聚硅氧烷超疏水表面制备及其性能研究

【作者】 杨昊炜；

【导师】 肖斐；

【作者基本信息】 复旦大学 ， 材料物理与化学， 2011， 博士

【摘要】 超疏水表面由于对水展现出非常高的接触角和很低的接触角滞后(滚动角),在自清洁、防冰、防腐蚀、减阻、油水分离等领域具有广阔的应用前景而备受关注。目前已经制备了很多性能优异的超疏水表面,不过其实际应用仍有不少亟待解决的问题：制备方法上,一些已有的手段实用性较差,只适用于实验室研究而无法方便地得到大面积的超疏水表面；稳定性上,超疏水表面的稳定性受组成材料的影响,普通碳链聚合物在受热、户外应用时容易失去疏水性。因此选择合适的材料,开发操作方便、重复性好、能大面积施工的超疏水表面制备方法,得到稳定性优良的超疏水表面十分有必要。聚硅氧烷主链为Si-O-Si,不易被紫外光和臭氧分解,比其他高分子材料有更好的热稳定性、耐辐照性和耐候能力,而且其链上含有疏水基团,制备超疏水表面时无需疏水化处理。本文选取聚硅氧烷为主要材料,研究材料、制备方法对表面结构、疏水性能和稳定性的影响,开发简单、实用化的制备方法,获得性能稳定的超疏水表面,为超疏水表面的应用提供实践依据。本文首先进行了聚丙基一甲基倍半硅氧烷(PPMSSQ)超疏水薄膜的制备方法研究。利用溶胶一凝胶过程中失稳分解引起的相分离,在两片载玻片间的密闭空间制备PPMSSQ凝胶,分离后得到多孔薄膜。薄膜的表面粗糙程度受相分离的影响,随添加氨水量增加而增大。氨水较多时,薄膜表面与水的接触从Wenzel态转变为Cassie态,可获得超疏水PPMSSQ薄膜。但该方法实用性较差,为使制备PPMSSQ超疏水薄膜的方法更加实用化,研究了溶胶镀膜时前体中甲基三乙氧基硅烷(MTEOS)与丙基三乙氧基硅烷(PTEOS)比例、老化、外加水等条件对PPMSSQ溶胶形态、薄膜形貌及疏水性的影响。结果表明,PPMSSQ溶胶未经老化时,毛细作用力引起薄膜表面孔洞塌缩,得不到超疏水性；PPMSSQ溶胶老化后,为延缓凝胶过量加入的溶剂降低了溶胶骨架与溶剂间的相分离程度,镀膜表面粗糙程度降低,也得不到超疏水性；在老化溶胶中加入水能够有效地诱导溶胶骨架与溶剂发生相分离,相互簇集,提高镀膜表面的粗糙度；提高PTEOS的比例可以增加溶胶骨架与溶剂间的不相容性,粗糙镀膜表面,而且丙基的空间位阻可以降低反应速度,避免过早凝胶,但是PTEOS浓度过高时,又会引起溶胶骨架与溶剂间极性相差过大而过早宏观分相；当PTEOS:MTEOS体积比为3：7时,PPMSSQ老化溶胶能在加入水后有效簇集,骨架簇集程度随加入水的增多而增大；加入适量水时,提拉得到的薄膜有合适的表面微米纳米粗糙结构,获得接触角大于155°、滚动角小于10°的超疏水薄膜。因而得到了实用化的制备PPMSSQ超疏水薄膜的方法一水诱导相分离法。其次对水诱导相分离PPMSSQ超疏水薄膜的热稳定性及失效机理进行了研究。PPMSSQ超疏水薄膜在200℃以下处理能够保持超疏水性,200℃以上随热处理温度的升高逐步失去超疏水性。SEM、FTIR、TG-DTA分析表明超疏水性消失来自于凝胶骨架纳米粒子间的融合和疏水基团分解的共同作用。本文又进行了热稳定超疏水涂层的制备与研究。合成了具有优异热稳定性的聚苯基倍半硅氧烷(PPSQ), XRD、29Si CP-MAS NMR、FTIR表征证实其分子链均具有典型的梯形结构,结合苯基的耐热性,PPSQ相比于其他聚硅氧烷(DowCorning840硅树脂与RTV硅橡胶)有更好的耐热性能,500℃以下空气气氛中稳定。空气喷涂含纳米SiO2的PPSQ分散液,研究SiO2添加量对SiO2/PPSQ涂层表面形貌及疏水性的影响,获得SiO2/PPSQ超疏水涂层,其表面微米结构源于喷涂法对雾化粒子外形的保持(强制干燥效应),纳米结构来自较多纳米Si02的添加。不添加纳米SiO2,制备了良溶剂-不良溶剂法PPSQ超疏水涂层,其微米结构同样源自喷涂法强制干燥效应,纳米结构来自PPSQ的微相分离。研究了这两种超疏水涂层的热稳定性,良溶剂-不良溶剂法PPSQ超疏水涂层200℃以上失去超疏水性,而SiO2/PPSQ涂层的超疏水性在500℃空气气氛处理后依旧保持。SEM观测及FTIR分析表明前者的失效由PPSQ的热软化和融合引起涂层表面粗糙结构消失所致,后者优异的热稳定性得益于SiO2刚性的粗糙结构,以及PPSQ分子优异的耐热性能。表明在超疏水结构中掺入刚性纳米粒子有助于提高其热稳定性,另外热稳定超疏水SiO2/PPSQ涂层有望在需要耐热的场合应用。目前超疏水表面的功能性主要来源于表面疏水性与粗糙结构,本文最后引入功能性纳米粒子,探索研究赋予超疏水表面功能性的其他途径。研究了导电碳黑(CB)EC-300在室温固化聚二甲基硅氧烷(PDMS)橡胶体系中的分散。在此基础上,优选醋酸丁酯为溶剂,BYK 9077为润湿分散助剂,砂磨使EC-300良好分散,并添加具有导磁性的纳米Ni粒子,空气喷涂制备Ni/CB/PDMS涂层。一定CB添加量下,研究Ni添加量对涂层表面形貌,疏水性和电磁屏蔽能力的影响。结果显示,由于添加了纳米颗粒,涂层表面具有纳米结构,而增加Ni含量能够减小雾化涂料颗粒飞抵基底后的流动性和相互融合的可能,增加涂层表面微米突起的高度,使涂层表面的三相接触线从连续变为不连续,从而实现涂层润湿性从高粘附力向低粘附力态转变。同时,添加更多Ni粒子能增加导磁性,提高Ni/CB/PDMS涂层高频下的电磁屏蔽能力。该研究表明在纳米粒子/聚合物涂层体系中,添加纳米粒子,不但可以作为填料改变涂层表面微米纳米粗糙结构,控制疏水性质,还可以利用纳米粒子本身的特性,赋予超疏水表面功能性,拓宽超疏水表面的应用领域。更多还原

【Abstract】 Superhydrophobic surfaces call full attention because they possess ultra large water contact angle and quite small contact angle hysteresis(sliding angle),and show potential application in areas such as self-cleaning, anti-icing, anti-corrosion, drag reduction and water oil separation, and etc. Quite a large number of superhydrophobic surfaces with excellent properties have been obtained at present. However, many efforts are still needed to take the superhydrophobic surfaces into real application:On one hand, many fabrication methods are only suitable for lab research, which are not convenient to produce large area superhydrophobic surfaces. On the other hand, the stabilities of the superhydrophobic surfaces are influenced by the materials made of. For example, carbonic polymers are suffered from the losing of their hydrophobicity outdoors and under high temperature. Therefore, it is very important to choose proper materials, develop reproducible and convenient fabrication methods with large area preparing capability, to get stable superhydrophobic surfaces. Polysiloxanes, profit from their Si-O-Si chains, are good candidates for their good thermal and O3 stability, UV and radiation stability, and weatherability compared with normal polymers. Furthermore, post hydrophobic modification treatment is not necessary when fabricating a polysiloxane superhydrophobic surface, because the existence of hydrophobic groups on polysiloxane. In this dissertation, polysiloxanes are chosen to make stable superhydrophobic surfaces for applications on the basis of disclosing the influences of materials and methods on surface structures, wetting properties and stabilities. Also, simple and effective methods are desirable.To begin with, polypropyl-methylsilsesquioxane (PPMSSQ) superhydrophobic preparing methods are investigated. Films are made by splitting the two slides, between which the sol-gel transition is conducted and a porous structure is made by the spindal decomposition phase separation between the sol skeleton and the solvent. Surface roughness is controlled by the ammonia added and the phase separation thereof. With more ammonia, rougher surface makes the Wenzel to Cassie mode transition, and obtain the superhydrophobicity. However, it is not compatible with conventional coating methods, so the influences of the MTEOS to PTEOS precursor ratio, aging and water adding conditions on the PPMSSQ sol, thin film morphologies, and the wetting properties are investigated in sol dip coating method. It reveals that superhydrophobicity disappears when rough structures at the film surfaces are destroyed by the capillary force introduced by the solvent evaporation employing the fresh sols, or the reduced skeleton-solvent phase separation degree by the extra solvent in aging. Adding water into the aged sols can induce the phase separation between sol skeleton and solvent, lead to aggregation of the skeleton and enlarge the film surface roughness. More PTEOS enhances the phase separation, roughen the surface, and prevent gelling too fast because of its steric hindrance, yet too more PTEOS, which means macro phase separation, makes the sol unstable. When PTEOS: MTEOS=3:7(in volume), the PPMSSQ sol skeletons aggregate effectively, more water, larger aggregation and rougher surfaces. A superhydrophobic surface with contact angle larger than 155°and sliding angle smaller than 10°can be gained under proper water volume condition. Thus we acquired the meaningful PPMSSQ preparing method, that is, the water induced phase separation method.To move on, the thermal stability and failure mechanism of the water induced phase separation superhydrophobic (WIPS-SHS) PPMSSQ film has been studied. The WIPS-SHS PPMSSQ film keeps its superhydrophobicity below 200℃,and gradually loses it with temperature increasing above 200℃, caused by merging of the nano skeletons and loss of hydrophobic groups, as revealed by SEM,FTIR and TG-DTA.The next chapter of the dissertation focuses on the preparing and researching of the thermal stable superhydrophobic surfaces. Polyphenylsilsesquioxanes (PPSQ) with excellent thermal stability have been synthesized. Combined with the stable phenyl group and the ladder structure confirmed by XRD,29Si CP-MAS NMR and FTIR studies, the PPSQ demonstrates outstanding thermal stability up to 500℃in air, compared with other polysiloxanes as DowCorning 840 resin and RTV silicone elastomer. Employing slurry with nano SiO2 particles and PPSQ to prepare SiO2-PPSQ coatings by air spraying, and studying how the SiO2 content will influence the coating surface structures and wetting properties. Then superhydrophobic SiO2-PPSQ coatings are produced. The prepared SiO2-PPSQ coatings possess micro and nano hierarchical structures, and the micro structure is stemmed from the atomized slurry particles (termed as the enforced evaporation effect of spraying) while the nano structure is the consequence of the nanoparticles introducing. A solvent-nonsolvent superhydrophobic PPSQ coating is prepared as well, whose micro structure is the analog of the superhydrophobic SiO2-PPSQ coatings, and nano structure is induced by micro phase separation of PPSQ. The solvent-nonsolvent superhydrophobic PPSQ coating loses its superhydrophobicity above 200℃on account of the elimination of nanostructures by the thermal softening of PPSQ, and superhydrophobicity of the SiO2-PPSQ coating retains up to 500℃, sustained by the rigidity of the filled SiO2 and excellent thermal stability of PPSQ, which is revealed by FTIR, SEM analysis. It indicates that embedding rigid nanoparticles into the thermal soft structures helps to retain the roughness and keep superhydrophobicity stable.Currently, functionalities of superhydrophobic surfaces are mainly based on the low surface tension and rough structures. Exploration of granting superhydrophobic surfaces functions by embedding functional nanoparticles is conducted. Dispersing effects of the Carbon Black (EC-300) into RTV PDMS are examined; finding out that BYK 9077, butyl acetate and sand milling is benefit for good dispersing. The Ni/CB/PDMS coatings are prepared by spray coating, and researches on the influences of Ni content under given CB loading on surface structures, wetting property and EMI shielding property are conducted. It is found that more Ni can prohibit the atomized paint particles from merging together and make the micro perturbation more distinct on surface, thus transit the three contact line from connected to disconnected, and accomplish the transition from a sticky surface to a roll off surface. Meanwhile, more Ni increases the permeability and enhances the EMI shielding ability of the coating at high frequency. It brings to light that nanoparticles can not only serve as filler to control the surface structures and the wetting property, but also impart superhydrophobic surfaces with functionality to enlarge their application area.更多还原