Supercritical fluids represent a fascinating state of matter that transcends the traditional distinctions between solid, liquid, and gas. In the realm of stable pure substances, we commonly encounter solid, liquid, gas, glassy, and rubbery states. However, there exists a critical state, a boundary where gas and liquid coexist seamlessly, leading to the disappearance of the interface between the two phases.
This critical state is achieved by navigating along the curve of gas-liquid coexistence on a typical phase diagram, moving towards higher temperatures and pressures. As this journey progresses, the substance eventually reaches its critical point-marked by a critical temperature and critical pressure. At this juncture, an intriguing transformation occurs. The density of the liquid phase matches that of its saturated vapor, completely erasing the boundary that separates the gas and liquid phases. The substance transitions into what is known as a supercritical fluid.
This transformation at the critical point is driven by the interplay of temperature and pressure. Rising temperatures induce thermal expansion, reducing the density of the liquid phase, while increasing pressure compresses the gas phase, rendering it denser. The critical point represents the equilibrium where these opposing effects culminate. Beyond this critical temperature, the substance defies the conventional process of condensation and evaporation. Instead, it takes on the form of a supercritical fluid, existing in a flowing state within the critical zone.
In the supercritical fluid state, the gaseous substance mirrors the density of a liquid under normal conditions. Intriguingly, as pressure rises, these supercritical fluids exhibit a remarkable increase in dissolution ability. This unique behavior opens up a realm of applications, from extraction processes to advanced materials, where the distinctive properties of supercritical fluids find practical and innovative uses. Thus, the study and understanding of supercritical fluids offer a gateway to unlocking novel possibilities and pushing the boundaries of conventional states of matter.