Self-assembling... 'Nano Matchsticks' Creating Various Shapes

UNIST Professor Son Jaesung's Team Develops Inorganic Nano Matchsticks Friendly to Both Water and Oil

Synthesis process and images of silver sulfide-cadmium sulfide nano surfactants.

[Asia Economy Yeongnam Reporting Headquarters Reporter Hwang Dooyul] A technology has been developed in which matchstick-shaped nanomaterials self-assemble to create various shapes.

The developed nanomaterials are attracting attention because they can form diverse structures even in materials larger than molecules, similar to molecular structures.

Professor Son Jaesung's team from the Department of Materials Science and Engineering at UNIST recently succeeded in fabricating a matchstick-shaped "silver sulfide (Ag₂S)-cadmium sulfide (CdS) inorganic nano surfactant."

By adjusting the hydrophilicity and hydrophobicity of the material's surface, various shapes of self-assembled structures can be created.

The material can reproduce the structural diversity previously seen in "molecular-type surfactants" at the nanoscale.

A property where a material possesses both hydrophilicity and hydrophobicity is called "amphiphilicity." Surfactants used in soaps and detergents are typical examples.

Usually, amphiphilic materials hide the parts with low affinity depending on the solvent characteristics. This lowers the energy at the boundary, enabling self-assembly, which is known as an effective technique for creating materials with regular structures.

However, molecular-type amphiphilic materials are too small to have certain functions.

Therefore, only the advantages of their unique structures could be utilized, but recently, many studies have aimed to create nanoscale amphiphilic materials with specific functions by introducing charged "hydrophilic surface treatments."

The goal is to create functional materials larger than molecules that can self-assemble by changing the surface properties of "functional inorganic nanomaterials" shaped like balls or dumbbells.

(From left) First author researcher Koo Dahwi, co-author researcher Choi Wooyong, corresponding author professor Son Jaesung.

First author Koo Dahwi, a combined master's and doctoral course researcher in the Department of Materials Science and Engineering at UNIST, said, "Nanomaterials shaped like balls or dumbbells have been difficult to reproduce the diverse structures seen in molecular-type amphiphilic materials because controlling the aspect ratio was challenging. In this study, we synthesized nanomatchsticks with a high aspect ratio and fabricated inorganic nano surfactants through a selective ligand exchange process based on the HSAB (Hard Soft Acid Base) theory."

The newly developed nano surfactant consists of a "hydrophilic head" and a "hydrophobic long stem."

Using this amphiphilicity, it is possible to organize into liquid droplets or specific self-assembled structures. It was also demonstrated that by adjusting the aspect ratio and surface amphiphilicity, structures such as curved surfaces, wrinkles, and cylindrical shapes can be selectively self-assembled.

Professor Son Jaesung emphasized, "Nano surfactants with a high aspect ratio have enabled the fabrication of a wider range of functional nanostructures that were impossible to realize with conventional ball-shaped or dumbbell-shaped materials. The ability to control structures vertically is an excellent technology that expands the structural diversity of nano surfactants."

The research was published as a supplementary cover paper in the October issue of the prestigious journal "JACS Au," published by the American Chemical Society.

The study was supported by the Korea Research Foundation's Mid-Career Researcher Support Program, the Challenging Materials Technology Development Program, and the Global PhD Fellowship.

JACS Au October 2022 Issue Inside Cover.

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