When playing on the beach, you can see mussels adhering to the rock from time to time, even if the rock surface is rough or even completely immersed in seawater, the mussels can still adhere firmly to the rock surface.
Based on the adhesion mechanism of mussels, scientists have worked tirelessly to develop shellfish biomimetic glue to achieve effective bonding on substrates that are wet on the surface, even in water.
Very early on, the author introduced Jonathan Wilker's research work "Shellfish biomimetic glue, to achieve super adhesion in water". Unfortunately, the high price of raw materials used hinders the widespread use of bionic glue.
Therefore, researchers from the Qingdao Institute of Bioenergy and Process Technology of the Chinese Academy of Sciences, Wuhan Institute of Technology and the University of the Chinese Academy of Sciences have jointly developed relatively low-cost shellfish bionic glue using different technical routes.
The core raw material of this glue is the low-cost commercial raw material polyvinyl alcohol (pva) as the main chain, and then grafted 3,4-dihydroxybenzoic acid (dhba) as a side chain.
Before grafting dhba, the two hydroxyl groups on dhba are protected with t-butyldimethylsilyl (tbs); after grafting, the tetrabutylammonium fluoride (tbaf) is used to remove the tbs that seal the hydroxyl group to obtain the final polymer pva-g-dhba.
Next, we will explain each key technical point one by one:
1. The grafting rate of dhba (dg value in the table below) can reach up to 10 mol%; the higher the grafting rate, the higher the bonding strength of the glue.
2. Pva-g-dhba as the main shellfish biomimetic glue needs to have a crosslinking agent to improve the bonding strength, while the commonly used crosslinking agent is trivalent iron ion; when the molar ratio of trivalent iron ion to dhba (catechol) is 1:3, the bonding strength of glue to glass reaches the highest value of 4 mpa. If there is no crosslinking agent during the curing process, the bonding strength of the glue to the glass is only about 1.2mpa.
The intersection of trivalent iron ions with pva-g-dhba is shown in the following figure:
3. In different bonding environments, bionic adhesives show different bonding capabilities for glass. When heated curing conditions at 60 °C, the glue reflects the highest bond strength of 4mpa, curing at room temperature is 1.5mpa; for wet glass, the bonding force drops to 0.5mpa; if the glass is bonded directly in water and cured in the whole process, the adhesive bonding strength of the glue is 0.2mpa.
The researchers believe that high-temperature curing helps to accelerate the oxidation of catechol, improve crosslinking, and thus improve the adhesion force; while the wet substrate and the substrate soaked in water, due to the interface between the glue and the substrate has a thin water layer of barrier, the adhesion force drops rapidly.
Nevertheless, researchers believe that the adhesion ability of this bionic glue in water is still stronger than that of commercial products on the market.
Reference Links:
https://doi.org/10.1002/macp.201700206.
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