10 June 2015

Quinta Essentia

Lady's Mantle in the dye pot

Dyeing again. This time giving Lady's Mantle, Alchemilla, a whirl.

Not surprisingly it produces a yellow, so we shan't linger on the dyeing aspect.

Let's give some thought to those beads of water that linger on her leaves.

I'm sure you've noticed the beautiful diamond-like drops of water that collect on the leaves after rain or on a dewy morning.

Now, I could tell you the tale of how the alchemists of yore thought this crystal clear liquid was the Quinta Essentia, the very element from which the heavens are made; and from these hopeful, but sadly mistaken beliefs, Alchemilla derives her name.

But this blog has been lacking a certain scientific neutrality of late, so we'll go with the more technical exploration.

Lady's Mantle leaves are not just hydrophobic but superhydrophobic. This ability is also called the Lotus Effect, after lotus leaves that are similarly waterproof.

Distinct water droplets will form if the angle at the boundary where the water, solid surface and surrounding air meet is over 120 degrees.

This critical angle is likely to happen if the surface is uneven with little protuberances - like a hairy leaf. The water is then in what is called the Wenzel state.

However our superhydrophobic Alchemilla has protuberances on her protuberances.

These allow the water droplet to sit above the first layer of protuberances.

The water is in the Cassie-Baxter state, and can now just sit there looking all sparkly in the sunshine.


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