RESEARCH

1. Light-stimuli responsive liquid crystalline polymers

Soft robots: We are developing multi-stimuli responsive liquid crystalline (LC) polymer–based soft robots that can be actuated thermally, photothermally, photochemically, or magnetically, enabling multifunctional, direction-controlled locomotion such as rolling, crawling, and jumping. The responsiveness is imparted by incorporating UV-sensitive dyes (e.g., azobenzene) and magnetically sensitive particles (e.g., NdFeB, Fe). Owing to the programmed alignment of the LC polymer, their motion can be remotely controlled by tuning the order parameter and internal self-assembled structures, including twisted nematic and super-twisted nematic configurations. These light-driven, reconfigurable soft robots hold great promise for untethered operation and exploration in confined or hazardous environments.

Shape-reconfigurable devices: As a versatile platform for shape reconfiguration, liquid crystalline (LC) polymers are outstanding candidates for next-generation electronics. We have developed LC polymer composite–based devices such as locomotive electronics and shape-reconfigurable supercapacitors. By integrating LC polymers with 2D materials like graphene and MXene, we created highly conductive, mechanically adaptive composites suitable for smart, morphable electronics. Moreover, through the combination of inkjet and multi-layer printing techniques, we fabricated supercapacitors that exhibit programmed shape reconfiguration in response to temperature variations and infrared light–induced photothermal effects.

2. Magnetically responsive polymer composites

Soft robots: Magnetic fields facilitate battery-free remote control of soft robots. We investigate the magnetically-responsive soft robots. Diverse 3D anisotropic magnetic robots are capable of versatile locomotion such as uphill climbing and agile swimming both underwater and above water. Additionally, the autonomous coordination of the magnetic robots facilitated various robotic tasks, including cargo transportation and microfluidic vortex regulation. Recently, magnetic swarm intelligence has been achieved by programming the assembly configurations of robots. The magnetic swarms can execute versatile tasks such as self-throwing over an obstacle, lifting of an obstacle, wire connection and disconnection, liquid metal shape modification, tube unclogging, and organism guiding.

Micropillar arrays: Our research interests include 3D micro-structured surfaces for wetting, adhesion, antireflection, printing, and other diverse applications. Magneto-responsive micropillar arrays provide various reconfigurable surfaces by bringing about instantaneous responses from multiple objects via contactless control. We demonstrate reversible multimodal magneto-actuation of micropillar arrays, enabling stepwise collective magnetic self-assembly, on-demand chirality selection of nature-inspired arrays, and guided worm locomotion. Recently, our team achieved collective and rapid high-amplitude magnetic oscillation of micropillar arrays, as well as nature-inspired complex 3D microfabrication via shape fixation of magnetically deformed microarrays. 

1. Petroleum-derived materials 

Elemental sulfur (S) is a by-product which is generated to a vast surplus of 7 million tons per year in the petroleum refining processes. We can easily synthesize the stable and solid-state sulfur-rich polymer having a sulfur backbone by inverse-vulcanization. The sulfur-rich polymer has unique properties that can be applied to infrared (IR) optics and green energy harvesting. Compared to carbon-based polymers, sulfur-rich polymers show intrinsically high refractive index and transmission of IR region, allowing them to have applications in IR lenses and polarizers. Furthermore, the high electron affinity of elemental sulfur (~200 kJ/mol) enables the sulfur-rich polymer to generate surface charge density facilitating its application in triboelectric nanogenerator (TENG). We fabricated the world’s first sulfur-rich-polymer-based TENG. A sulfur-rich polymer-based composite with the emerging nanomaterial MXene enabled an ultrahigh-performance TENG. The sulfur-rich polymer can also be applied in the field including battery and mercury filtration.

2. Bio-derived materials (cellulose, lignin)

The fabrication of polymer composites has been a prevailing research interest with its straightforward methods, but the fundamental understanding of the properties of polymer composites remains a puzzling and challenging area. Our aim is to fabricate polymer composites with enhanced thermomechanical properties using natural-derived filler materials and to clarify the processing-structure-property relationships. Designed to maximize favorable interactions among the components and following optimization efforts, plain melt mixing strategies can effectively blend conventional polymers with excess wood waste materials, such as cellulose and lignin. Recently, our group was selected to participate in the Global Center for Sustainable Bioproducts (GCSB), an international research initiative. GCSB aims to develop sustainable bio-derived composites and plastics to replace petroleum-based materials. By collaborating with leading experts from the US, Canada, Finland, Japan, Korea, and the UK, we will explore innovative uses of waste biomass for bioplastic production.