Supramolecular Velcro for Underwater Adhesion
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Gluing wet surfaces or even surfaces under water is a challenge. In the journal Angewandte Chemie, Korean scientists have now introduced a completely new concept. They were able to achieve reversible underwater adhesion by using supramolecular “Velcro”.
Previously, researchers have primarily attempted to mimic natural underwater “adhesives” like the adhesive molecules used by mussels. Such substances adhere well in wet surroundings, but the adhesion is not reversible. A team led by Kimoon Kim at Pohang University of Science and Technology in Korea uses so-called host-guest interactions between water-soluble host molecules with a hydrophobic pocket and ionic guest molecule with a hydrophobic block, which form robust noncovalent bonds in water. The repulsion of water molecules is the driving force for formation of the bond.
The researchers produced some silicon strips with many “pumpkins” attached, as well as some with many “sandwiches”. When these strips come into contact with each other they stick together tightly, similar to Velcro. Once stuck together, a 1 × 1 cm piece of this supramolecular Velcro can hold a weight of 2 kg in water. After drying in air it can hold as much as 4 kg.
Like a macroscopic Velcro strip, the molecular version can be separated with a strong pull and reused multiple times. The adhesion can also be reversed chemically through application of a hypochlorite solution, which oxidizes the iron atoms. After reduction with an agent such as ascorbic acid, the Velcro can adhere again. Because the materials used are biocompatible, biological applications may be possible, for example in surgery suture or repairing live tissue. Mussel mimetic underwater adhesives are not suitable here, as they require strong oxidizing agents for curing.