When gluing things together, both surfaces usually need to be dry. Gluing wet surfaces or 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 has chosen a different approach: they have moved away from natural models—and achieved reversible underwater adhesion.
The primary challenge for conventional adhesion under water is that the water molecules between the surfaces to be glued and the adhesive need to be removed so that these surfaces can react chemically. This is not the case with the new approach. Kim and his co-workers use host–guest interactions between water-soluble host molecule with a hydrophobic pocket and ionic guest molecule with a hydrophobic block. They form robust noncovalent bonds in water. In fact, the repulsion of water molecules is the driving force for formation of the bond, mediated by ion–dipole and hydrophobic interactions.
The researchers chose curcurbituril as their host and aminomethylferrocene as the guest. Cucurbit[n]uril (n = 5,6,7,8 and 10) are macrocycles—large, ring-shaped molecules made of multiple glycoluril units that can bind other molecules within their cavities. Their name is derived from cucurbita, the Latin name for pumpkin, which they resemble in shape. Ferrocenes are also known as sandwich compounds. The "bread" consists of two aromatic rings of five carbon atoms, while the "filling" is a single iron atom held in the middle. The ferrocene chosen by the researchers lodges very securely and specifically inside a "pumpkin" made of seven glycoluril units.
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 x 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. This is more than double-sided sticky tape can hold.
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. In comparison, the mussel mimetic underwater adhesives require strong oxidizing agents for curing to these applications, which is not the case with the new system.About the Author
Author: Kimoon Kim, Pohang University of Science and Technology (Republic of Korea), http://css.postech.ac.kr/
Title: Supramolecular Velcro for Reversible Underwater Adhesion
Angewandte Chemie International Edition, Permalink to the article: http://dx.doi.org/10.1002/anie.201209382
Kimoon Kim | Angewandte Chemie
New Technique Maps Elusive Chemical Markers on Proteins
03.07.2015 | Salk Institute for Biological Studies
New approach to targeted cancer therapy
03.07.2015 | CECAD - Cluster of Excellence at the University of Cologne
Wind turbines could be installed under some of the biggest bridges on the road network to produce electricity. So it is confirmed by calculations carried out by a European researchers team, that have taken a viaduct in the Canary Islands as a reference. This concept could be applied in heavily built-up territories or natural areas with new constructions limitations.
The Juncal Viaduct, in Gran Canaria, has served as a reference for Spanish and British researchers to verify that the wind blowing between the pillars on this...
New technique combines electron microscopy and synchrotron X-rays to track chemical reactions under real operating conditions
A new technique pioneered at the U.S. Department of Energy's Brookhaven National Laboratory reveals atomic-scale changes during catalytic reactions in real...
Think of an object made of iron: An I-beam, a car frame, a nail. Now imagine that half of the iron in that object owes its existence to bacteria living two and a half billion years ago.
Think of an object made of iron: An I-beam, a car frame, a nail. Now imagine that half of the iron in that object owes its existence to bacteria living two and...
A team of scientists including PhD student Friedrich Schuler from the Laboratory of MEMS Applications at the Department of Microsystems Engineering (IMTEK) of...
The three-year clinical trial results of the retinal implant popularly known as the "bionic eye," have proven the long-term efficacy, safety and reliability of...
25.06.2015 | Event News
16.06.2015 | Event News
11.06.2015 | Event News
03.07.2015 | Press release
03.07.2015 | Agricultural and Forestry Science
03.07.2015 | Health and Medicine