Most adhesives have excellent adhesive strength in air and quickly lose their effect in water because of the hydration/swelling/degradation of adhesive molecules as water molecules enter the adhesive interface. Rapid loss of adhesive properties. Therefore, underwater high-adhesion materials have always been the research difficulties and hotspots in the field of engineering materials. Researchers have developed different types of underwater adhesive materials through biomimetic dopamine, interfacial supramolecular interactions, and polyelectrolyte complexation, but it is difficult to achieve the control of underwater reversible adhesion.
Recently, the team of Zhou Feng of the Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, teamed up with the Wang Dingkai Group of the City University of Hong Kong to design and prepare a bionic underwater "glue". The material not only has strong adhesion under water, but also Importantly, its adhesion strength under water can be reversibly adjusted by controlling the interface temperature.
The material system design concept stems from the high adhesive strength of underwater mussels under water and the rapid failure of underwater adhesives. In order to make the material have high adhesion under water, the researchers first prepared an underwater adhesive polymer, that is, the adhesion of dopamine molecules with hydrophobic monomers to prepare biomimetic adhesive linear polymer; In order to achieve the underwater adhesion strength Adjustability, and also designed to prepare a temperature-responsive polymer (poly-N-isopropylacrylamide), which forms an intermolecular hydrogen bond with water molecules at a lower temperature than its phase transition temperature. The state of formation, when it is above its phase transition temperature, forms an intramolecular hydrogen bond and assumes a dehydrated state. Therefore, according to the principle of underwater adhesive failure, this responsive molecule is covered on the surface of the adhesion molecule. By adjusting the temperature and adjusting the hydration and dehydration of the molecules at the interface, reversible regulation of underwater adhesion can be achieved.
In order to enable the smooth and homogeneous assembly of the responsive molecules onto the surface of the viscous polymer, the supramolecular host and guest were introduced into the above two polymer systems, and the efficient assembly of the responsive polymer on the surface of the adhesive polymer was realized through molecular recognition. The mechanism of underwater adhesion strength adjustment of this material system is shown in Figure 1. The micro/macro adhesion test confirms that the surface of the material has a higher water-based adhesive strength at higher temperatures and almost no adhesion at room temperature. This high adhesion-low adhesion strength transition allows for reversible adjustments with little loss of its underwater adhesion strength (Figure 2).
In addition, the material has the following advantages: Without the limitation of the substrate material, it has the reversible regulation performance of the underwater adhesion strength on the surface of various materials; the adhesion strength of the material can be improved by increasing the surface roughness; and the composition of the thermosensitive polymer can be changed by adjusting the temperature. The lowest phase transition temperature enables the adjustment of the temperature transition point of the adhesive strength.
The related research results were published on Nature Communications under the title of Bio-inspired reversible underwater adhesive. The research work was supported by the National Natural Science Foundation of China, the Hong Kong Research Foundation, the National Key Research and Development Program, the Chinese Academy of Sciences, the Shenzhen Science and Technology Bureau and the City University of Hong Kong. stand by.
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