The Research Of Relationship Between Droplets Evaporation On The Hydrophobic Surface And Its Contact Angle

Through a series of comparative experiments，this article observe the different kindsand volume of the droplets evaporation process on the different contact surface under thedifferent temperature. Through the experiment conclusion, the dynamic characteristics ofdroplets evaporation process are different on the different contact surface. Water dropletson the PDMS coating show a good hydrophobic. The static contact angle is120°.Therefore the PDMS coating belongs to the hydrophobic materials.There are two stage during the water droplet evaporation: in the first stage, dropletsolid-liquid contact diameter remains constant, the CA decreases nonlinear continuously; inthe second stage, when the contact Angle decreases to a certain angle, the droplets shapechange suddenly, Solid-liquid interface diameter instantaneously reduce to a certain fixedvalue, and will keep constant or slightly decreased in the later period of evaporationprocess,at the same time, CA suddenly increase to a certain value then continuous decreasegradually during the re-evaporation, until appear the second and another jump appearance.This paper define the contact diameter constant state as locked state, the first locked statetime is70%of the whole evaporation time.On the basis of experiment, through theoretical analysis and formula derived, thispaper obtained the equation associated with the θ1、r1、r2and the equation associated withmass flow rate and contact angle in the first locked state when water droplets evaporate onthe PDMS coating. By calculating, the two equations’ calculated value coincided basicallywith the experimental conclusions.This article has carried on the experiment research to find the relationship betweenwater droplets hysteresis resistance and contact angle on the PDMS coating. The dropletsneed to overcome the resistance is spreading work. Water dynamic advancing angle andreceding angle are smaller in comparison with their respective critical state.At last, this paper summarizes the relations among the surface free energy, surfacetension and contact angle, analyses the effect of surface free energy to the liquid dropletsshape and contact angle. Expand the relationship between the surface free energy and thecontact angle, reasonably explain the practical problems in the process of water dropletevaporation.