Surface Tension and Contact Angle A First Look

2 SURFACE TENSION AND CONTACT ANGLE A FIRST LOOK 6.2a Surface Tension as a Force 

2 Illustrations of liquid film formation, contact angle, and measurement of contact angle (a) a wire loop with a slide wire on which a liquid film might be formed and stretched by an applied force F. (b) profile of a three-phase (solid, liquid, gas) boundary that defines the contact angle 0. (c) the tilted plate method for measuring contact angles. 

Several points should be noted before proceeding any further  

Equation (1) defines the units of surface tension to be those of force per length or Nm 1 in SI or dynes cm 1 in the cgs system. We see presently that these are not the only units used for 7. 

A gas in the frictionless, three-dimensional equivalent to the apparatus of the figure would tend to expand spontaneously. For a film, however, the direction of spontaneous change is contraction. 

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