When water freezes on the surface of rock, metal, plastic and many other materials, it can be very difficult to remove. What makes the bonds so strong? What materials bond most strongly with ice?
• The strength of the bond depends on the roughness of the material. Fingers of ice grow into the cracks and irregularities on the surface of the contact material. The more cracks, the stronger the bond.
For example, glass is smooth, so although bonding is strong enough for ice to remain on vertical panes, it is easily lifted off in fairly large sheets. On wood, the ice bonds are strong enough to break the wood itself.
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Brian King, Barton on Sea, Hampshire, UK
• The strength of ice adhesion depends on the chemical composition of the surface. Water molecules are electrically polarised so adhere more readily to materials that are attractive to polar substances, such as metal and rock, through hydrogen bonding, and electrostatic and van der Waals forces. Non-polar materials, such as hydrocarbon plastics, are less attractive so ice shears more easily from them.
Ice can cause problems for aircraft, shipping and wind turbines. The aviation industry spends a fortune spraying planes with de-icing fluid in wintry weather, so there is a demand for a permanent solution. For example, researchers led by Joanna Aizenberg of Harvard University are working to create porous, liquid-infused surfaces that effectively flatten the surface at the nanoscale level and make it very difficult for ice to stick.
David Muir, Edinburgh, UK
• We often attribute stickiness to glue, but it can also be achieved by maximising the surface area of a material. Many insects rely on the same mechanism to cling to a vertical surface. Minuscule hairs on their feet create the largest area possible and friction between the hairs and the surface does the rest of the work.
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