How Do You Determine the Tangent Point for Contact Angle in Droplet Analysis?

[Bystander]

Here in these pictures,direction of surface tension shows that it wants a flat surface.Does flat surface have smaller surface area than curved one?

Yes.

T1, and T2 are interfacial (surface) tensions between the solid and liquid (which is not wetting in the illustrated case), and the solid and air Respectively?

Yes.

After this correction of my picture will your answer be still same?

Yes. I think, not certain, the angle for T₃ is exaggerated. My suspicion is that T₃ will have a direction very close to that of T₂.

 

[gracy]

Sir,what is the direction of surface tension?Is it same as direction of contact angle?

Yes.

Sir,how?As angle has two directions,contact angle also has two directions.One is direction of the cohesive force and direction of the adhesive force.

 

[Bystander]

Direction for a surface or interface is going to be in the plane that is tangent to the interface. You've already seen that it has to be specified which two phases are in contact, solid-liquid, solid-vapor, liquid-vapor. The contact angle for total wetting is 0 degrees, total repulsion (water on waxed paper, mercury on glass) is 180 degrees, and this is for solid-liquid interfaces. Partial wetting contact angles indicate the angle between the air/vapor-liquid interface/surface, and the air-solid interface or surface.
Now, which of these is the cohesive direction, and which the adhesive direction?

 

[Bystander]

Adhesion: perpendicular to the solid surface, the force of attraction holding either the liquid or the vapor phase to the solid surface.
Cohesion: parallel (tangent) to the solid surface (the cohesion of the solid surface), or parallel (tangent) to the liquid surface (the cohesion of the liquid surface).

 

[gracy]

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Now, which of these is the cohesive direction, and which the adhesive direction?

Here T1=Force due to surface tension at the liquid-solid interface
T2=Force due to surface tension at the air-solid interface
T=Force due to surface tension at the air-liquid interface
All forces are adhesive.No cohesive force.Because the force of attraction between two molecules of the same substance is called cohesive force.