May. 19, 2019

Cassie extreme wetting impregnation

Researching petal roughness quickly brought me to that Cassie phrase.  Turns out that phrase isn't a very good description.  More often you will see the "Cassie-Baxter effect".  But it sure got attention, and led to a delightful moment of discovery.  Petal texture has to do with beading water, and the degree to which droplets are retained, or run off.  The interaction between water surface tension and petal roughness is the key.  Some types of roughness produce the petal effect, which keeps droplets from running away.  A common example is a rose petal, which droplets stick to even upside down.  Other types of roughness produce the lotus effect, which enables droplets to very easily run off, as with the common example of a lotus leaf.  A read of the "wetness" item in Wikipedia thouroughly explains all this.  And it quickly leads to words like superhydrophobicity and a plethora of mathematical formulae that mostly explain the difference between dabblers and true scientists.  And the dabbler still wonders if the reflection of light isn't also part of the story.