Theory of Adhesives and Adhesion

Adhesives are used in everyday applications. Adhesives may be in liquid form or thick pastes. Their main mechanism is based on the polymerization or crosslinking of polymers, which gives rise to glue or other adhesive application. The degree of adhesion of such a process is determined by conventional technological tests. 

What follows from Young s equation is that, if a liquid is removed from the surface of a solid, work will be needed, to execute this process (= Wad). This process will require the destruction of 1 cm2 of interface ySL, and the creation of 1 cm2 of y S and y L. From this we get 

This shows that, to remove a liquid from a solid surface, surface tension and contact angle 0 are required. If the liquid wets the solid surfaces (water on glass 0 = 0), 

Wad is thus the work needed to create twice the surface tension (one on each side after separation or breakup). 

Another area of much interest is the adhesion of ice to solids. This system is obviously of much interest in general everyday phenomena (tire friction on road surfaces, ice on metal surfaces, ships, etc.). Especially of interest is the adhesion of ice on ships sailing in the cold areas, and on wings of airplanes. Investigations have shown that the adhesive bonds between clean metal surface and ice are very strong. When the ice is removed by force, it breaks, leaving a thin layer of ice on the solid layer. 

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