Hysteresis in contact angle measurements

What are the possible reasons for hysteresis Various explanations for contact angle hysteresis have been discussed. The contribution of each factor depends on the particular situation encountered. Possible causes of hysteresis are  

With 7 = 0.072 Nm-1 and 5 = 10 nm the effective pressure is of the order of P = 72 x 10s Pa. Such a high pressure can change the surface structure, cause mechanical deformation at the moving wetting line [250], and can lead to contact angle hysteresis [251-253], especially on soft polymer surfaces. 

A very important factor is the length scale of surface structures and their shape. This becomes obvious when looking at the spreading of a liquid on surfaces with a micropatterned heterogeneity [246,258,259], 

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