【Popular Science Tips on Polymers and Materials】--007 When hot water is poured into a mineral water bottle, it turns white + jlszhoujidai

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This post was last edited by ljtjbx on 2015-11-9 08:05. Mineral water bottles are often used in daily life; sometimes hot water is poured into them, and then a strange phenomenon occurs – the transparent mineral water bottle quickly turns white. Why is that? To determine whether a material is transparent, it is necessary to check whether it contains substances that cause diffraction, reflection, and absorption of light. Materials with a more regular crystal structure tend to exhibit reflection and scattering, preventing light from passing through; the lower the degree of crystallinity, the more transparent the material. Amorphous materials such as glass are typical examples of amorphous substances, allowing light to pass through easily, resulting in high transparency. Mineral water bottles are made of polyethylene terephthalate, which is a polymer material that crystallizes easily. When manufacturing these bottles, they are formed by blow molding at high temperatures, and then an annealing process is carried out to eliminate the crystalline regions, thereby enabling optical transparency. When hot water is added to a mineral water bottle, the polyethylene terephthalate molecules undergo reorientation at high temperatures, resulting in the formation of new crystalline regions and thus a loss of transparency.