Surface preparation contact-angle test

Before actual bonding, the subjective water-break test or the quantitative and objective contact-angle test may be carried out. After bonding, the effectiveness of surface preparation may be determined by measuring the bond strength and determining the mode of the failure of the adhesive joint. 

Drops Deposited on Dirty Surfaces. We have implicitly assumed an ideal surface. On a real surface, the contact angle of a drop is often slightly dependent on the preparation conditions. Its value lies between two limits (larger) and 6 (smaller). The hysteresis of the contact angle, determined via the force 5 = 7 cos Or cos a), will be discussed in chapter 3. The difference 0a. is a measure of the state of cleanliness and roughness of a surface. It is used as a test in the automobile industry to ensure that surfaces are perfectly clean before applying paint. Oa Or must be sufficiently small for good adhesion. 

Thirdly, a water break test should then be carried out by spraying distilled or deionized water on to the prepared surface (Surface characterization by contact angles -polymers and Wetting and spreading). Careful abrasion is needed until a continuous layer of water remains for 30 s without any breaks. Once dried, the surface will then be ready for bonding. 

In the method applying thermodynamic instability, described in Section II, the critical condition at which the instability occurs is not so obvious because the movement of the three-phase line is slow. This method also has the disadvantage that a cone surface must be prepared for each test in order to measure contact angles. On the other hand, it is easier to recognize the... 

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