Thursday, 14 February 2013

Snow, Sledding, Superhydrophobic Properties and Avalanches

Last Tuesday was Pancake day or Laskiaistiistai  in Finland which precedes Ash Wednesday.  It is usually the on the second week of February and in Finland it is a day where kids go outside to sled and hangout in the snow.  This could be good with a superhydrophobic coating and bad if their were the off chance of an avalanche. In both cases surface tension is a contributing factor since it involves frozen water.    


Making a Faster Sled

However, this snow day could become dangerously awesome if a superhydrophobic coating from Ultraeverdry was applied to the bottom of a sled.  (This has the Dudesons written all over it).  The super hydrophobic coating repels water and makes the bottom have less friction.  Waxing does the same.  However, the spray coating from is both superhydrophobic (repelling water like a lotus leaf with a high contact angle) and quite oleophobic (lacking affinity for oils).  This makes it quite different than wax. 

On a microscopic level the nanomaterial is rough working like the Lotus effect to repel droplets so it is easier for the droplets to maintain their shape with the help of surface tension than it is to wet the surface.  One interesting thing about the nanomaterial is that it prevents icing too.  However, it probably won't be used for sledding as it is both toxic and expensive.


If one is using this material and going down the hill this fast it could cause an avalanche.  This is the case in Luckily, in Finland they have little chance of avalanche (not lucky if you like the mountains).  Avalanche are caused by the different levels of the snow changing their properties so one level might be hard packed but the upper level is soft packed and loose.  Snow grains are held together by surface tension and air bubbles. 

Wet snow grains held together by surface tension from Juneau Empire

If there is unusually warm air or rain it likely will only affect the top pack of snow.  As more water trickles down through the snow grains are not bound together by air bubbles and the water's surface tension but rather just suspended in the water.  This causes the top snow pack to lose its strength and with some sort of small force like Clark W. Griswold going down the hill on a superhydrophobic sled at super fast speeds this  could cause an avalanche (of one of the different kinds shown in the picture).