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| 仿生超浸润材料用于水下气泡的定向输运机理及应用研究 | |
| 其他题名 | Study on the mechanism and application of the directional transportation of gas bubbles based on superwettability |
| 于存明 | |
| 出版年 | 2017 |
| 学位类型 | 博士 |
| 导师 | 赵学勇 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 在亿万年的自然选择中，自然界的生物进化出臻于完美的结构与系统，以适应复杂的自然环境。例如荷叶表面的超疏水结构使其出淤泥而不染、沙漠甲虫表面的亲/疏水复合结构可以有效收集沙漠清晨雾气中的水滴，蜘蛛丝及仙人掌的锥形结构有利于其收集空气中的水滴作为补充水源、猪笼草润滑口缘内壁可以防止其捕获的猎物逃走……受此启发，基于特殊浸润性的仿生材料蓬勃发展。受荷叶启发，人们制备了超疏水自清洁表面；受沙漠甲虫启发，人们制备了亲/疏水协同的雾水收集系统；受蜘蛛丝和仙人掌启发，人们制备了锥形雾水收集系统及微油滴收集系统；受猪笼草润滑内壁启发，人们制备了超润滑Slippery表面，可以有效防止血液粘附……然而目前浸润性的研究，主要局限在空气中的固-液-气三相体系，水下的固-气-液三相体系很少被涉及。水下气泡在固体表面的行为不仅与生物的生活息息相关，而且在人类的日常生活、工业生产、军事等领域存在重要的应用。例如水蜘蛛可以依靠具有超疏水性能的腹部束缚气泡在水下存活多达数十天之久，气泡在矿物表面的粘附在矿物浮选领域存在广泛应用，潜艇表面吸附的气泡可以有效降低潜艇在水下运动时的阻力等等。然而，气泡在水下的行为受浮力的影响巨大，现存的方法很难实现气泡的定向、可控操控。因此，研究气泡在固体表面的行为，实现气泡的定向、可控输运，具有填补理论空白、进行应用探索的双重意义。基于此，本论文由以下三个部分组成：1. 超疏水仿生仙人掌锥形结构用于水下气泡的自发及定向输运机理研究。自然界中的仙人掌锥形结构，可以有效收集雾气中的微小液滴，并且定向地输运到仙人掌刺的根部。受此启发，我们通过电化学梯度腐蚀及表面浸润性修饰的方法制备了超疏水铜锥，其可以有效捕获水中气泡，并且将捕获的气泡快速、定向地输运到锥的根部。其中，气泡定向运动的驱动力源于锥形结构导致的气泡前、后两端所受的拉普拉斯压强不同。在文中，我们还研究了表面浸润性、锥角、气泡体积、锥的倾斜角度对于气泡输运的影响。研究发现，超亲水及亲水的铜锥均不能捕获气泡，疏水铜锥可以捕获水中气泡、但不能将其进行有效输运，超疏水铜锥既可以有效捕获气泡、同样可以对其进行有效输运。锥角及气泡体积对气泡的输运速率存在重要的影响。锥角越大，气泡体积越小，气泡在锥上的运动速率越大。通过对锥倾斜角的研究发现超疏水铜锥可以实现各个方向上（包括反浮力方向）的气泡输运。2. 具有仿生仙人掌锥形结构的亲气电极用于氢气的持续生产、定向输运及有效收集研究。气泡粘附是析氢反应中亟待解决的问题。目前的方法大都是在电极表面构筑微、纳结构，增大电极的比表面积，降低电极对气泡的粘附力，缩短气泡在电极表面的粘附时间。然而该策略会提高溶液中溶解氢的浓度，其对产氢反应的持续、安全进行会造成不利的影响。受前面工作的启发，我们制备了具有锥形结构的亲气电极，将其应用到析氢反应中。与雾滴在仙人掌刺表面的运输过程相似，锥形亲气电极表面生成的微小气泡在拉普拉斯压强差的作用下可以向锥型电极的根部快速运动，在运动的过程中，气泡会融合成大气泡，当气泡接触到超亲气海绵，气泡会被快速吸收。3. 超疏水螺旋结构用于水下气泡的可控及定向输运研究。受制备方法的限制，超疏水铜锥只能理论上实现气泡的长距离输运，实际操作困难重重。为了解决气泡的可控及长距离输运问题，我们在本章中制备了超疏水螺旋，其在水下不但可以实现长距离的气泡传输，还可以通过调控倾斜角度实现气泡的反浮力输运。螺旋转速(r)及间距(d)对气泡的运输速率(v)存在影响，三者之间的关系为：v = r × d。此外，通过对螺旋方向及其旋转方向的调控，可以实现对气泡输运方向的控制。实验中我们将两个相反方向的超疏水螺旋有机组合，可以实现气泡的分离及合并，并将其做为水下气泡微反应器，实现氢气、氧气的水下反应。此外，超疏水螺旋还可以捕获水下气泡、实现多个气泡的持续输运。 |
| 英文摘要 | After billions of years of evolution, natural creatures have evolved intriguing survival skills to adapt to the complex environment. For example, the superhydrophobic structure on lotus leaf protects the leaf from contaminating by mud; the hydrophilic/hydrophobic patterns on the back of desert bettle endows the bettle with outstanding ability of fog collection; the conical morphologies of spider silk and cactus spine contribute them to efficiently collect tiny water droplets from environment as additional water supply; the inner slippery wall of Nepenthes pitcher benefits the plant with ability of preveting the captured species from escaping. Inspired by these organisms, people have developed lots of biomimic materials based on superwettability. For example, learning from lotus leaf, people have fabricated superhydrophobic and self-cleaning materials. Taking inspirations from desert bettle, people have fabricated novel fog collecting system with hydrophobic/hydrophilic patterns. Inspired by the spider silk and cactus spine, people have prepared intergrated cone arrays, which could efficiently collecting fog droplets from air and tiny oil droplets from water. Larning from the Nepenthes pitcher, People have devolped Slippery surface, which could efficiently prevent the adhesion of blood, demonstrating potential applications in medical field. However, most of the researches are focused on the behaviors of liquid droplet on solid surface in air environment and the behaviors of gas bubbles on solid surface underwater are less cared about.Gas bubbles in aqueous media are ubiquitous in natural world, industrial production and daily life. For example, the water spider could survive in water as long as dozens of days under the assistant of its superhydrophobic abdomen, which could carry air bubble as “physical lung” to exchange oxygen underwater; the behaviors of gas bubbles adhered on solid surface is wildly applied in the recovery of valuable minerals from ores; the attachment of gas bubbles on the surface of submarine is beneficial to reduce the drag force of water to the submarine. However, the behaviors of gas bubbles in water are mainly governed by the buoyancy force and gas bubbles are apt to move upward. Therefore, understanding the behaviors of gas bubbles and realizing the reliable bubble manipulation in aqueous media are crucial to both scientific research and industrial applications. Based on this background, we have carefully investigated the behaviors of gas bubbles in aqueous environment and realized their reliable manipulation, which demonstrated in the following three parts:1. Spontaneous and Directional Transportation of Gas Bubbles on Superhydrophobic Cones. In nature, the conical morphology of cactus spine facilitates the spine with outstanding ability of efficiently capturing tiny fog droplets and directionally transporting them towards the base side of spine. Inspired by this, through gradient electrochemical corrosion and surface wettability modification, we have fabricated the superhydrophobic copper cones, which were capable of efficiently capturing bubbles from water and transporting them to the base side of cone. The Laplace pressure gradient arising from the conical morphology of superhydrophobic cone is believed to be the driving force for the directional transportation of captured bubbles. In this part, the factors of surface wettability, apex angle, volume of bubbles, tilt angles, were also investigated. All of them are vital importance in determining the transportation velocity of gas bubbles. Both of the superhydrophilic and hydrophilic copper cones failed to capture or transport gas bubbles. The hydrophobic copper cone could capture gas bubbles from water but failed in transporting bubbles. The superhydrophobic cones can trap gas bubbles efficiently and transport the captured bubbles to their base with high velocity. The high apex angle of cone and the miniature size of bubble were beneficial to the bubble transportation. The superhydrophobic copper cones are capable of transporting gas bubbles spontaneously and directionally underwater, even when they are vertically fixed with tips pointing up.2. Aerophilic electrode with cone shape for continuous generation and efficient collection of H2 bubbles. The bubbles adhesion on electrode is a serious issue facing hydrogen evolution reaction, which greatly impedes the sufficient production of hydrogen. To date, the strategy of constructing micro/nano structures on the electrode, which could shorten the adhesion time, is popular in improving the efficiency of hydrogen evolution reaction. However, the gas bubbles directly releasing into electrolyte will increase the concentration of hydrogen and oxygen in electrolyte and lead to security issues in practical operation. Inspired by the previous work, we have fabricated the cone-shape aerophilic electrode applied in hydrogen evolution reaction. Similar with the process of fog collection on the cactus spine, the aerophilic copper electrode with cone shape could be capable of directionally transporting the as-formed hydrogen bubbles along its surface to the base. By integrating the aerophilic conical electrode with the superaerophilic sponge, the transported hydrogen bubbles can be efficiently absorbed.3. Superhydrophobic helix: Controllable and directional bubble transport in aqueous environment. Although achieving the long distance transportation of bubbles in theory, the practical transportation of bubbles was greatly limited by the length of superhydrophobic cone. To accomplish the controllable and long distance transportation of bubbles, we have prepared the superhydrophobic helix, which could realize the anti-buoyance and long distance transportation. The bubble transportation velocity (v) is determined by the rotation speed (r) and spacing distance of helix (d). The relationship of them is v = r × d. And the direction of gas transportation can be adjusted by changing the spiral direction of helix. Based on this, we fabricated the asymmetric superhydrophobic helix, which was composed of two helixes with contrary directions. The integrated helix is able to realize the separation and coalesce of gas bubbles, which can be regarded as underwater micro-reaction of gas bubbles. Furthermore, the superhydrophobic helix could be capable of capturing bubbles underwater and realizing the continuous transportation of gas bubbles. |
| 中文关键词 | 仿生 ; 特殊浸润性 ; 拉普拉斯压强差 ; 气泡 ; 定向及可控输运 |
| 英文关键词 | biomimic materials superwettability Laplace pressure gredient bubbles directional and contralloable transportation |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 物理化学 |
| 来源机构 | 中国科学院化学研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287833 |
| 推荐引用方式 GB/T 7714 | 于存明. 仿生超浸润材料用于水下气泡的定向输运机理及应用研究[D]. 中国科学院大学,2017. |
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