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1、wetting hysteresis:the change in contact angle due to the hysteresis in moving of three-phase line of contact along the solid surface.2 wetting hysteresis(contact angle hysteresis)潤濕滯后潤濕滯后1)definition Fig.3-10 wetting hysteresiswetting hysteresis1 1 advancing contact angle:the contact angle when the

2、 non-wetting phase is displaced by wetting phase 2 2 receding receding contact angle:angle:the contact angle when the wetting phase is displaced by the non-wetting phase.2)2)Factors affecting contact angle hysteresis Surface roughness Adsorption of surface-active materials at the solid surface Rate

3、of fluid movement The saturation history Effect of the saturation history on contact angle hysteresisstatic contact angle hysteresis:The change in contact angle causing by the saturation history E B.Effect of rate of fluid movement on contact angle hysteresisFig.3-11 dynamic wetting hysteresis and i

4、nversion dynamic contact angle hysteresis:contact angle changes caused by moving speed.Fig.3-12 The relationship of contact angle and moving speedSpeed V (cm/s)Contact angle(degree)C.Effect of roughness D.Effect of adsorption of surface-active materials at the solid surfaceExample:when a clean solid rock contacts with oil for a period of time,surface-active materials in oil adsorpt at the rock surface,causing system that is initially water-wet to change to oil-wet.