题型:阅读理解 题类:常考题 难易度:普通
广东名校联盟(广州二中、珠海一中、中山纪中)2019-2020学年高二上学期英语期中联考试卷
Scientists have created a scent(气味)-delivery system that releases a pleasant fragrance when you sweat. Apply it to your skin, and the more you sweat, the better you'll smell. That's because the perfume only gets released upon contact with moisture(湿气).
Chemists from Harvard University combined two compounds to create their new system. One chemical is alcohol-based. This is the nice-smelling perfume. The other chemical is an ionic liquid(离子性液体), which is a type of salt that is liquid at room temperature. Ionic liquids are made of ions—molecules(分子) that have lost or gained one or more electrons(电子). If the molecule loses electrons, it will have a positive charge(正电荷). If it gains electrons, it gets a negative charge. Ionic liquids contain the same number of positive and negative ions, which makes them neutral, with no overall electric charge. In general, ionic liquids have no smell.
When the perfume and ionic liquid are mixed together, a chemical reaction occurs. This bonds the molecules to each other. The reaction also temporarily inactivates the perfume's molecules. So when applied to the skin, the new perfume has no scent in the beginning. But adding water or sweat breaks the bond between the molecules. That releases the scent into the air.
"The rate of the release of the fragrance depends on how much you sweat, in other words, how much water is available," explains chemist Nimal Gunaratne from Harvard University, who led the research. "Sweat is like the command to let the fragrance go."
Christian Quellet is a chemist who has worked in the perfume industry for a long time. He is now an independent consultant based in Switzerland. "Gunaratne's perfume opens the door to new developments and applications of fragrance controlled-release systems," he says. Controlled-release systems allow small quantities of some compounds that they hold to enter the environment slowly.
The system also traps some chemicals in sweat that are responsible for the bad sweat smell. These compounds are called thiols (硫醇). Just as water does, thiols break apart the bond that ties the perfume to the ionic liquid. When this happens, the thiols attach to the ionic liquid and their bad scent is inactivated as the perfume had been. This means the water in sweat and its thiols are both able to release the fragrance from the newly developed perfume.
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