Reviewed by Lexie CornerMar 3 2025
A research team led by Dr. Jeong Gon Son of the Korea Institute of Science and Technology and Professor Yongtaek Hong of Seoul National University has developed a stretchable substrate with nanostructure alignment that significantly reduces Poisson's ratio.
(Top) Distortion problems in elastomeric materials during stretching and distortion-free stretching. (Bottom) Typical elastomer with Poisson's ratio of 0.5 (severe vertical contraction, left), and aligned fiber composite for controlling Poisson's ratio near 0 due to the high stiffness of fibers resisting vertical contraction under strained states (right). Image Credit: Korea Institute of Science and Technology
Stretchable display materials, which are increasingly popular in next-generation displays, offer the benefit of flexibility. However, current materials often suffer from issues like screen distortion and poor fit.
The "Poisson's ratio" effect, which causes the screen to shrink vertically when stretched in one direction, makes elastomeric substrates prone to screen distortion.
Wearable technology and other electronics that are in close contact with the skin are particularly affected. The stretching and contracting of these materials can cause wrinkles or pull on the skin, leading to poor fit and performance.
To address these issues, the researchers combined two key concepts. They used block copolymers to align the internal nanostructures. The block copolymer, made of rigid “polystyrene” (PS) and softer “polybutylene” (PIB), can be oriented in one direction to maximize elasticity differences between the parallel and perpendicular directions, minimizing shrinkage.
By reducing the Poisson's ratio to 0.07 or less (compared to 0.4 to 0.5 for conventional elastomers), the researchers significantly reduced screen distortion, even in the stretching direction. This design allowed for virtually no shrinkage perpendicular to the substrate.
The second key approach was using a shear-rolling technique to align the nanostructures on the substrate. This method applies consistent shear force at high temperatures by utilizing a speed differential between rollers and stages.
This technique maintained transparency while enabling consistent alignment of nanostructures on thick substrates. Even when the substrate was stretched by more than 50 %, the researchers observed minimal longitudinal shrinkage.
When applied to an actual device, the researchers found that the traditional elastomeric substrate displayed pixel distortion after 50 % stretching, with vertical pixels either stuck or spaced unevenly. In contrast, the nanostructure-aligned substrate maintained a uniform pixel arrangement, producing a seamless image and clear, undistorted transparency.
This new stretchable substrate is expected to be crucial for industries like solar cells, wearable electronics, and next-generation displays. Additionally, the shear-rolling technique used in this study can be applied to other block copolymers and polymer films, making it a versatile technology for processing large areas.
This research proposes a new method to develop a distortion-free and completely transparent stretchable substrate by precisely controlling the nanostructure, and the shear-rolling process to implement it can be easily applied to mass production and industrialization. We are currently conducting research to realize a real display device with no distortion even when tensile by transferring display light-emitting devices using this substrate.
Dr. Jeong Gon Son, Korea Institute of Science and Technology
Journal Reference:
Hur, J., et al. (2024) Fully Transparent and Distortion‐Free Monotonically Stretchable Substrate by Nanostructure Alignment. Advanced Materials. doi.org/10.1002/adma.202414794.