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HOME > No.2, Sep 2015 > Feature Story : Free Architectural Design and synthesis of Nanocomposites

Free Architectural Design and Synthesis of Nanocomposites

Hiroyuki Muto

Hiroyuki Muto and one of his students
Hiroyuki Muto and one of his students

In recent years, nano-sized materials have been attracting tremendous attention in many research fields such as structural materials, cosmetics and medicine. The reason for this is that the unique physical properties of nanomaterials, such as quantum, surface and interface effects, facilitate the development of many new applications for these materials. Until now however, nanomaterials’ complexity hindered their effective utilization; resulting in little progress in their practical applications. Nevertheless, Dr. Hiroyuki Muto, professor of Institute of Liberal Arts & Science and Department of Electrical and Electronic Information Engineering (acting), had developed a simple but novel method that enables the synthesis of uniform nano-sized composite materials utilizing electrostatic interactions. Currently, Dr. Muto is advancing his research towards the mass production of nanomaterials.

Interview and report by Madoka Tainaka

The key is “electrostatic interaction”

“I think many of you know very well what a carbon nanotube is. However, if I ask you about the practical applications of a carbon nanotube, I doubt many of you would be able to answer my question, which would be fair enough, as few practical applications currently exist.

A carbon nanotube is a thread-like material that can conduct electricity and upon mixing with translucent materials, it can be utilized in many applications such as touch panels and solar panels. However, during preparation, carbon nanotubes tend to shrink into a ball of thread or harden upon mixing. Moreover, as it is difficult to obtain a uniform mixture of carbon nanotubes, a large amount is usually required during the mixing process. As carbon nanotubes are very expensive, it is not therefore easy to practically fulfill their immense theoretical potential.,” explains Dr. Muto.

In the conventional fabrication of composite materials, the required raw materials are mechanically stirred in a container with sticks or hard balls, which is also known as ‘mixing’. In reality, it is actually very difficult to obtain a very well balanced and distributed mixture. Despite the adoption of various measures to improvise the mixing process such as chemical additives and controlling the level of force and time during mixing, crucial issues such as structural decomposition resulting from the impact of mixing remained unresolved. Therefore, it is almost impossible to synthesize minute/fine composites by just mixing the materials.

Photo of the system
Adhered nano-sized materials around a micro particle

“When materials with different specific gravities are mixed, they tend to separate and resist uniform mixing. It is also a challenge to mix the proper amount of conductive materials (as mentioned previously for carbon nanotubes) and at the same time align them in a continuous arrangement. Therefore, we came up with the idea of synthesizing a composite material by adhering nano-sized materials around a micro particle that is used as the parent material (matrix).”

The principle of adhering the nano-sized materials onto the matrix particle is based on “electrostatic interaction.” Electrostatic interaction is the force that acts between positive and negative charges. Dr. Muto has succeeded in using this well-known physical phenomenon to construct composite materials in a simple manner.

Synthesizing a wide variety of composite materials by freely controlling the surface electric charges of a particle

This method for synthesizing a composite material is very simple and easy to understand.

Concept of development for novel nanocomposite via composite particle
Concept of development for novel nanocomposite via composite particle

“First, the electric charges on the surface of the matrix particle and the nanomaterial (which is the additive) are controlled to be either positive or negative, in order to generate opposite polarities. Then, both materials are added into a solution such as water and stirred in such a way that the nanomaterial is successfully absorbed onto the surface of the matrix particle. The preparation procedure involves the addition of the materials into a polyelectrolyte solution (a material that produces polymer ions upon dissolution in water, such as the positively charged poly diallyldimethylammonium chloride or the negatively charged sodium polystyrenesulfonate) so that the surface of each material has either a positive or negative charge. This method enables quick room-temperature synthesis of composites, without being affected by the specific gravity difference of the constituent materials. Moreover, the amount of nanomaterials absorption can be freely regulated”, Dr. Muto explains.

Firstly, all materials have their own specific electric charge. For example, if silica (silicon oxide) is added into neutral water, it would become negatively charged. However, this does not always occur, and in some circumstances, the electric charge may be too weak and cannot be used as it is. However, Dr. Muto explains that if a polyelectrolyte is used, it is possible to charge the material uniformly with a strong electric charge. In addition, the alteration of electric charge between positive and negative is possible regardless of the original surface electric charge of the particle. By adopting this method, it is feasible to synthesize composites with various functionalities depending on the combinations of matrix particles and nanomaterials that are absorbed.

“Actually, this method is based on electrostatic interaction, which is already used in the synthesis of functional “nano” thin films (two-dimensional structures). So although the method is not new, we succeeded in using it for the first time to synthesize integrated three-dimensional architectural nanocomposites that consisted of particles of various sizes. When the composite is dried, it is applicable as a powder. By increasing the concentration, it can be utilized as a paste. In powder metallurgy, the composites can also be pressed, formed, and hardened thermally into a block. One of the highlights of this method is the ability to synthesize and design the dimension or form of the nanomaterials in order to utilize their properties in accordance to the specific requirements”, Dr. Muto proudly explains.

The composite particles synthesized in this way are bound strongly, which makes the material stable and more energy efficient compared to those synthesized by mechanical mixing. This method was not originally suitable for materials that did not possess wettability, water solubility or buoyancy because this process involves dissolution into a solvent. However, through the application of many creative ideas, it has become applicable for almost all materials at this point.

As an example, Dr. Muto worked on the development of a conductive material using carbon nanotubes. In this project, Dr. Muto succeeded in synthesizing a material that has high transparency, while greatly reducing the amount of carbon nanotubes used.

Working on the development of a manufacturing process towards mass production

Owing to the superiority of this research, it was adopted as one of the Industrial Technology Research Grant Programs of the New Energy and Industrial Technology Development Organization (NEDO) from 2009 to 2012. From 2015, the research has advanced further into the Innovative Design and Production Technology project in the Cross-ministerial Strategic Innovation Promotion Program (SIP) of the Cabinet Office. Currently, Dr. Muto is working on the process development that enables mass production of composite nanomaterials (composite particles). Moreover, industries in various fields are expressing their interest in this technology.

In relation to his goal, Dr. Muto said, “Material study does not immediately come across as a glamorous field of study, but in fact it has great influence on society. For example, just by changing the composition of a material, its strength can be doubled or reduced to half. It is therefore challenging. The production rate varies for different materials, but in the near future, I hope to be able to produce about 10 kg of composite particles per hour.” It is very exciting to see what kind of novel materials will be synthesized with this method developed by Dr. Muto.

This study was supported by Cross-Ministerial Strategic Innovation Promotion Program (SIP) of Council for Science, Technology and Innovation (CSTI), Japan.

Dr. Muto and his research colleagues were awarded the “Editor-in-Chief's Featured Article” by the Journal of Supercritical Fluids (Elsevier)

The Journal of Supercritical Fluids “Editor-in-Chief's Featured Article” August 2015

This is an award given to the top three papers chosen from all published articles in 2014 by the editorial committee of the Journal of Supercritical Fluids.

Awarded to

Kiyoshi Matuyana, Yu-ki Maeda, Takaaki Matsuda, Tetsuya Okuyama (National Institute of Technology, Kurume College) . Hiroyuki Muto (Toyohashi University of Technology)

Title of awarded article

Formation of poly (methyl methacrylate)-ZnO nanoparticle quantum dot composites by dispersion polymerization in supercritical CO2.

By TUT Research editor

Reporter's Note

Toyohashi University of Technology has many members who graduated from a technical college, as the university promotes collaborations with other technical colleges. Dr. Muto himself has also graduated from the National Institute of Technology, Fukushima College.

“People from technical colleges are accustomed to experiments, and many of them enjoy the process. Therefore, they share the tendency of trying out their ideas hands-on. This research started in the same way too, where I tried my idea in an experiment and surprisingly, the result was better than expected.” Dr. Muto laughed.

Dr. Muto was originally working on research regarding the fracture mechanics of materials. He chanced upon his current research when he first started to synthesize his own ceramics for evaluation purposes. It’s safe to say that Dr. Muto’s significant research results are the fruit of his dedicated attitude toward experiments.


  • Matsuyama, K., Maeda, Y., Matsuda, T., Okuyama, T., and Muto, H. (2015). Formation of Poly(Methyl Methacrylate)-ZnO Nanoparticle Quantum Dot Composites by Dispersion Polymerization in Supercritical CO2, The Journal of Supercritical Fluids, 103, 83-89.
  • Phuc, N. H. H., Okuno, T., Hakiri, N., Kawamura, G., Matsuda, A., and Muto, H. (2014). Synthesis of High-Edge Exposure MoS2 Nano Flakes, Journal of Nanoparticle Research, 16(1), 2199.
  • Tan, W. K., Razak, K. A., Lockman, Z., Kawamura, G., Muto, H., and Matsuda, A. (2014). Synthesis of ZnO Nanorod-Nanosheet Composite via Facile Hydrothermal Method and their Photocatalytic Activities under Visible-Light Irradiation, Journal of Solid State Chemistry, 211, 146-153.
  • Phuc, N. H. H., Okuno, T., Matsuda, A., and Muto, H. (2014). Ex Situ Raman Mapping Study of Mechanism of Cordierite Formation from Stoichiometric Oxide Precursors, Journal of the European Ceramic Society, 34(4), 1009-1015.

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Researcher Profile

Dr. Hiroyuki Muto studied at Toyohashi Tech, and received his PhD. in 1997, Japan. Since 1997, Dr. Muto has been involved in researching the deformation and flow mechanism of brittle ceramic materials at elevated temperatures at Toyohashi Tech. He was involved in the development of nanocomposite ceramic materials. He was also a visiting research associate of Professor David Willkinson’s group in the Department of Materials Science and Engineering at McMaster University from 2005 to 2006. Currently, Dr. Muto is a professor in the Institute of Liberal Arts and Sciences at Toyohashi University of Technology, Japan. He has more than 15 years of research experience in materials science, and has published extensively in peer-reviewed journals.

Reporter Profile

Madoka Tainaka is a freelance editor, writer and interpreter. She graduated from the Department of Law, at Chuo University, Japan. She served as a chief editor of “Nature Interface” magazine, and on the committee for the Promotion of Information and Science Technology at MEXT (Ministry of Education, Culture, Sports, Science and Technology).