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
Newly discovered bacteria-binding protein in the intestine
08.12.2016 | University of Gothenburg
The balancing act: An enzyme that links endocytosis to membrane recycling
07.12.2016 | National Centre for Biological Sciences
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
08.12.2016 | Physics and Astronomy
08.12.2016 | Health and Medicine
08.12.2016 | Life Sciences