What if a surface could instantly switch from sticky to slippery at the push of a button? By using electricity to control how ions and water structure at the solid liquid interface of self-assembled monolayers of aromatic molecules, researchers at National Taiwan University have created a molecular-scale adhesion switch that turns attraction on and off.
Why do some surfaces stick together while others repel each other? At scales far too small to see with the bare eye, this question is controlled by a complex interplay of intermolecular forces that arise when charged particles, called ions, and water organize themselves at the boundary between a solid and a liquid.
Understanding and controlling this behavior is essential for technologies ranging from lubricants and coatings to sensors and electronics.
In a study in the Journal of the American Chemical Society, Valentina Wieser, first author of the study, and colleagues at National Taiwan University used this structuring phenomenon to electrically switch molecular adhesion between a specifically designed aromatic surface adsorbent layer and a mica surface immersed in sodium containing electrolyte.
By adjusting the voltage applied on the gold surface beneath the molecules, the researchers were able to control where the ions moved and hence modulate the interaction between the molecules and the mica surface.
When negative potential was applied, positively charged sodium ions were directed into the molecule layer where the particular molecular structure kept them anchored. This led to the formation of a very stable, cushion-like barrier of ordered co-ions and water. As a result, the mica surface was strongly pushed away.
In contrast, when positive potential was applied, the cations were expelled out of the layer and the broadly structured ion and hydration layer at the interface collapsed, allowing the two surfaces to attract each other.
In effect, the researchers created an electromechanically controlled adhesion switch, a surface that becomes either repulsive or "sticky" solely depending on the applied voltage and the specific ion structuring.
This discovery shows how precise control of ions and water at interfaces can be used to design smart, responsive surfaces with switchable mechanical properties.
"This system shows a very peculiar mechanism for specific ion structuring and capturing that opens up fascinating new possibilities for understanding and utilizing interface phenomena," says Prof. Hsiu-Wei Cheng, co-corresponding author of the study.
To see article on Phys.org: https://phys.org/news/2025-11-electric-ions-enables-switchable-molecular.html