第2章-表界面原理2-温泽和凯西

2.1.3 Contact angle, wetting, and spreading
Cassie （凯西）State exists when a drop sits on and the voids between the asperities or topological features are filled with air resulting in a hydrophobic condition. 凯西模型指的是，液体位于表面上时，凹槽被空气填充，从而形 成疏水效果。
2.1.3 Contact angle, wetting, and spreading
Wenzel（温泽） State exists when the liquid of a drop fills the voids in the solid on which it sits.
温泽模型中，液体填满固体表面所有的凹槽结构。
2.1.3 Contact angle, wetting, and spreading
新的模型！（液滴足够大） Some years ago it was proven that the equations developed intuitively by Wenzel, Cassie and Baster are good approximations for the most stable CA if the drop size is sufficiently large compared with the scale of roughness or heterogeneity.
2.1.3 Contact angle, wetting, and spreading
The apparent contact angle is defined by Cassie's formula which includes a variable to account for the percentage of surface under the liquid drop is in contact with the solid. 存在凯西方程，其中一个变量涉及液体和表面接触面积的百分比 。
2.1.3 Contact angle, wetting, and spreading
Wenzel state breaks down at large r ⇒ air trapped within the surface roughness ⇒ Cassie State
温泽模型在较大粗糙度时失效，因为空气会在凹槽中形成气垫。
30℃
60℃
Science 2003, 299, 1377
Angew. Chem. Int. Ed. 2002, 41, 1221
2.1.3 Contact angle, wetting, and spreading
Self Cleaning Materials
迟力峰教授 1982年毕业于吉林大学物理系， 1989年于在德国Goettingen大学获博士学位， 1990至1993年在德国美因兹大学和BASF公司从事博士后研究。 2004年起任德国明斯特大学物理系教授。 2003年之2011年任吉林大学超分子材料与结构国家重点实验室双聘 教授。
2.1.3 Contact angle, wetting, and spreading
2.1.3 Contact angle, wetting, and spreading
2.1.3 Contact angle, wetting, and spreading
Transformation of a Simple Plastic into a Superhydrophobic Surface Super Hydrophobic Surface of Aligned Polyacrylonitrile Nanofibers
2.1.3 Contact angle, wetting, and spreading
Conventionally, super-hydrophobic surfaces have been produced mainly in two ways:
两种制作超疏水表面途径：
Create a rough surface
第二章——毛细现象 和表面动力学2
李硕琦 山东科技大学材料学院 2015.3
2.1.3 Contact angle, wetting, and spreading
应当指出，杨氏方程的应用条件是理想表面，即指固体表面是组 成均匀、平滑、不变形(在液体表面张力的垂直分量的作用下)和 各向同性的。然而实际上这种理想平面是不可能存在的，因此在 考察表面的润湿性时，需要考虑表面的粗糙度。
2.1.3 Contact angle, wetting, and spreading
According to Wenzel's formula, a roughness variable is used to account for the increased surface area which results in higher contact angles on superhydrophobic solids. 用粗糙度解释表面积增加所导致的超疏水表面。
Fig. 2 Schematic representation of: (a) duplication process and (b) iCVD reactor.
ቤተ መጻሕፍቲ ባይዱ
Mustafa Karaman , Nihat Çabuk , Demet Özyurt , Özcan Köysüren Self-supporting superhydrophobic thin polymer sheets that mimic the nature's petal effect Applied Surface Science, Volume 259, 2012, 542 - 546 /10.1016/j.apsusc.2012.07.079
2.1.3 Contact angle, wetting, and spreading
Wenzel’s equation shows that microstructuring a surface amplifies the natural tendency of the surface. 温泽模型显示，表面微结构会放大表面的亲水或疏水倾向。
θ is the Young contact angle as defined for an ideal surface.
2.1.3 Contact angle, wetting, and spreading
Wenzel方程表明，粗糙表面的存在使得实际上固-液的接触面要大 于表观几何上观察到的面积，于是在几何上增强了疏水性（或亲 水性）。即: θ<90°时，θ*随着表面粗糙度的增加而降低，表面变得更亲水; θ>90°时, θ*随着表面粗糙度的增加而变大，表面变得更疏水。
2.1.3 Contact angle, wetting, and spreading
液固实际接触面积比完美的平面大。 所以需要对杨方程进行修正。
温泽模型公式的推导
BEA Confidential. | 7
2.1.3 Contact angle, wetting, and spreading
where θ * is the apparent contact angle which corresponds to the stable equilibrium state. The roughness ratio, r, is a measure of how surface roughness affects a homogeneous surface. The roughness ratio is defined as the ratio of true area of the solid surface to the apparent area.
粗糙表面（还需要防止桃皮效应）
Modify the surface with materials of low surface free energy, such as fluorinated or silicon compounds. 低表面能物质薄膜
2.1.3 Contact angle, wetting, and spreading
2.1.3 Contact angle, wetting, and spreading
式中f 为水与固体接触的面积与水滴在固体表面接触的总面积之 比。 θ1固有接触角
θc*表观接触角
2.1.3 Contact angle, wetting, and spreading
This implies that with a small f and a large θ it is possible to create surfaces with a very large contact angle. 大的表观接触角需要较小的 f和较大的θ。
BEA Confidential. | 18
BEA Confidential. | 19
Fig. 1 SEM figures of: (a) fresh and (b) dry rose petal surfaces. Below the figures are the photographs of 5 μL water droplet s over the flat (left) and 90° tilted (right) surfaces.
Mustafa Karaman , Nihat Çabuk , Demet Özyurt , Özcan Köysüren Self-supporting superhydrophobic thin polymer sheets that mimic the nature's petal effect Applied Surface Science, Volume 259, 2012, 542 - 546 /10.1016/j.apsusc.2012.07.079
2.1.3 Contact angle, wetting, and spreading
Cassie's research pointed out that the water repelling quality of ducks is due to the very nature of the composite formed between air and feather and not by other causes such as the presence of exceptional proofing agents like oils. Water striders also exploit this phenomenon. Artificial superhydrophobic materials such as nanopin film exist in the laboratory that also make use of this law.
2.1.3 Contact angle, wetting, and spreading
研究人员发现，水黾的腿能排开300倍于其 身体体积的水量，这就是这种昆虫非凡浮力 的原因。水黾的一条长腿就能在水面上支撑 起15倍于身体的重量而不会沉没。而油脂层 和水表面的张力却没有如此大的浮力。
Contact angle hysteresis is greatly increased in the Wenzel state, decreased in the Cassie. 接触角的滞后现象在温泽状态容易发生，在凯西状态不易发生 。