Study On The Effect Of Pressure On The Wettability Of Solid Surface

Nature is an inexhaustible source of functional surfaces. Since millennia, plants and animals have developed surfaces with special wettability ranging from very high slippery to high sticky surfaces. The wettability plays a key role in many applications which decides the ability of the liquid on the surface, such as adsorption, spreading, permeability and hydrophobic or hydrophilic. At present, the contact angle testing has become the most convenient and accurate access to obtain the wettability of the surface. The contact angle is the angle, conventionally measured through the liquid, where a liquid/vapor interface meets a solid surface. It quantifies the wettability of a solid surface. People used to take θ=90°as boundary to determine whether the wetting happens. Wetting deals with the three phases of materials:gas, liquid and solid and it is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together, so the theory and application on the wettability of solid surface are studied thoroughly.There are many kinds of methods about the measurement of contact angle, these methods continue to improve. Angle measurement method has become the most extensive characterization methods, due to the small size of the sample, no pollution to the surface, no requirement for liquid type, the advantages of simple operation and convenient access to data. Some problems have been plaguing researchers, for example, the measurement results under the influence of operator and needle brings interference on measurement results when the characterization of surface advancing and receding angles. At present, there is no effective method to solve this problem without damaging the surface. The wettability of solid surface about the effects of the surface chemical composition, micro structure and environmental factors has been in-depth studied. But the effect of pressure on surface wettability is still in the initial stage. At the same time, these studies seldom used in the surface of nanometer scale. In this paper, we independently designed a device of measuring droplet contact angle, roll angle, advancing and receding angle under controlled temperature, humidity and pressure. Then, we propose a testing method for the contact angle in order to eliminate the interference of the needle. After that, We discussed the application of characterizing the surface energy on polymer material surface with captive bubble method. At last, under the condition of definite pressure and humidity, different diameters of the wetting state of nano-porous surface are investigated. The main achievements and innovations of this thesis are:(1) We independently designed a device of measuring droplet contact angle, roll angle, advancing and receding angle under controlled temperature, humidity and pressure. It is suitable in a wide range of temperature and humidity along with a high or negative pressure system. The devices which can prevent glass window surface fogging at low temperature are equiped. The high speed camera (1400000 fps) can real-time track of the process of the water droplet freezing or bouncing on the super hydrophobic with low temperature.(2) A contact angle test method was proposed. The test device was improved by adding the key components of environmental pressure chamber. By controlling the pressure of environmental chamber pressure, the bubble volume was changed so as to achieve the accurately testing of the advancing and receding angles. This method eliminates the interference between the needle and the bubble which makes the bubble shape distortion in the traditional method. In this paper, the advantages of this method were discussed on the aspects of measuring precision, relative error and the rang of application filed. A more reliable and high repeatable test method was provided for the characterization of the surface wettability.(3) The contact angle measurement method was used in the solid surface energy testing. The common polymer surfaces were as the test object including PMMA plate, polyethylene plate and PE plate. The ethylene glycol, glycerol, diiodomethane, deionized water and cyclohexane were used as the testing solvent and the testing results of surface energy demonstrated the advangtage of this method while using the volatile solvent. The application conditions on the data analysis with Owens-Wendt-Kaelble method and Lifshitz-vanderWaals acid-base method were discussed. This discussion provided a theoretical basis on the solid surface energy test in the future.(4) The anodized aluminum plate of different nano pore diameter were prepared successfully through the anode electrolysis technology and these plate were treated with PFO of low surface energy and APTS of the high surface energy. The wetting state changes of the nanoporous structure on static or dynamic impact pressure were studied systematically. It reveals the irreversible of the transformation of the wetting state and the instability of the wetting state under different pressure conditions. The spontaneity of the transformation of the wetting state on hydrophilic surface was verified. At last, we pointed out the difference between nano scale and micro scale on the critical pressure of the surface wetting state completely changed.