Icephobic Strategies and Materials with Superwettability: Design Principles and Mechanism

Abstract

Ice formation and accretion on surfaces is a serious economic issue in energy supply and transportation. Recent strategies for developing icephobic surfaces are intimately associated with superwettability. Commonly, the superwettability of icephobic materials depends on their surface roughness and chemical composition. This article critically categorizes the possible strategies to mitigate icing problems from daily life. The wettability and classical nucleation theories are used to characterize the icephobic surfaces. Thermodynamically, the advantages/disadvantages of superhydrophobic surfaces are discussed to explain icephobic behavior. The importance of elasticity, slippery liquid-infused porous surfaces (SLIPSs), amphiphilicity, antifreezing protein, organogels, and stimuli-responsive materials has been highlighted to induce icephobic performance. In addition, the design principles and mechanism to fabricate icephobic surfaces with superwettability are explored and summarized.

Bioinspired Superhydrophobic Progress and Recent Advances of Its Functional Application

“…目前的超疏水防覆冰领域主要体现在三个方面: 减少液滴与界面长时间接触(小液滴在过冷条件下 的反弹)、降低凝固点及延迟结冰时间(微小冷凝液 滴的自跳动现象)和构建疏冰低结冰粘附力表面(滑 液面防冰)。当固-液界面出现结冰现象时, 表面结 冰过程可用开尔文方程和克拉伯龙方程分析小液滴 的分类形核理论和抑制形核能理论 [84] 来分析该表 面的防覆冰能力(图 3)。 超疏水表面普遍存在小液滴弹跳现象 [87][88][89] , 其 原因为遭到液滴撞击时的小液滴动能不易转变为超 疏水表面内能 [90][91] , 超疏水涂层的表面张力较小 (图 4)。因此, 当低温环境下的超疏水表面出现弹跳 现象时, 弹跳的液滴于结冰形核前离开超疏水表面, 从而减缓界面的过冷传输过程, 达到防覆冰的目 的。Quéré 课题组 [92] 研究表明, 液滴以 20~230 cm/s 的速度撞击超疏水表面时, 液滴和界面的接触时间 仅与液滴半径和界面张力有关, 与撞击速度无关。 冷凝在微纳结构内部的小液滴受限于粗糙结构 而导致其形状改变, 小液滴汇集结合后的液滴自由 能过剩, 即表面自由能大于液滴平衡态自由能, 最 终液滴在低表能的超疏水表面弹起或滚动离开 [93] , 宏观表现为小液滴连续的自跳动现象(图 5)。 通过控 制微纳结构的尺寸变化及其不同的结构粗糙度, 可 提高超疏水表面的自跳动防冰效果 [94][95][96] 。超疏水涂 层的表面能较小且静态接触角较大, 导致液滴与超 疏水表面的接触面积较小。根据小液滴的分类形核 理论和抑制形核能 [84] , 控制超疏水表面的粗糙度小 于且无限接近于临界晶核的最小半径值 [97] , 此时, 超疏水表面具有结冰延迟效果 [98][99] 。 覆冰与物体表面存在范德华力、氢键作用和静 电引力(表 3)。 界面接触时范德华力普遍存在且与接 触面面积呈现线性关系, 具有亲水基团表面的氢键 作用较强, 静电引力是三种作用力中最重要的影响 结冰粘附力因素, 材料的介电常数越低, 覆冰的静 电引力作用越小 [100] 。研究表明, 低表面能的超疏水 表面可降低覆冰的粘附力 [101][102][103][104][105][106][107] , 但由于超疏水表 面形貌和微纳结构的差异, 具体的防结冰及降低覆 冰粘附力的机理研究还有待完善。 图 2 高透明超疏水涂层 [80][81] Fig. 2 (a) Transparent and durable superhydrophobic glass [80] and (b) highly transparent and superhydrophobic nanopaper [81] 无 机 材 料 学 报 第 34 卷 图 3 防-疏冰机理和小液滴形核结冰过程 [85][86] Fig. 3 (a) Mechanisms of anti-icing and ice-phobic surface [85] ; (b) Schematic diagram showing the regions within a water droplet where homogeneous and heterogeneous ice nucleation occurs; (c) Gibbs free energy barrier during freezing process against the ice embryo radius (Below critical size the ice embryo is metastable and above critical size the ice embryo is stable to initiate the freezing process) [86] 图 4 超疏水表面的小液滴弹跳现象 [87]…”

“…2 (a) Transparent and durable superhydrophobic glass [80] and (b) highly transparent and superhydrophobic nanopaper [81] 无 机 材 料 学 报 第 34 卷 图 3 防-疏冰机理和小液滴形核结冰过程 [85][86] Fig. 3 (a) Mechanisms of anti-icing and ice-phobic surface [85] ; (b) Schematic diagram showing the regions within a water droplet where homogeneous and heterogeneous ice nucleation occurs; (c) Gibbs free energy barrier during freezing process against the ice embryo radius (Below critical size the ice embryo is metastable and above critical size the ice embryo is stable to initiate the freezing process) [86] 图 4 超疏水表面的小液滴弹跳现象 [87][88][89] Fig. 4 Droplet bouncing dynamics on superhydrophobic surface [87][88][89] 受仿生猪笼草研究的启发 [34] , 研究者构建多孔 结构水润滑层 [108][109] 以实现表面疏冰、抗冰的效果 (图 6)。其构建过程中应满足三个要求: 水润滑层液 体与外来浸润液体不相容; 水润滑层与基体的吸附 力优于外来浸润液体在其滑液面的化学亲和力; 保 证水润滑层液体可以持久地贮存在多孔结构中, 且 图 5 (a~c)冷凝液滴的自跳动行为 [94][95][96] 和(d, e)延迟结冰现象 [98][99] Fig.…”

Hydrophobic and Anti-Icing Behavior of UV-Laser-Treated Polyester Resin-Based Gelcoats

“…This idea was copied from nature, as there are some naturally occurring structured superhydrophobic materials, with the lotus leaf as a key example [16]. There are multiple research studies on the topic of designing icephobic structures and the relation between hydrophobicity and anti-icing properties [17][18][19]. In the article [20], different artificially created patterns were tested, including posts, bricks, blades and honeycombs and the conclusion was drawn that the design of nanostructured materials should in fact lead to reducing or eliminating ice accumulation.…”

“…In scientific literature, the interest in this type of material construction has been observed over a relatively short period, since the first decade of the 21st century. From the point of view of the complexity of the structure (at the micro-or nanometric level), icephobic coatings are characterized by a much higher level of complications and complexity compared to hydrophobic surfaces [17]. This observation is important in the context of the division of modifiers used in icephobization technologies.…”

Graphene tailored by Fe3O4 nanoparticles: low-adhesive and durable superhydrophobic coatings

“…Research efforts on exploiting superhydrophobic surfaces were focused on constructing hierarchically micro/nano structures, as well as modifying surfaces by inorganic/organic oxides or uorides with low surface energy. [14][15][16][17][18][19] The physical strategy is able to maintain the physicochemical properties of the graphene surface, with few side effects on the surrounding environment. The design of micro/nanostructures 20,21 is considered to be a good approach to enhance the surface hydrophobicity.…”