text: Contact angle, or wetting angle, is a very important parameter in real systems where perfect wetting ( = 0) is hardly ever achieved.  The Young equation provides reasoning for contact angle involvement in capillary condensation.  The Young Equation explains that the surface tension between the liquid and vapor phases is scaled to the cosine of the contact angle.  As shown in the figure to the right, the contact angle between a condensed liquid and the inner wall of a capillary can affect the radius of curvature a great deal.  For this reason, contact angle is coupled inherently to the curvature term of the Kelvin equation.  As the contact angle increases, the radius of curvature will increase as well.  This is to say that a system with perfect wetting will exhibit a larger amount of liquid in its pores than a system with non-perfect wetting ( > 0).  Also, in systems where  = 0 the radius of curvature is equal to the capillary radius.  Due to these complications caused by contact angle, scientific studies are often designed to assume  = 0.