Contact Angle wetting and nonwetting

1
Contact Angle wetting and non-wetting
? Is always measured through the aqueous phase

• For water drops on a surface
• 0 lt ? lt 90 Hydrophilic Surface-wets glass
  (glass, mica, platinum)
• 90 lt ? lt 180 Hydrophobic Surface (teflon,
  Rain-X on glass)

• For Rain-X on Glass
• Silicone compounds in the Rain-X chemically bond
  to the glass and causes the glass to become
  hydrophobic (causing water to bead-up on the
  glass).

2
Finger Printing-an example of hydrophobicity

• Vaporize a little Iodine carefully in a closed
  container. Use protective wear.
• The Iodine sublimes (turns from a solid into a
  gas) at room temperature but is enhanced with
  gentle heating (the melting point in 114C)
• Put your finger print on a strip of paper and
  insert this carefully into the container making
  sure not to inhale the vapors. Since Iodine is
  hydrophobic, the iodine will be attracted to the
  oil in your fingerprint and adsorb into that oil
  resulting in a visible fingerprint