基于液状PDMS的共价键合型动态双疏表面及其自清洁功能

黄颖芬

基于液状PDMS的共价键合型动态双疏表面及其自清洁功能

黄颖芬

（泉州医学高等专科学校 药学院，福建 泉州 362011）

通过简便的方法在惰性基底上构建具有稳定动态双疏性能和自清洁功能的表面。利用非化学计量比的硅橡胶前体表面具有的硅氢键和单乙烯基封端聚二甲基硅氧烷之间的氢化硅烷化反应，在惰性不锈钢基底上制得透明、平滑、无氟、稳定的基于液状PDMS的共价键合型动态双疏表面CBDOS（Covalently-Bonded Dynamically-Omniphobic Surface）。通过ATR-FTIR和XPS表征表面的化学组成，通过AFM和FE-SEM分析表面形貌，通过液滴形状分析仪测定表面的接触角CA值、滑动角SA值和接触角滞后CAH值。分析证实液状PDMS已被成功键合在CBDOS表面，且表面具有纳米级粗糙度，均方根粗糙度q仅为0.964 nm。同时，表面具有卓越的动态双疏性能和良好的储存稳定性，水的SA值为2.20°、CAH值为1.75°，正十六烷的SA值为7.33°、CAH值为7.34°。这使CBDOS对极性或非极性、相溶或不相溶、水溶性或油溶性的污染物都展现出良好的自清洁功能。CBDOS极端均匀平滑的表面形貌及其上单端共价键合的液状PDMS所具有的高度移动性和柔韧性，使其获得卓越的动态双疏性能和自清洁功能。本方法简便，条件温和，对环境无污染，并可拓展应用于各类基底。同时，由于液状PDMS是共价键合在材料表面，可有效增强动态双疏表面的稳定性。

聚二甲基硅氧烷；液状聚合物；氢化硅烷化；共价键合；动态双疏；自清洁

材料表面的抗润湿行为是一种重要的界面现象，因其在自清洁[1-6]、防污染[7-8]、防腐蚀[9-13]、防覆冰[13-17]、减阻[18-20]等诸多领域应用前景广阔，近年来，吸引了越来越多研究人员的关注和重视。早期对材料表面抗润湿性能的研究主要是以接触角CA（Contact Angle）为评判标准，即在静态条件下，以CA值90°作为亲液和疏液表面的界线。考虑到界面间分子的相互作用，该界线现已降低至65°[21-22]。研究还发现，将CA值相同的材料表面同时倾斜同样的角度，有的表面会使液滴滚落或滑落，而有的表面则使液滴粘附。因此，要全面地评价材料的抗润湿性能，单纯考察静态接触角是不充分的，还应分析表面的动态抗润湿行为。相关研究报道中将材料表面的疏液性能分为静态和动态疏液性能，并以滑动角SA（Sliding Angle）和接触角滞后CAH（Contact Angle Hysteresis）作为表征表面动态疏液性能的关键指标[23-24]。材料表面的SA值和CAH值越小，表明其对液滴的粘附力越小，这样的表面越有利于液滴滚落或滑落，从而实现动态疏液和自清洁等功能[25-26]。据文献报道，当极性和非极性的液滴在材料表面的SA值和CAH值都小于10°时，一般就认为该表面具备卓越的动态双疏性能[23,27-29]。目前，针对动态双疏表面的研究还较少。

弹尾虫[30-33]和猪笼草[34-35]为了适应恶劣的生存环境，进化出了具有动态双疏性能的表皮结构和口缘区结构。受它们的启发，研究人员开发了2种实现表面动态双疏性能的策略。一种是构建具有特定微纳米粗糙结构，特别是凹角几何结构的表面[36-40]。这种策略的难点在于其所需构建的拓扑结构复杂、精细，因此对仪器、技术和成本的要求较高。同时，当表面遭受外力作用时，多尺度微观结构易被破坏，从而失去疏液性能，因此该策略不适于规模化推广应用。另一种策略是在微纳米多孔结构表面灌注润滑液，用低表面能的液体替代多孔结构中的气体，形成光滑、均一的抗润湿表面。该方法虽然克服了多级粗糙结构易磨损、不耐压等弊端[41-45]，但是润滑液只是通过弱的毛细作用力保持在底层多孔结构中，因此常常会因为蒸发或液滴挟带等原因而使润滑液损失，以致失去动态双疏性能。同时，为了尽量减小材料的表面能，进而实现优秀的抗润湿性能，上述2种策略大多需要修饰或灌注含氟化合物，这将潜在一定的污染性。

为了克服上述缺陷，研究人员提出了一种独特的新策略，即将液状聚合物共价键合到材料表面，利用表面平滑均匀的形貌以及液状聚合物高度的移动性和柔韧性实现卓越的动态双疏性能[46-48]。聚二甲基硅氧烷（PDMS）具有低表面能、低玻璃化转变温度，同时主链上的—Si—O—Si—重复单元赋予其良好的移动性和柔韧性，因此在室温下仍然保持优异的熔融状态，可以看作液状聚合物，是现阶段构建此类表面最适宜的聚合物之一[23,49]。此外，该策略将液状聚合物共价键合到基底表面，可有效增强动态抗润湿表面的稳定性。但是，已有文献报道中的共价键合方式很有限，大多是将液状聚合物直接键合在硅片等具备反应活性的基底表面[23,27,47]，这将大大限制该方法在普通基底材料上的应用。因此，有必要探索一种可以在惰性基底表面实现该策略的键合方法。本研究以非化学计量比的Sylgard 184液体硅橡胶为前体，通过其表面具有的硅氢键和单乙烯基封端PDMS之间的氢化硅烷化反应，在惰性不锈钢基底表面形成了透明、平滑、无氟、稳定的共价键合型动态双疏表面CBDOS（Covalently-Bonded Dynamically-Omniphobic Surface）。

1 试验

1.1 动态双疏表面的制备

将Sylgard 184（美国Dow Corning）A、B组分按质量比（1∶10或1∶2）混合，在顶置式机械搅拌器（德国IKA）作用下以1800 r/min搅拌15 min，随后抽真空直到没有明显气泡。将足量的混合物滴加于预处理（首先用砂纸打磨不锈钢片表面，随后清洗干净，再置于丙酮中超声，最后用纯化水充分洗净，并烘干）后的2 cm×2 cm不锈钢片，置于台式匀胶机（北京赛德凯斯KW-4B型）上，以300 r/min旋涂10 s，再将转速增大到800 r/min旋涂40 s。处理后的样品再一次真空脱泡，随后加热硫化，分别得到2种质量比的硅橡胶。其中，质量比为1∶10的硅橡胶标记为S184，质量比为1∶2的硅橡胶标记为pre-CBDOS。

将单乙烯基封端聚二甲基硅氧烷（MVT-PDMS，江苏科幸VM500）和铂金催化剂（江苏科幸CAT- Pt015）混合均匀，再将pre-CBDOS浸没于该混匀体系中，于50 ℃恒温箱中反应5 h。随后取出，竖直静置24 h后，依次用丙酮、乙醇及纯化水充分清洗样品，直至在洗涤溶剂中检测不到MVT-PDMS，以除去表面残留的未键合的MVT-PDMS。最后，将样品于50 ℃下干燥数小时，即制得基于液状PDMS的共价键合型动态双疏表面，标记为CBDOS。

1.2 表征与性能测试

1）通过傅里叶红外光谱仪（美国Thermo-Fisher Nicolet 5700型）ATR法分析不锈钢基底、S184、pre-CBDOS和CBDOS中基团的变化。

2）通过X射线光电子能谱仪（美国Thermo- Fisher Escalab 250Xi型）分析pre-CBDOS和CBDOS的表面原子组成。

3）通过场发射扫描电子显微镜（日本电子株式会社JSM-7500F型）分析CBDOS的表面形貌。用导电胶带将待测样品固定于样品台上，使用离子溅射仪（中镜科仪）将导电金膜沉积于样品表面。

4）通过原子力显微镜（美国Veeco Nanoscopy ⅢA型）分析不锈钢片和CBDOS的表面形貌，并计算均方根粗糙度。工作模式：轻敲；探针型号：FESP-V2；扫描范围：2 μm×2 μm。

5）通过液滴形状分析仪（德国KRUSS DSA 25型）分析、测定不锈钢片和CBDOS表面的接触角CA值、滑动角SA值、前进角A、后退角R和接触角滞后CAH值，测试液体为极性的纯化水和非极性的正十六烷。CA值测试：将2 μL测试液滴置于水平样品表面，待数值稳定后记录数据，绝对误差为±2.00°。SA值测试：将30 μL纯化水或5 μL正十六烷置于水平样品表面，随后缓慢旋转样品台，直至测试液滴开始滑动，读取此时样品台倾斜的角度，即SA值，水SA值的绝对误差为±0.50°，正十六烷SA值的绝对误差为±1.00°。A和R测试：采用静滴法，液滴注入（A）或抽出（R）的速度为0.02 mL/min，绝对误差为±2.00°。CAH值通过计算A和R的差值得到。每个样品至少平行测定3个不同区域，最终测定结果选用各次测定值的平均值。

2 结果及分析

2.1 动态双疏表面的表征

将Sylgard 184双组分以质量比A∶B=1∶10均匀混合后，A组分聚甲基氢硅氧烷中的硅氢键可与B组分乙烯基聚二甲基硅氧烷中的乙烯基发生交联反应，从而完全固化。若提高A组分的比例至A∶B= 1∶2，则制得的pre-CBDOS中将有硅氢键剩余。体系中剩余的硅氢键可在铂金催化剂的作用下与MVT-PDMS中的乙烯基进行氢化硅烷化反应，从而将液状PDMS链共价键合到pre-CBDOS表面，制得基于液状PDMS的共价键合型动态双疏表面CBDOS，如图1所示。

图1 CBDOS制备

通过ATR-FTIR表征不锈钢基底、S184、pre- CBDOS和CBDOS中特定基团的变化，并监测氢化硅烷化反应过程，如图2所示。结果表明，不锈钢基底曲线中未见明显的有机物特征吸收峰，而S184、pre-CBDOS和CBDOS 3条曲线中都包含PDMS的典型特征峰。其中，Si—O—Si的伸缩振动峰为位于1018、1085 cm–1的双峰，SiMe2中的—CH3对称和非对称变形振动峰分别位于1259、1409 cm–1处，而—CH3的非对称和对称伸缩特征峰则在2906、2962 cm–1处。与S184曲线相比，由于A组分质量比的增大，pre-CBDOS曲线在2160 cm–1处出现了明显的Si—H峰，表明体系中存在可与MVT-PDMS发生反应的Si—H。随着氢化硅烷化反应的进行，CBDOS曲线上并未检测出Si—H峰。这表明体系中的Si—H已完全被消耗，通过其与MVT-PDMS中的乙烯基之间的共价结合，已将PDMS链成功键合到pre-CBDOS表面，从而形成了CBDOS动态双疏表面。

图2 不锈钢基底、S184、pre-CBDOS和CBDOS的ATR-FTIR谱图

采用XPS测试共价键合液状MVT-PDMS前后pre-CBDOS和CBDOS表面的化学组成，数据见表1。通过理论计算，MVT-PDMS中C、Si和O的原子分数分别为50.21%、24.84%和24.95%。由此可见，CBDOS中C、Si和O的原子组成与MVT-PDMS的理论值基本契合，而pre-CBDOS中C、Si和O的原子组成与MVT-PDMS的理论值存在明显差异。因此，XPS测试结果进一步证实了液状MVT-PDMS链已被成功键合到pre-CBDOS表面。低表面能的液状MVT-PDMS链具有高度的移动性和柔韧性，有利于减小液滴与CBDOS表面之间的摩擦因数[50]。同时，PDMS链与表面的共价键合将有效增强表面的稳定性。

利用AFM和FE-SEM分析表征CBDOS的表面形貌，如图3所示。结果表明，CBDOS表面相当均匀平滑，没有明显的聚集或缺陷。同时，AFM数据显示，基底不锈钢片的均方根粗糙度q为5.245 nm，而在其表面构建CBDOS后，q降至0.964 nm。均匀平滑的表面形貌可以减小液滴在表面移动时所需克服的阻力，从而获得较小的SA值和CAH值，有助于CBDOS表面实现卓越的动态抗润湿性能及自清洁功能。

表1 pre-CBDOS和CBDOS的表面原子组成

Tab.1 The surface atomic composition of pre-CBDOS and CBDOS　 at.%

图3 CBDOS表面的AFM和FE-SEM形貌

2.2 动态双疏表面的抗润湿性能

以极性的纯化水和非极性的正十六烷为测试液滴，测定、分析并比较了不锈钢基底和CBDOS表面的抗润湿性能，如图4所示。结果表明，CBDOS表面具有静态疏水亲油、动态双疏的性能。预处理过程在一定程度上改变了不锈钢片的表面形貌，使其水CA值略有变化。而CBDOS表面的水CA值高于不锈钢表面，表明其静态疏水性能优于基底不锈钢片。由于水的表面能较高，正十六烷的表面能较低，因此不论是不锈钢片，还是CBDOS表面，都具有较小的正十六烷CA值。但CBDOS表面的正十六烷CA值仍略高于不锈钢表面，证明其静态双疏性能均强于不锈钢片。进一步考察表面的动态抗润湿性能发现，不论是极性的水，还是非极性的正十六烷，在CBDOS表面都显示出很小的SA值和CAH值。其中，水SA值仅为2.20°，CAH值仅为1.75°，相比不锈钢表面分别降低了95.25%和96.16%；正十六烷SA值为7.33°、CAH值为7.34°，相比不锈钢表面分别降低了14.17%和13.14%。因此，通过在不锈钢表面构建CBDOS，可有效提高材料表面的抗润湿性能。CBDOS表面的水SA值和CAH值均小于3°，正十六烷SA值和CAH值均小于8°，表明表面具有卓越的动态双疏性能，与相关文献报道[27,50,51]的结论一致。

图4 不锈钢基底和CBDOS表面的抗润湿性能

将CBDOS表面于常温常压下静置75 d后，再次测试其抗润湿性能，数据见表2。分析比较发现，液滴在CBDOS表面呈现的CA值、SA值和CAH值变化都很小，极性的水和非极性的正十六烷SA值、CAH值依然都小于8°，表明CBDOS表面具有良好的储存稳定性和稳定的动态双疏性能。

表2 CBDOS表面的抗润湿性能（静置75 d后）

Tab.2 The anti-wettability of CBDOS (deposited for 75 days)

液滴之所以能够容易地从CBDOS表面滑落，可能存在以下3个主要原因[23,27,49,50,52]：第一，CBDOS表面相当均匀平滑，具有纳米尺度的表面粗糙度，这将十分有利于减小液滴的SA值和CAH值；第二，常温下，聚二甲基硅氧烷PDMS为液状聚合物，其主链中的—Si—O—Si—重复单元具有非常强的柔性，共价键合到pre-CBDOS表面后，依然具有高度的移动性和柔韧性，使CBDOS表面好似锚定了一层润滑液，形成了稳定的液状聚合物表层；第三，氢化硅烷化反应发生后，单乙烯基封端的MVT-PDMS链仅有一端被共价键合在pre-CBDOS表面，这将进一步有利于表层液状PDMS保持非常高的移动性和柔韧性。因此，当液滴在均匀平滑的CBDOS表面移动时，具有高度移动性和柔韧性的液状PDMS链可以有效地降低液滴前进或者后退所需的能垒，得到非常小的SA值和CAH值，实现表面的动态双疏性能及自清洁功能。

2.3 动态双疏表面的自清洁功能

不论是极性的还是非极性的液滴，在CBDOS表面都显示出很小的SA值和CAH值，这将有助于液滴顺利地从CBDOS表面滑落，实现自清洁功能。研究选用了生活中常见的8种液体模拟污染物，以便全面地考察CBDOS表面的动态抗润湿性能和自清洁功能，包括纯化水、可乐、茶、食用油、咖啡、醋、酱油和黄酒等。观察50 μL各种污染物液滴在基底不锈钢片和CBDOS表面的形态，如图5所示。结果表明，所有的污染物液滴在CBDOS表面都比在不锈钢片表面更为集中，也就是说液滴在CBDOS表面所具有的CA值都比在不锈钢表面的大，表明CBDOS的静态疏液性能优于基底不锈钢片。

将50 μL不同污染物液滴分别置于不锈钢片和CBDOS表面，随后倾斜表面至10°，观察并比较液滴在不同表面的滑动情况，依次记录于图6中。由图6a可以看出，60 s后，污染物液滴全都仍旧粘附在不锈钢片表面，大部分液滴形状变得更加分散，而位置几乎没有变化。图6b则显示，位于CBDOS表面的污染物液滴全都顺利滑落，并且液滴滑过后，表面保持干燥、洁净，没有明显痕迹，表明液滴在表面没有发生拖尾或粘附。由此可见，CBDOS表面具有全面的动态抗润湿性能，这将使其在实际应用中，对极性或非极性、相溶或不相溶、水溶性或油溶性的污染物都展现出显著的动态双疏和自清洁功能。

进一步模拟户外条件考察CBDOS表面的自清洁功能。图7a以连续的水流模拟雨水冲刷倾斜10°放置的CBDOS表面，结果表明，连续的水流也不会润湿CBDOS表面，而是沿表面成股流下。“降雨”停止后，表面未见明显的液滴粘附或形变。图7b将亚甲基蓝粉末撒落于倾斜10°放置的CBDOS模拟户外灰尘粘附后的表面，再滴落1滴100 μL纯化水。随着水滴滑落，CBDOS表面的“灰尘”可被水滴完全带走，从而使表面重新恢复洁净。研究也对CBDOS的户外应用进行了初步探索。将CBDOS分别于户外放置5、10、15 d后，以纯化水洗净表面，并于50 ℃烘干，测试其表面水CA值分别为108.61°、108.83°、108.40°，与户外测试前的CBDOS表面性能基本一致。CBDOS表面优异的自清洁功能可助其在雨水作用下去除表面粘附的污染物，恢复表面性能，使其有望应用于建筑外墙、海洋防污等户外场景。

图5 污染物液滴在不锈钢和CBDOS表面的形态

图6 不锈钢和CBDOS表面的自清洁功能

图7 CBDOS表面在模拟户外条件下的自清洁功能

3 结论

1）通过非化学计量比的pre-CBDOS表面剩余的硅氢键和单乙烯基封端MVT-PDMS之间的氢化硅烷化反应，成功制得具有卓越动态双疏性能和自清洁功能的共价键合型CBDOS表面。本研究方法简便，条件温和，对环境无污染，并且适用于惰性基底。

2）CBDOS表面显示出极低的水和正十六烷SA值、CAH值。其中，极性的水SA值为2.20°、CAH值为1.75°，非极性的正十六烷SA值为7.33°、CAH值为7.34°，都小于8°。均匀平滑的表面形貌与单端共价键合的液状MVT-PDMS所具有的高度移动性和柔韧性是CBDOS获得低SA值、CAH值及动态双疏性能的关键要素。同时，由于液状PDMS链是共价键合在CBDOS表面的，可有效提高表面的稳定性。

3）CBDOS表面具有全面的动态抗润湿性能，对极性或非极性、相溶或不相溶、水溶性或油溶性的污染物都展示出良好的自清洁功能，并可在液体冲刷下轻松去除表面粘附的粉尘，这将使其有望应用于医药卫生、食品加工、建筑外墙、海洋防污等诸多领域。

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Fabrication and Self-cleaning Function of Covalently-bonded Dynamically-omniphobic Surface Based on Liquid-like PDMS

(School of Pharmacy, Quanzhou Medical College, Fujian Quanzhou 362011, China)

To fabricate a stable surface with dynamic omniphobicity and self-cleaning function on inert substrates, in this paper, a facile approach was developed. The covalently-bonded dynamically-omniphobic surface (CBDOS) was prepared on inert stainless steel substrate by hydrosilylation, which was reacted between the Si-H bond in non-stoichiometry silicone rubber and monovinyl terminated polydimethylsiloxane. CBDOS was transparent, smooth, flouride-free and stable. Then, ATR-FTIR and XPS were used to characterize the chemical composition, which confirmed that liquid-like PDMS had been successfully covalently boned to CBDOS surface. AFM and FE-SEM were used to analyze the surface topography, and the results showed that CBDOS surface considerably smooth with nanoscale roughness. The AFM-derived root mean square roughness (q) of CBDOS surface was only 0.964 nm. Drop shape analyzer was used to study the anti-wettability and measure values of contact angle (CA), sliding angle (SA) and contact angle hysteresis (CAH). The water SA and CAH values were 2.20° and 1.75°, and n-hexadecane SA and CAH values were 7.33° and 7.34°, respectively. The data indicated that CBDOS revealed excellent dynamic omniphobicity and well storage stability. Therefore, CBDOS had outstanding self-cleaning function toward many kinds of common contaminants, whether they were polar or non-polar, soluble or insoluble, water-soluble or oil-soluble. It was believed that there were two key factors for CBDOS to realize excellent dynamic omniphobicity and self-cleaning function, one was the extremely homogeneous and smooth surface morphology, the other was the high mobility and flexibility of liquid-like PDMS which was only one end covalently grafted to CBDOS surface. This approach had lots of advantages such as simple operation, mild conditions and non-pollution, in addition, it could be applied to all types of substrates. Furthermore, due to the strategy of covalently bonding, the stability of dynamically omniphobic surfaces based on liquid-like PDMS had been improved distinctly.

polydimethylsiloxane; liquid-like polymer; hydrosilylation; covalent bonding; dynamic omniphobicity; self- cleaning

TB34

A

1001-3660(2022)04-0356-09

10.16490/j.cnki.issn.1001-3660.2022.04.038

2021-03-29；

2022-01-04

2021-03-29；

2022-01-04

泉州市医疗卫生领域指导性科技计划项目（2021N126S）

The Quanzhou Guiding Science and Technology Project in the Medical and Health Field (2021N126S)

黄颖芬（1982—），女，博士，讲师，主要研究方向为功能高分子。

HUANG Ying-fen (1982—), Female, Doctor, Lecturer, Research focus: functional polymer.

黄颖芬. 基于液状PDMS的共价键合型动态双疏表面及其自清洁功能[J]. 表面技术, 2022, 51(4): 356-364.

HUANG Ying-fen. Fabrication and Self-cleaning Function of Covalently-bonded Dynamically-omniphobic Surface Based on Liquid-like PDMS [J]. Surface Technology, 2022, 51(4): 356-364.

责任编辑：刘世忠