Possibility of developing new materials leading to the realization of “I wish I could” ideas

Lightweight, high-strength carbon nanotube carrying the dream of realizing space elevators

The development of new materials could have a major impact on society. Carbon nanotubes, which you may have heard a lot about, are indeed among such new materials.

They are sheets of carbon atoms connected in mesh-like patterns that have been formed into tubes. As a molecule in itself, the bonds between the atoms are very strong and extremely light. It is also characterized by high electrical conductivity and thermal conductivity.

For example, by mixing a small amount of paint-like coating material with short carbon nanotubes so as not to change their color, the painted material becomes conductive. Some carbon nanotubes have already been used as adulterants to change the properties of materials. However, the problem is that the fibers currently available for manufacturing are too short in length to be used as materials for structures such as machines and airplanes.

The longer the fiber, the much stronger it becomes. To make the fiber longer, however, it takes more time to grow the crystal, and the bigger it becomes, the slower it grows. In my own research, it was found that carbon nanotubes grow straighter and stronger if a tensile force is applied during growth. However, there is still a problem in growing a long single crystal.

If we can synthesize very long fibers without defects in their molecular structure, we may be able to realize a space elevator that connects Earth and space. However, space elevators are structures as high as about eight times the diameter of the Earth. Using a method such as joining short carbon nanotubes together, the desired strength will not be achieved.

Most scientists probably think it’s impossible, but some researchers are working on it, and some companies are starting their own independent research. When it comes to implementation, it will be a global-scale project. As long as there are people doing research on it, it can be hoped that we will see the outcome someday.

Smart materials are materials that respond in some way to external stimuli

Currently, I focus on the development of smart materials. Smart materials are materials that can respond in some way to external stimuli. The term collectively refers to materials that change color or shape when they are subjected to various stimuli such as heat, light, electromagnetic waves, and vibration.

For example, shape memory polymer, which has the characteristics of both rubber and plastic, is one such material. Its molecules do not break like rubber, but deform, and when heat or other stimulus is applied, the molecules become easier to move and return to their original shape.

Also, famous ceramics developed in Japan are those capable of healing cracks, scratches, and other defects by themselves. A substance that acts as a healing agent is applied to the base material, and when a crack occurs, it reacts to heal the damage. It is said that this type of ceramics are being developed for use in aircraft engines and other applications, and designed to heal damages when they touch air at high temperature and cause an oxidation reaction. There seems to be considerable progress in the research to speed up their healing speed.

What is called bimetal, a combination of different metals in film form, has been used for a long time. When the temperature changes, the difference in the heat expansion coefficient between these metals causes them to bend slightly, and they have been used in temperature sensors for decades.

Moreover, research to develop molecular materials themselves is also ongoing. Some molecules change their shape when exposed to light. For example, research has already been done to create molecules that bend when exposed to ultraviolet light and return to their original shape when exposed to ordinary light.

As described above, for such development, in addition to an approach that is to create materials themselves, it is also possible to combine existing materials. Smart materials cover a wide range of fields, and currently, various research activities are diligently carried out in varied places.

Aiming to develop new materials that can move with energy supplied by non-contact stimulation

In our laboratory, we are focusing on the development of smart materials that can be moved by non-contact stimuli such as sound waves and light.

For example, we are developing a material by bonding a metal film and a rubber film under special conditions so that it can be moved by light. While ordinary materials have thermal expansion, rubber causes thermal contraction under certain conditions. By taking advantage of these conditions, we are accumulating improvements to make it can be moved a lot more.

The basic idea is the same as bimetal, but the bimetal only moves extremely slightly. Rubber used here is not just ordinary rubber, but a mechanism that efficiently converts light into heat is imported into it, and various additives are incorporated into the raw material. For combining the two films, we performed mechanical calculations to determine the ideal thickness and calculated the conditions under which the rubber would shrink by heat. As a result, in the past few years, we have seen results of movement that have increased by several hundred times.

The material can also be moved from a distance by using laser light. How and where to use it depends on future considerations, but as development progresses and more people get to know about it, we’ll be able to see new ways to use it that were never thought of before.

We are also developing a material that operates with sound waves. In this case, we did not modify the material itself, but the structure of the material is modified. For example, we use a periodic structure like a hexagonal honeycomb and connect many of them to form a single material, which can be treated as a metamaterial that moves with sound waves or ultrasonic waves.

If it is developed well, we consider, for example, it could be applied to drug delivery in the future. If we can open the capsule of a drug in the body at the target site using ultrasonic waves, we can maximize the effect of the drug and minimize the side effects.

Even if it’s not inside the body, it could be used in places where electricity cannot be directly applied or where tools cannot be directly placed, such as pipes and pressure vessels. We hope that this will lead to technologies that encourage things to do work by providing external stimulation.

As the term “smart materials” has become more widely used, more and more people are studying them, and their development seems to be more active. There aren’t many examples of this yet, but they will be useful in the future. It is an exciting dream to develop new materials that exhibit new functionality by combining various physical phenomena. We will continue our research so that we can bridge the seeds created here to the industrial sector and lead to practical applications.

* The information contained herein is current as of October 2024.
* The contents of articles on Meiji.net are based on the personal ideas and opinions of the author and do not indicate the official opinion of Meiji University.
* I work to achieve SDGs related to the educational and research themes that I am currently engaged in.

Information noted in the articles and videos, such as positions and affiliations, are current at the time of production.