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The Fantastic Journey of Supercold Liquids: How Does Glass Form at Extremely Low Temperatures?
In the field of material science, the glass transition is a fascinating process with profound scientific significance and applied practicality. When a liquid is cooled or compressed, if its molecular structure cannot crystallize quickly, it forms a glassy solid. This phenomenon is called the glass transition, and its technical term is "glass-liquid transition". Whether it’s a glass bottle or window glass, the essence of these everyday objects comes from this mysterious process.
Glass is more than just a substance; it is a trapped fluid that represents the stability and dynamics of matter in an ultracold state.
The formation of glass often involves structural changes in matter. As a liquid cools, its viscosity increases dramatically, even to the point where it can arithmetically increase by 18 orders of magnitude. This property allows glass to remain in a stable solid form at relatively low temperatures. When the molecules of a liquid cannot arrange themselves in an orderly manner like a crystal, a "cooled" glass form. Glass is therefore an amorphous solid that undergoes no true phase change during its production.
Of course, the process here is not simple. The glass transition process is a dynamic phenomenon, not just a solidification of matter. As the temperature decreases, the internal degrees of freedom gradually lose balance. This means that the movement of the molecules is gradually restricted, eventually forming a solid that is strong and cannot flow. But that doesn't mean they eliminate dynamics; over time, these structures will rearrange themselves to some extent.
As the glass cools, even its structure changes over time, eventually settling into a more stable equilibrium state.
In essence, the formation of glass is a multifaceted process. From tiny changes in chemical structure to macroscopic changes in physical properties, all of these together constitute a complex production process. For example, below the glass transition temperature, the thermal expansion coefficient of a material is close to that of a corresponding crystal. If the cooling rate is slowed down, the relaxation time of the structure can be increased, thereby achieving a higher density glass structure.
It's all about "glass-forming ability," which refers to a material's ability to form glass during a brief cooling process. Different materials have different glass-forming abilities, and accordingly, the composition of these substances will greatly affect the final glass quality. This phenomenon is more common for polymers and other amorphous materials, which tend to form glasses during slow or fast cooling.
Glass is formed not only by rapid cooling, but also by the continuous change of the material's properties, such as color and transparency.
Changes in the microstructure are also an important part of the glass transition process. When a material cools to its glass transition temperature (Tg), the properties of the substance change dramatically. At this time, the glass is no longer a solid in the traditional sense, but is in a special dynamic equilibrium. As time goes by and the environment changes, the structure of the glass may gradually approach a theoretical equilibrium state - a stable crystalline state. People often ask, does this indicate that there is also a hidden phase change in glass at the microscopic level?
However, the nature of the glass transition phenomenon remains controversial. Scientists are continuing to explore whether there are deeper physical mechanisms underlying the glass formation process. Some models suggest that as the temperature of a liquid approaches a certain theoretical value, the arrangement of its internal structure prevents the glass from becoming completely stable. This view has led to a rethinking of the nature of glass: Can we understand or verify through experiments other phase changes of glass or even liquid?
Research is now emphasizing the thermal history of these glasses, that is, the temperature changes they experienced during their formation and their effects. These studies not only help explain the physical properties of glass, but also provide new perspectives on the industrial applications of glass. For example, cooling rates and composition variations during the manufacturing process will significantly affect the quality of the final product.
A variety of techniques allow scientists to determine the transition temperature of glass, which is particularly important in the study of polymers and inorganic glasses. This gives us sufficient basis when designing and applying various glass materials, allowing us to utilize the characteristics of the materials more effectively.
Through these in-depth studies, we can begin to understand how glass-based materials impact the environment around us and their potential benefits across a wide range of technological fields. However, all these discussions are not the end, but a new beginning for the understanding of the properties of matter. What we need to think about is what kind of breakthroughs future scientific research will bring us to unravel the mystery of glass?
