1 Why is it difficult to measure small contact angles using

1) Why is it difficult to measure small contact angles using the sessile drop method?  

2) Are there any trends in comparing the left hand measurements with the right hand measurements of the contact angle?

Solution

Ans 1

In sessile drop method, a fine clean platinum wire is used to form the droplet and it is

then placed on the surface of interest. For small contact angles, the deformation that

occurs during removing the wire affects the observation. Further the kinetic

energy associated with the flowing droplet also becomes a concern.

ans 2

Theoretically, the left hand measurements and the right-hand   measurements of

the contact angles should be same. However, in practice, it is found

that the advacing scenario gives a better accuracy in measurement

than the receding scenario.

the wetted length precisely. However, it is difficult to make these precise measurements

With recent development in technology, AFms are being successfully used to measure

small contact angles with high accuracy.