In this blog post, we will look at the impact of singularities and the scientific principles of supercritical fluids, which are turning points in technological advancement, on our daily lives and industries.
“The Singularity is Coming!” This is what many people who watched the shocking Go match between Google’s AlphaGo and Lee Sedol 9th Dan shouted on the Internet. This expression became famous after being used as the title of a book written by Ray Kurzweil, Google’s director of engineering, who describes the point at which technology created by humans transcends humans as the singularity. In other words, the author argues that the singularity is the point at which human technology and human capabilities become the same, and that once we cross this singularity, things will happen that we never expected. The unexpected things here also refer to a future in which artificial intelligence will learn and evolve independently, surpassing our human expectations and thinking and making decisions like humans.
However, the word singularity is often used in mathematics and science as a broad concept that refers to a point at which competing things are in balance with each other, in addition to the balance between technology and humans. For example, in mathematics, the characteristics of a formula are sometimes determined by the ratio of two variables in the formula. However, the sizes of the two factors are so perfectly balanced that it is impossible to say anything about the characteristics of the equation, which is called a singular point of the equation. If we understand the word “singular point” in this broader sense of “balance point,” we can see that the state of all the substances around us also has a singular point unique to each substance, which is called a critical point, when the characteristics of liquid and gas are balanced. And when it crosses this threshold, it shows useful properties that we never imagined.
All matter can exist in three states. Take water as an example. When the temperature is low, it exists as a solid state called ice. When the temperature rises, it melts and becomes a liquid called water. When it gets even hotter, it boils and becomes a gas called water vapor. As such, the three states of matter—solid, liquid, and gas—change depending on temperature. In addition, the state of matter changes not only with temperature but also with pressure. The spray in the can is compressed at very high pressure and is in a liquid state, but when it is sprayed, it becomes an invisible gas and is blown out into the air. As such, the state of matter, whether solid, liquid, or gas, is determined by temperature and pressure. This is a common phenomenon around us, but it is even more interesting to note that each state can only be maintained at a specific temperature and pressure. The process of water, which is in a solid state, melting into a liquid and then becoming a gas again, is something we can easily witness in our daily lives, but behind it lies a complex interaction between molecules.
So how do temperature and pressure change the state? First, let’s look at what temperature and pressure mean. Temperature indicates how fast the molecules, the tiny particles that make up a substance, move. In other words, when the temperature is low, the molecules move slowly, and when the temperature rises, the molecules move quickly. On the other hand, pressure indicates the distance between molecules. High pressure means that the material is compressed and the distance between molecules is small, and when the pressure is lowered, the distance between molecules becomes larger. However, this adjustment of the distance between molecules by pressure has an additional effect. Molecules have a tendency to pull each other, and the magnitude of the pulling force increases when the molecules are closer together. In other words, when the pressure increases, the molecules get closer together, increasing the force of attraction and cohesion between them. Conversely, when the pressure decreases, the force of attraction between the molecules weakens.
Now let’s go back to water. When the temperature is low, the water molecules that make up water move slowly. These slowly moving molecules overcome the forces of attraction and cannot escape, so they become stuck together and form a solid state, or ice. When the temperature of the ice rises to a certain level, the molecules begin to move more quickly. Although the molecules are still stuck together in large clumps, they are able to move around a little bit due to the force of attraction between them. This is liquid water. If the temperature is further increased, the force of attraction between molecules becomes so fast that they can no longer hold each other together and the molecules become free to fly around, which is the state of gas-phase water vapor. In short, the state of matter is determined by which force, the force of attraction between molecules or the force of friction, is stronger, and the state of matter changes depending on temperature and pressure because the force of attraction between molecules increases with pressure and the speed of molecules increases with temperature.
Then, let’s try to turn water vapor into liquid without lowering the temperature. When the pressure is increased, the water molecules get closer to each other. And the force of attraction between the molecules also increases. When the pressure is increased to a certain level, the force of attraction between the molecules becomes so strong that they can even catch the molecules that are running away at a high speed, and they will turn back into liquid. But can we always turn gas into liquid by increasing the pressure?
To answer the question in advance, the answer is no. Increasing the pressure reduces the distance between molecules and increases the force of attraction between them. However, there is a limit to how much pressure can be applied. This is because molecules will not get any closer to each other until they are compressed so tightly that there is no space between them. On the other hand, the temperature can be raised indefinitely until a problem occurs inside the molecules or they decompose. Therefore, when a certain temperature is exceeded, the competition between pressure and temperature ends, and no matter how much pressure is applied, the molecules cannot create a strong enough force to pull each other together to catch the fast-moving molecules, and the gas does not turn into a liquid. The last point of equilibrium, just before the competition between temperature and pressure breaks down, is called the critical point, which can be seen as the singularity of matter.
However, the fact that a substance cannot become a liquid once the temperature and pressure of the critical point are exceeded does not mean that the substance beyond the critical point exists as a gas. Once the critical point is exceeded, the distance between molecules is so close that they are pulled together by strong forces, although not to the extent that they become a liquid. Therefore, even though the molecules are not as tightly packed as when they are liquid, they cannot move around as freely as when they are gas. A substance that has crossed the critical point and is neither liquid nor gas is called a supercritical fluid.
Supercritical fluids exhibit properties that are not seen in ordinary liquids or gases, including very low viscosity and the ability to dissolve other substances very well. Low viscosity means good penetration, which can be easily understood by comparing it to water and honey. When water is poured into sand, it can penetrate into every corner of the grains and flow out, but when honey, which has a higher viscosity than water, is poured into sand, it hardly flows and only seeps into the sand a little.
In short, when supercritical fluid is used as an extraction solvent, it can penetrate every corner and dissolve other desired substances. When sesame seeds are pressed to extract sesame oil, the amount of lignin, an antioxidant that does not melt, can be increased by more than 10,000 times by using supercritical fluid, and sesame oil extracted in this way is actually sold on the market. In addition, supercritical fluids can be used to selectively remove caffeine from coffee during the decaffeination process. Many pharmaceutical companies are also conducting research to use supercritical fluids to extract active ingredients from herbs and other substances. Supercritical fluids are also being actively used to produce nanoparticles and as a medium to induce advanced chemical reactions. As such, supercritical fluids are becoming a key material for advanced technologies, and their applications are expanding.
