Enhancing Slide Electrification by Polarization of Electret Materials

Sliding electrification is the spontaneous charge separation when water droplet moves over the hydrophobic surface ^{1, 2}. Sliding electrification has been explored for various fluoropolymers (PFOTS, PTFE etc.)³ and non-fluorinated polymers⁴. For fluoropolymers and non-fluoropolymers surfaces a highest drop charge of approximately ~2 nC has been reported⁵. Fluoropolymers are electret materials, which can be pre-charged by polarization. However, slide electrification effects were not investigated for defined polarization states. Using a defined polarization state offers the possibility to increase the efficiency of charge separation significantly. Therefore, we investigated how pre-charged hydrophobic surfaces impact sliding electrification. The hydrophobic surface has been used in this study that is Cyclic Transparent Optical Polymer (CYTOP) fluoropolymer. CYTOP has the capability to store the negative charge for months⁶. We applied an intense electric field of -6 MV/m for 15 min to a ~500 – 600 nm thick CYTOP film. For this field strength causes a corona discharge where dipoles orient near the surface^{7, 8}. The advancing and receding contact angles of pre-charged CYTOP (PCC) were 85° and 65° respectively, for non-charged CYTOP (NCC) film 112° and 102° respectively. Consequently, contact angle hysteresis (CAH) was observed around 10° and 20° for NCC and PCC surface, respectively. Sliding electrification experiments revealed a drop charge of approximately ~1.2 nC corresponding to a drop discharge current of ~6 µA on for the NCC surface. However, the drop charge increased on the PCC surface to ~8.3 nC that corresponds to a drop discharge current of ~100 µA drop current. Therefore, using pre-charged CYTOP surface results in an eight-fold higher drop charge than any other reported slide electrification charge for 45 µL volume drops. The drastic increment in drop charge shows the discernible impact of pre-charge CYTOP surface. I will discuss how slide electrification can be used to power energy-autonomous sensing systems.<br/><br/><b>Refrences</b><br/>1. Yatsuzuka, K.; Mizuno, Y.; Asano, K., Electrification phenomena of pure water droplets dripping and sliding on a polymer surface. <i>Journal of Electrostatics </i><b>1994,</b> <i>32</i> (2), 157-171.<br/>2. Li, X.; Bista, P.; Stetten, A. Z.; Bonart, H.; Schür, M. T.; Hardt, S.; Bodziony, F.; Marschall, H.; Saal, A.; Deng, X.; Berger, R.; Weber, S. A. L.; Butt, H.-J., Spontaneous charging affects the motion of sliding drops. <i>Nat. Phys. </i><b>2022,</b> <i>18</i> (6), 713-719.<br/>3. Nauruzbayeva, J.; Sun, Z.; Gallo, A.; Ibrahim, M.; Santamarina, J. C.; Mishra, H., Electrification at water–hydrophobe interfaces. <i>Nature Communications </i><b>2020,</b> <i>11</i> (1), 5285.<br/>4. Li, S.; Bista, P.; Weber, S. A. L.; Kappl, M.; Butt, H.-J., Spontaneous Charging of Drops on Lubricant-Infused Surfaces. <i>Langmuir </i><b>2022,</b> <i>38</i> (41), 12610-12616.<br/>5. Stetten, A. Z.; Golovko, D. S.; Weber, S. A. L.; Butt, H.-J., Slide electrification: charging of surfaces by moving water drops. <i>Soft Matter </i><b>2019,</b> <i>15</i> (43), 8667-8679.<br/>6. Shalini; Arya, D. S.; Beigh, N. T.; Kumar, S.; Mudgal, R.; Singh, P.; Muduli, P. K.; Mallick, D.; Goswami, A. In <i>Energy Harvesting From Water Droplet Motion Confined On A Hydrophobic-Hydrophilic Stripped Surface</i>, 2022 IEEE 35th International Conference on Micro Electro Mechanical Systems Conference (MEMS), 9-13 Jan. 2022; 2022; pp 943-946.<br/>7. Sessler, G. M., Electrets: Recent developments. <i>Journal of Electrostatics </i><b>2001,</b> <i>51-52</i>, 137-145.<br/>8. Li, X.; Wang, Y.; Xu, M.; Shi, Y.; Wang, H.; Yang, X.; Ying, H.; Zhang, Q., Polymer electrets and their applications. <i>J. Appl. Polym. Sci. </i><b>2021,</b> <i>138</i> (19), 50406.<br/>&lt;!--[if supportFields]&gt;&lt;span lang=EN-US style='font-size:12.0pt;line-height: 107%;font-family:"Times New Roman",serif;mso-fareast-font-family:Aptos; mso-fareast-theme-font:minor-latin;mso-font-kerning:0pt;mso-ansi-language:EN-US; mso-fareast-language:EN-US;mso-bidi-language:AR-SA'&gt;&lt;span style='mso-element: field-end'&gt;&lt;/span&gt;&lt;/span&gt;&lt;![endif]--&gt; &lt;!--![endif]----&gt;