Technology for simple transfer of periodic microstructures developed by NIMS — Simply stick it on then peel it off

A research group led by Principal Researcher Kota Shiba at the Research Center for Macromolecules and Biomaterials of the National Institute for Materials Science (NIMS), in collaboration with the University of Connecticut, USA, has developed a method to easily transfer nanometer- and micrometer-scale periodic structures (periodic microstructures) formed on the surface of polydimethylsiloxane (PDMS), a common polymer material, onto a glass substrate. It is possible to design periodic microstructures with properties tailored to specific applications, such as volatility and structural coloring, which can have various applications. The results were published in the international academic journal Advanced Science on August 29.

Microstructures repeated at a regular interval on the nanometer-micrometer scale (periodic microstructure) have various applications depending on the size and repeating structure. The applications include water and oil super-repellency, water collection technology, antifogging, antireflection, sensing using structural color, and light-controlling metasurfaces. Lithography, which requires multistep processing, is currently used to form such structures. However, it exhibits issues such as equipment limitations, high cost, long time and multistep processing, and difficulty in application to large areas. Printed fabrication is also possible but presents other challenges, such as creating a master via lithography, selecting the ink type, and ink replenishment.

In response, the researchers considered development of a method that does not involve these issues. By performing oxygen plasma treatment to PDMS, a versatile and flexible polymer material, molded into a thin flat plate, a pillar-like periodic microstructure was formed on its surface. The researchers demonstrated that the periodic microstructure thus formed could be transferred onto a glass substrate by attaching it to the glass substrate and peeling it off. PDMS is typically used by mixing liquid PDMS with a hardener, molding it into desired shapes, and then curing it.

The degree of curing was adjusted in the newly developed method, intentionally leaving a large amount of liquid PDMS in the cured PDMS and successfully utilizing the oozing phenomenon of this liquid PDMS as an ink for structural transfer. As the ink is abundant inside the PDMS plate, it was confirmed that the same PDMS can be used multiple times for structural transfer without ink replenishment. Based on the amount of liquid PDMS remaining, it is believed that several thousand transfers are possible. PDMS is unstable in its liquid form, but the structure can be quickly stabilized via argon plasma treatment for approximately 10 s.

The transferred periodic microstructure depends on the structure of the PDMS surface. By controlling the surface structure of the involved PDMS, it is possible to adjust the spacing and size of the pillars and freely change the transferred periodic microstructure. As the area of the transferred structure depends on the size of the PDMS slab, area increment is expected to be easy. The researchers also confirmed that it is possible to add other components to the transferred periodic microstructure and that additives such as silicone oil and silica nanoparticles were present in the transferred structure. It was found that depending on the type of additives, the transferred periodic microstructures could be functionalized in various ways. Oxygen plasma treatment has been performed so far for the purpose of adhesion, and peeling has not been considered.

Shiba said, "This research began when an experiment that I was conducting for a completely different purpose failed. I am surprised and pleased as a researcher when I see that unexpected results (failures) have various developmental potentials. We would like to develop this technology into one that can be implemented in society."

Journal Information
Publication: Advanced Science
Title: Syneresis-Driven Self-Refilling Printing of Geometry/Component-Controlled Nano/Microstructures
DOI: 10.1002/advs.202405151