Other reasons for contact angle hysteresis

Hysteresis due to molecular orientation and deformation on solid surfaces 

The advancing and receding contact angle values may decrease with decreaseing drop size (or in the captive bubble method, with the size of the bubble). This decrease is more pronounced in 0, values than in 0a. 

Since gravity effects are neglected for small drops, a possible explanation is the presence of the negative line tension. Gibbs was the first to postulate the line tension concept. He pro- 

The modified Cassie-Baxter equation was successfully used to interpret some of the contact angle data reported for heterogeneous surfaces. 

When liquid molecules are adsorbed onto a solid surface, their surface concentration will be a function of the distance along the solid, and of time, in a band close to the three-phase contact line. Consequently, there will also be a corresponding gradient of surface free energy density, which will directly affect the horizontal component of force at the three-phase line resulting in contact angle hysteresis. 

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