NER: Nano-Textured Surfaces: Super-Hydrophobicity and Liquid Adhesion

NER：纳米纹理表面：超疏水性和液体粘附力

• 批准号: 0103514
• 负责人: Frederick Lange
• 金额: --
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-08-01 至 2002-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0103514&HistoricalAwards=false
• 关键词: NER; Nano; Textured; Surfaces; Super

0103514Lange This proposal was submitted in response to the solicitation "Nanoscale Science and Engineering" (NSF 00-119) Surfaces can be made either super-hydrophobic or super-hydrophilic by producing a textured surface that resembles hills and valleys, provided that the wetting angle of the liquid on a flat surface of the same material is 90 degree . The mechanism that produces the effect is based on the fact that the liquid only wets the tops of the hills and gas (air) is trapped within the valleys. Simple analytical functions have been developed for different periodic, textured surfaces to show that the wetting angle is related to the area fraction of wetted 'hills' and the wetting angle for a flat surface. The lotus leaf is a natural example of a super-hydrophobic surface. In 1997, micron size wax bumps were discovered to produce this effect. Water drops on the lotus leaf are nearly spherical (q ~ 170 degree) and easily roll around collecting dust particles to produce a self-cleansing effect that has made the lotus plant revered for its purity. Synthetic super-hydrophobic surfaces have been produced by coating a surface with a 'rumbled' thin film and with a micromolding method. These surfaces are promising for practical applications that include rain-repellent surfaces, surfaces designed to decrease the resistance to fluid flow, and surfaces designed for selective liquid condensation.Recently, we demonstrated that super-hydrophobic surfaces could be produced by simply dip-coating a substrate into a slurry containing small, dispersed particles. The particles were attracted to the substrate by to their opposite surface charge, relative to the substrate. We demonstrated that the area fraction and particle size can be systematically controlled and that surfaces can be textured with commerically available particles in the range of 5 nm to 300 nm. By reacting the surface with fluoroalkyltrichlorosilane molecules, a flat surface is rendered hydrophobic, and super-hydrophobic, when textured.We observed that the super-hydrophobic effect was related to the area fraction of adsorbed silica particles and that the super-hydrophobic effect disappears when the average spacing between the spherical particles exceeds a critical value. When the particles are very small the water droplet shows absolute adherence to the surface. Both of these latter two effects can be predicted with the Laplace equation, which relates the equilibrium curvature of a meniscus to the pressure exerted by the water drop. Systematic experiments are planned with nano-textured surfaces to study these two new phenomena in relation to specific functions derived with the Laplace equation. This will be accomplished using glass substrates that will be coated with colloidal silica particles that are commercially available in the size range of 5 nm to 300 nm. The prepared nano-textured surfaces will consist of randomly distributed silica sphere on a glass substrate. The silica particles will be fixed to the substrate by sintering. The nano-textured substrates will then be reacted with fluoroalkyltrichlorosilane molecules to ensure optimum hydrophobicity. All experiments will be conducted with deionized water on nano-textured surfaces treated with the same fluoroalkyltrichlorosilane molecules. With these constrains, the surface energy per unit area, g, and the contact angle of a flat surface, q, will be keep constant.Spontaneous Wetting Experiments: Spontaneous wetting will occur when the Laplace pressure exceeds a critical value to produce an instability; spontaneous wetting is expected to be a strong function of both the area fraction and particle size. Experiments will be designed to determine the validity of this expected result that can be formalized as an analytical equation. These experiments will include contact angle measurements vs. drop size, area coverage and particle size (5 nm to 300 nm). Adhesion Experiments : Tilting experiments will be carried out to measure the a) advancing and receding contacts angles and b) the critical angle for drop movement, all as a function of the drop size and the characteristics of the textured surface (area fraction and particle size). Experiments will be carried out to determine the critical drop size that can still adhere to the surface when the substrate is held up-side down; these results will be related to an analytical equation that describes the critical pressure for spontaneous de-wetting.***

0103514兰格此提案是响应“纳米科学与工程”（NSF 00-119）的征集而提交的。只要液体在相同材料的平坦表面上的润湿角为90度，就可以通过产生类似于山丘和山谷的纹理表面来使表面成为超疏水或超亲水的。产生这种效果的机制是基于这样一个事实，即液体只润湿山顶，气体（空气）被困在山谷中。简单的分析功能已经开发了不同的周期性，纹理表面的润湿角有关的面积分数润湿的“山丘”和润湿角的平坦表面。荷叶是超疏水表面的天然例子。在1997年，微米大小的蜡块被发现产生这种效果。荷叶上的水滴几乎是球形的（q ~ 170度），很容易滚动，收集灰尘颗粒，产生自我清洁的效果，使莲花植物因其纯洁而受到尊敬。合成的超疏水表面已经通过在表面上涂覆“波纹状”薄膜和微成型方法产生。这些表面是有前途的实际应用，包括防雨表面，表面设计，以减少流体流动的阻力，和表面设计的选择性液体condensation.Recently，我们证明，超疏水表面可以通过简单地浸涂到一个包含小的，分散的颗粒浆料的基板。颗粒被吸引到基板上的相反的表面电荷，相对于基板。我们证明，面积分数和颗粒尺寸可以系统地控制，并且表面可以用在5 nm至300 nm范围内的化学上可用的颗粒进行纹理化。通过与氟烷基三氯硅烷分子的反应，一个平坦的表面呈现疏水性，和超疏水性，当texture.We观察到的超疏水效果是与吸附的二氧化硅颗粒的面积分数和超疏水效果消失时，球形颗粒之间的平均间距超过一个临界值。当颗粒非常小时，水滴显示出对表面的绝对粘附。后两种效应都可以用拉普拉斯方程来预测，该方程将弯月面的平衡曲率与水滴施加的压力相关联。系统的实验计划与纳米纹理表面研究这两个新的现象与特定的功能与拉普拉斯方程。这将使用将涂覆有胶态二氧化硅颗粒的玻璃基材来实现，所述胶态二氧化硅颗粒可商购获得，尺寸范围为5 nm至300 nm。所制备的纳米纹理表面将由玻璃衬底上随机分布的二氧化硅球组成。二氧化硅颗粒将通过烧结固定到基底上。然后，纳米纹理衬底将与氟烷基三氯硅烷分子反应，以确保最佳的疏水性。所有实验将在用相同氟烷基三氯硅烷分子处理的纳米纹理表面上用去离子水进行。有了这些约束，单位面积的表面能g和平面的接触角q将保持恒定。自发润湿实验：当拉普拉斯压力超过临界值时，将发生自发润湿，从而产生不稳定性;自发润湿预计是面积分数和颗粒尺寸的强函数。将设计实验以确定该预期结果的有效性，该预期结果可以形式化为分析方程。这些实验将包括接触角测量与液滴尺寸、面积覆盖率和粒度（5 nm至300 nm）。粘附力实验：将进行倾斜实验以测量a）前进和后退接触角和B）液滴运动的临界角，所有这些都是液滴尺寸和纹理化表面特性（面积分数和颗粒尺寸）的函数。将进行实验以确定当基底倒置时仍然可以粘附到表面的临界液滴尺寸;这些结果将与描述自发去湿的临界压力的分析方程相关。*