Mechanophysical Synthesis of Core/Shell Supraparticles

Abstract

Surface modification of polymer microparticles (MPs) is often essential to impart functionalities beyond their inherent properties. However, decorating these surfaces typically requires complex, multi-step wet chemistry processes to direct assembly and bonding between surfaces, which are not only challenging to control and scale up but also pose significant environmental concerns. Inspired by asteroid impact events, assembly of core/shell hybrid supraparticles (HSPs) is demonstrated via collision-driven, one-step dry mixing of inorganic nanoparticles (NPs) and polymer MPs with a significant contrast in elastic moduli- a process termed "mechanophysical synthesis." Through the interplay of interfacial energy and collision energy, NPs are stably embedded onto the MP surface. The degree of surface coverage depends on mixing velocity and duration, aligning with results from particle collision simulations. HSPs can be created from a diverse combination of MPs and NPs, regardless of their shapes or chemistry. Furthermore, different types of functional NPs-such as magnetic, photocatalytic, and ion-adsorptive-can be simultaneously introduced onto the MPs. The resulting HSPs can not only remove toxic water pollutants, but also be easily recovered and reused. The mechanophysical synthesis approach opens a new direction for sustainable and versatile self-assembly of heterogeneous MPs, minimizing the use of excessive chemicals and solvents.

A collaborative research team, led by Professor Dong Woog Lee from the School of Energy and Chemical Engineering at UNIST, along with Dr. Seunggun Yu from the Insulation Materials Research Center of the Korea Electrotechnology Research Institute (KERI), has developed a novel hybrid supraparticle synthesis technology that enables the attachment of inorganic nanoparticles onto polymer microspheres via simple mechanical collisions.

This innovative approach, which combines functional inorganic nanoparticles with polymer microspheres to form core-shell hybrid supraparticles, holds vast potential across various industries-including energy storage, catalysis, pharmaceuticals and biotech, semiconductor packaging, and insulating materials for power devices. Traditionally, such material bonding has relied on complex, multi-step wet chemical processes, which pose significant challenges, such as increased costs, environmental concerns due to solvent use, and limitations in surface functionalization for bonding heterogeneous materials.

Addressing these issues, the joint research team drew inspiration from the impact craters formed on moons by asteroid collisions. They introduced a collision-based approach that physically and mechanically drives the assembly process. Specifically, inorganic nanoparticles are individually attached onto the surface of polymer microspheres-forming a core-shell structure where the nanoparticle acts as the shell, enveloping the core.

Figure 1. Synthesis of organic-inorganic HSPs through mechanophysical assembly.

While conceptually straightforward, the practical implementation was highly challenging. To ensure stable attachment, the team meticulously optimized various parameters, including particle size ratios, collision velocity and rotational energy, surface energy, and surface roughness. Overcoming these technical hurdles required precise control and fine-tuning of these factors, KERI successfully identified the optimal conditions for attaching inorganic nanoparticles onto microspheres of varying sizes and properties. This achievement represents the first instance of a purely physical adhesion process used to create such diverse hybrid supraparticles, introducing a groundbreaking technique in the field.

The team also performed detailed analyses of nanoparticle coverage, attachment stability, and interfacial durability under thermal, mechanical, and chemical stresses. The resulting hybrid supraparticles demonstrate high multifunctionality-including magnetic, photocatalytic, and adsorption capabilities-and exhibit excellent stability across diverse environmental conditions.

Highlighting the environmental benefits, the researchers note, "Our dry, solvent-free process simplifies the assembly of functional materials, making it highly scalable and environmentally friendly." They further emphasize that "[T]he broad compatibility with various materials, combined with the simplicity and high reproducibility of the process, significantly lowers industry entry barriers."

This research has garnered recognition in the scientific community, featured as the Inside Front Cover in Advanced Materials, a leading journal in materials science with an impact factor of 27.4, placing it among the top 1.9% of publications worldwide. The project was conducted under KERI's core research program, with contributions from Dr. Seung-Yeol Jeon of KIST and Professor Shu Yang of the University of Pennsylvania.

Journal Reference

Jeonguk Hwang, Seong Hwan Lee, Jinsu Kim, et al., "Mechanophysical Synthesis of Core/Shell Hybrid Supraparticles," Adv.Mater., (2025).