Research The Dynamic Wetting Effect And Its Corresponding Dynamic Contact Angle Based On The Laser Reflection Method

Optical method is important to research the dynamic wetting of solid-liquid contact.The dynamic contact angle is the main physical parameter of solid-liquid contact,and it also is another reflection of wettability during solid-liquid contact.In our experiment,when an expanded and collimated laser beam impinges on the dynamic curved liquid surfaces at glancing incidence,the special reflection patterns,which can obtain the information of the dynamic contact angle and the changes of the curved surface,are observed.Based on the relevant knowledge of physical chemistry of surfaces,We present a method of optical measurement of the dynamic wetting,the dynamic contact angles and the changes of the dynamic curved liquid surface corresponding to dynamic wetting.This research method provides not only the theoretic bases for studying the dynamic wetting by optical method in real time,but also the experimental basis for measuring the dynamic contact angle by optical method in real time.The main researches are summarized as follows:(1)According to the physical chemistry of surfaces knowledge,the changes of the liquid surfaces during the solid contact with the liquid and the measurement of the dynamic contact angle are discussed,and the dynamic wetting are analyzed.It provides a theoretical basis of the feasibility of laser reflection for study the dynamic wetting effect.(2)A novel dynamic contact angle measurement by laser glancing incidence method.When an expanded and collimated laser beam impinges on the dynamic curved liquid surfaces at glancing incidence,the special reflection patterns,which corresponding to the different states of the dynamic wetting,are observed.The reflection patterns fall into three types:First,the pattern contains a dark central region and a bright field outside.The shape of the dark field is close to an ellipse.Clear fringes,like single edge diffraction,are observed near the boundary between the dark and bright field.The reflective light intensity that results from up curved surface;the second reflection pattern is split into two parts:One part of the reflection pattern contains a dark central region and a bright field outside.The shape of the dark field is close to an ellipse.Clear fringes,like single edge diffraction,are observed near the boundary between the dark and bright field,and the other part contains the bright central region and a weaker field outside.The fringes can be observed in the central range;Finally,the reflection pattern contains the bright central region and a weaker field outside.The fringes can be observed in the central range.The reflective light intensity that results from down curved surface.Using geometric optics and the Wilhelmy plate method,the relation of the critical height of the up-curved liquid surface and the dynamic contact angle is simply derived.And the relation of the critical depth of the down-curved liquid surface and the dynamic contact angle is simply derived.and The dynamic contact angle of dynamic curved liquid surface is calculated directly by measuring the dark/bright field width of the reflection pattern.(3)The characterization of the dynamic curved liquid surface corresponding to dynamic wetting of the rod.Using the critical light reflection from dynamic curved liquid surfaces due to the dynamic wetting,study changes in dynamic curved liquid surfaces.When a rod is vertical immersed into liquid water and then withdrawn out at a constant speed.The liquid around the rod climbs up the rod at first,then one part of liquid surface from up-curved become down-curved;another part of liquid surface still up-curved but the critical height declined.Finally,the liquid surface becomes curved down with the depth of the immersing rod.when a rod is withdrawn out vertically of liquid water at a constant speed,the liquid surface curved down at first,then the liquid surface becomes curved up with the height of the withdrawing rod.When an expanded and collimated laser beam impinges on the dynamic curved liquid surfaces due to the dynamic wetting at glancing incidence,the special reflection patterns,which from dynamic curved liquid surfaces,are observed.When a rod is vertical immersed into liquid water and then withdrawn out,the special reflection patterns will change with the surface deformation.Then the two-dimensional dynamic curved liquid surface profiles are calculated numerically by Runge-kutta method MATLAB software.(4)We present a method of optical measurement of the dynamic wetting,the dynamic contact angles and the changes of the dynamic curved liquid surface corresponding to dynamic wetting.This method has the property of accurate,real-time and non-destructive,and this method is particularly suitable for measurement of single fiber contact angle.