Molecular origin of the shape memory properties of heat-shrink crosslinked polymers as revealed by solid-state NMR

Fabrication of Hierarchical Microstructures via Laser-Induced Shrinkage of Shape Memory Polymers for Flexible Pressure Sensing

Hierarchical microstructures are widely recognized as one of the most effective components for enhancing the performance of flexible pressure sensors. However, the rapid and controllable fabrication of pressure sensing layers with hierarchical microstructures remains a significant challenge. In this study, we propose a method that utilizes laser-induced microscale shrinkage of shape memory polymers to enable rapid and controllable fabrication of hierarchical microstructures for high-performance pressure sensing. We systematically investigate the influence of UV laser fabrication parameters on the architecture and morphology of hierarchical microstructures. A flexible pressure sensor, equipped with optimized hierarchical microstructures, exhibits a high sensitivity larger than 15 kPa-1 and excellent linearity (R2 = 0.994) in a range from 0 to 200 kPa. It features response and recovery times of 57 and 62 ms, respectively, and maintains good stability, enduring over 5,000 cycles. The laser-induced shrinkage of shape memory polymers offers an effective method for the fabrication of hierarchical microstructures, holding great potential to boost the performance of flexible pressure sensors in applications within intelligent robotics and wearable healthcare.

Progress of shrink polymer micro- and nanomanufacturing

Traditional lithography plays a significant role in the fabrication of micro- and nanostructures. Nevertheless, the fabrication process still suffers from the limitations of manufacturing devices with a high aspect ratio or three-dimensional structure. Recent findings have revealed that shrink polymers attain a certain potential in micro- and nanostructure manufacturing. This technique, denoted as heat-induced shrink lithography, exhibits inherent merits, including an improved fabrication resolution by shrinking, controllable shrinkage behavior, and surface wrinkles, and an efficient fabrication process. These merits unfold new avenues, compensating for the shortcomings of traditional technologies. Manufacturing using shrink polymers is investigated in regard to its mechanism and applications. This review classifies typical applications of shrink polymers in micro- and nanostructures into the size-contraction feature and surface wrinkles. Additionally, corresponding shrinkage mechanisms and models for shrinkage, and wrinkle parameter control are examined. Regarding the size-contraction feature, this paper summarizes the progress on high-aspect-ratio devices, microchannels, self-folding structures, optical antenna arrays, and nanowires. Regarding surface wrinkles, this paper evaluates the development of wearable sensors, electrochemical sensors, energy-conversion technology, cell-alignment structures, and antibacterial surfaces. Finally, the limitations and prospects of shrink lithography are analyzed.

Rigid High Temperature Heat-Shrinkable Polyimide Tubes with Functionality as Reducer Couplings

Flexible and semi-rigid heat-shrinkable tubes (HSTs) have been used in thousands of applications, and here rigid high temperature HSTs are reported for the first time. These rigid HSTs are prepared with shape memory polyimides possessing glass transition temperatures (Tgs) from 182 to 295 °C, and the relationships between Tg and their molecular structures are studied. The polyimide HSTs (PIHSTs) can fix expanded diameters and shrink back to original diameters very well, and the mechanisms of their heat-shrinkage performance are discussed. Their differences from commercially available HSTs in heat-shrinkage are also analyzed. They can withstand low temperature of -196 °C, much lower than those of other HSTs. The PIHSTs can also connect subjects of different sizes by heat-shrinkage and then fix them upon cooling like reducer couplings, and the possible mechanisms of their reducer coupling effect are analyzed. With their unique characteristics, PIHSTs will expand the application areas of HSTs enormously.