Self-healing Superhydrophobic SMEP/PDMS@ZnO@SiO2 Coating and its Anticorrosion Performance
摘要: 本文针对环氧树脂基类超疏水防腐涂层的物理损伤修复速度较慢，并结合不锈钢金属长期处于高湿高盐等环境下高效防腐与保护的实际应用需求，以微晶蜡强化的环氧树脂基自修复涂层(SMEP)为底层，以超疏水材料PDMS@ZnO@SiO2(PZS)为表层，基于双层设计制备了一种较快修复机械损伤、不锈钢持久防腐的自修复超疏水涂层SMEP/PDMS@ZnO@SiO2(SMEP/PZS)，并着重对其修复前后SMEP/PZS涂层的润湿性、耐蚀性及其自修复与防腐机制等进行了深入探讨。结果表明，SMEP/PZS涂层具有良好的超疏水性及自清洁等相关性能，其超疏水性随着低表面能物质PFDTMS含量增加而增强，水接触角、滚动角最佳可达157.6和2.6°。其次，SMEP/PZS涂层有较快的自修复能力，将该机械模拟的受损涂层于85℃下在20 min较短时间内进行修复，其最佳机械划痕由45 μm缩小至1.0 μm，修复率达97.8%。此外，SMEP/PZS涂层表现良好的耐蚀性，且将修复后的该涂层置于3.5wt%NaCl溶液中浸泡14天后，其耐腐蚀性接近于原始涂层。将SMEP/PZS涂层涂覆在不锈钢基底上，在3.5wt%NaCl溶液中所测点蚀电位Eb与裸不锈钢的相比正移近10倍，维钝电流密度Ip下降2个数量级，对304不锈钢基底具有相对更为持久的防腐与保护。最后，进一步探讨了SMEP/PZS涂层的自修复与防腐蚀机制。Abstract: In this paper, based on the two-layer design, a self-healing superhydrophobic coating SMEP/PDMS@ZnO@SiO2 (SMEP/PZS) that could quickly repair physical damages and durably corrosion resistance of stainless steel was prepared. Aiming to solve the slow physical damage repair of epoxy-based superhydrophobic anti-corrosion coatings, and inegrate with the practical application requirements of high efficiency anticorrosion and protection of stainless steel in high humidity and high salt environment for a long time. The double-layer coating was designed by combination of a self-healing epoxy-based coating reinforced by microcrystalline wax (SMEP) and a superhydrophobic material PDMS@ZnO@SiO2 (PZS). Furthermore, the wettability, corrosion resistance, self-healing and corrosion resistance mechanism of SMEP/PZS coating before and after repairing were discussed in detail. The results show that SMEP/PZS coating has excellent superhydrophobicity and self-cleaning properties, and its superhydrophobicity increases with the increase of PFDTMS content, its optimal water contact angle and rolling angle are157.6 and 2.6°. Secondly, SMEP/PZS coating has a faster self-healing ability, the best mechanical scratches of SMEP/PZS coating are reduced from 45 μm to 1.0 μm in a shorter time of 20 min at 85℃, and the repair rate reaches 97.8%. In addition, the SMEP/PZS coating shows good corrosion resistance, and after the repaired coating is immersed in 3.5wt% NaCl solution for 14 d, its corrosion resistance is closed to the original coating. When the SMEP/PZS coating is coated on the stainless steel substrate, the pitting corrosion potential Eb measured in 3.5wt% NaCl solution has increased by nearly 10 times compared with that of the bare stainless steel, and the passive current density Ip has decreased by 2 orders of magnitude, showing relatively longer corrosion resistance and protection for 304 stainless steel substrate. Finally, the self-healing and anti-corrosion mechanism of SMEP/PZS coating is further discussed.
图 1 SMEP/PDMS@ZnO@SiO2(SMEP/PZS)涂层的制备过程示意图
Figure 1. The preparation process of SMEP/PDMS@ZnO@SiO2(SMEP/PZS) coating
PDMS—Polydimethylsiloxane; PFDTMS—Perfluorodecyltrimethoxysilane; NGDE—Neopentyl glycol diglycidyl ether; DGEBA—Bisphenol A diglycidyl ether; D-230—Polyetheramine D-230; EA—Ethyl acetate.
图 3 表面形貌，SMEP涂层(a)；PZS涂层：(b)7wt% PFDTMS，(c)21wt% PFDTMS，(d)42wt% PFDTMS；SMEP/PZS涂层：(e)7wt% PFDTMS，(f)21wt% PFDTMS，(g)42wt% PFDTMS
Figure 3. SEM images of SMEP coating (a); PZS coating with (b) 7wt% PFDTMS, (c) 21wt% PFDTMS, (d) 42wt% PFDTMS; SMEP/PZS coating with (e) 7wt% PFDTMS, (f) 21wt% PFDTMS, (g) 42wt% PFDTMS
图 5 裸不锈钢、PZS、SMEP及SMEP/PZS涂层的交流阻抗谱，(a)Nyquist图；(b)阻抗模量曲线；(c)相位角曲线；(d)不同PFDTMS含量SMEP/PZS涂层的阻抗模量曲线
Figure 5. Ac impedance spectroscopy of bare stainless steel, PZS, SMEP and SMEP/PZS coatings, (a) Nyquist diagram; (b) impedance modulus curve; (c) phase angle curve; (d) impedance modulus curve of SMEP/PZS with different content of PFDTMS.
Z', Z"—Nyquist diagram represent the real and imaginary parts of the impedance
图 7 修复前后涂层的表面形貌，SMEP涂层(a1、a2)；SMEP/PZS涂层：(b1、b2)7wt% PFDTMS，(c1、c2)21wt% PFDTMS，(d1、d2)42wt% PFDTMS。注：脚标1为修复前，脚标2为修复后
Figure 7. SEM images of the coating before and after healing, SMEP coating (a1、a2); SMEP/PZS coating with (b1、b2) 7wt% PFDTMS, (c1、c2) 21wt% PFDTMS, (d1、d2) 42wt% PFDTMS. Note: Pin 1 is before repair, and pin 2 is after repair
图 9 修复后涂层于3.5wt% NaCl溶液浸泡1 day，7 days，14 days后的阻抗模量曲线，SMEP(a)；SMEP-ZPS：wt%(b)7wt%PFDTMS，(c)21wt%PFDTMS，(d)42wt% PFDTMS
Figure 9. The impedance modulus curve of coating after healing and immersion in 3.5wt% NaCl solution for 1 day、7 days、14 days, SMEP(a); SMEP/PZS coating with (b) 7wt% PFDTMS, (c) 21wt% PFDTMS, (d) 42wt% PFDTMS
表 1 PDMS@ZnO@SiO2(PZS)和SMEP/PDMS@ZnO@SiO2(SMEP/PZS)涂层表面的水接触角及滚动角
Table 1. Contact angle and rolling angle of PDMS@ZnO@SiO2(PZS) and SMEP/PDMS@ZnO@SiO2(SMEP/PZS) coatings
PZS SMEP/PZS 0wt% 7wt% 21wt% 42wt% 0wt% 7wt% 21wt% 42wt% Unsoaked CA/(°) 151.8 154.1 156.7 159.4 150.9 153.6 155.9 157.6 SA/(°) 6.9 4.6 3.6 1.8 7.8 5.3 3.9 2.6 Soaked 12 h CA/(°) 149.1 152.1 154.5 155.8 148.9 151.9 153.8 155.4 SA/(°) 12.6 6.5 5.0 4.1 13 6.4 5.2 4.4 Note: CA stands for static water contact angle, SA stands for roll angle.
表 2 由裸不锈钢、分别涂覆PZS、SMEP及SMEP/PZS涂层的不锈钢基底的极化曲线所得相关评价参数
Table 2. The related evaluation parameters were obtained from the polarization curve of bare stainless steel and stainless steel substrates coated with PZS, SMEP and SMEP/PZS
Coating Ecorr/V Icorr/A Eb/V Ip/A 304 stainless steel −0.752 9.728×10-5 0.0562 1.020×10-4 PZS −0.406 1.458×10-6 −0.04 7.476×10-6 SMEP −0.269 6.042×10-7 0.0455 6.783×10-6 SMEP/PZS −0.160 5.283×10-8 0.312 6.672×10-6 Notes: Ecorr stand for self-corrosion potential, Icorr stand for self-corrosion current density, Eb stand for pitting potential, Ip stand for passive current density.
表 3 修复前后不同含量PFDTMS的SMEP/PZS涂层的接触角及滚动角
Table 3. Contact angle and rolling angle of SMEP/PZS coating with different content of PFDTMS before and after healing
CA/(°) SA/(°) 7 wt% 21 wt% 42 wt% 7 wt% 21 wt% 42 wt% Original 153.6 155.9 157.6 5.3 4.9 2.6 Scratched 147 145.4 146.4 16.6 17.8 16.1 Healed 152.4 153.8 155.3 5.9 5.8 4.9
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