
[66] Li, M., Qin, L., Ou, K., Xiong, Z., Zheng, H., Sun, Y., International Journal of Energy Research, 2022, Vol. 46.
[67] Xu, C., Li, Z., Yang, C., Zou, P., Xie, B., Lin, Z., Zhang, Z., Li, B., Kang, F., Huang, C., Advanced Materials, 2016, Vol. 28.
[68] Cho, G., Jeong, J., Choi, M., Noh, J., Cho, K., Kim, J., Ahn, H., Nam, T., Kim, K., Surface and Coatings Technology, 2017, Vol. 326. (Note: "G.乔" likely corresponds to "G. Cho" or similar, "J.郑" to "J. Jeong", etc. Adjusted based on common Korean surname romanizations. Check original source for precise spelling.)
[69] Pikul, J. H., Zhang, H. G., Cho, J., Braun, P. V., King, W. P., Nature Communications, 2013, Vol. 4.
[70] Lu, D., Ni, J., Zhang, Z., Feng, K., Materials, 2024, Vol. 17, 4166.
[71] Brücker, C., Journal of Physics: Condensed Matter, 2011, Vol. 23.
[72] Perez, P. J., Garcia, A., Yang, J., Axinte, D., International Journal of Mechanical Sciences, 2022, Vol. 222. (Note: Names romanized based on common spellings for the likely origins: P. Javier, G. Andres -> P.J. Perez, A. Garcia?; Y. Jian -> J. Yang; A. Dragos -> D. Axinte? Check original source for precise spelling.)
[77] Yang, Y., Zhang, L., Wang, J., Wang, X., Duan, L., Wang, N., Xiao, F., Xie, Y., Zhao, J., ACS Applied Materials & Interfaces, 2018, Vol. 10.
[78] Yang, X., Tian, Y., Zhou, R., Xia, F., Gong, Y., Zhang, C., Ji, F., Liu, L., Li, F., Zhang, R., Yu, J., Gao, T., Advanced Fiber Materials, 2024, Vol. 6.
Excerpt from the paper "Electrostatic Flocking: Reborn to Embrace Multifunctional Applications"