|
Seeing Red Means Danger Ahead The color red often means danger-and by paying attention，accidents can be prevented．In the future，the color red also may help{{U}} (51) {{/U}}danger at construction sites．Thanks to new work by engineers，bridge supports-or{{U}} (52) {{/U}}kinds of materials-could one day contain a color-changing material．It will turn red{{U}} (53) {{/U}}a structure collapses or falls apart． The secret{{U}} (54) {{/U}}the color-changing material is a particular type of molecule(分子)．A molecule is a group of atoms(原子)held together by chemical bonds．Molecules come{{U}} (55) {{/U}}all shapes and sizes，and make up{{U}} (56) {{/U}}you can see，touch or feel．How a molecule behaves depends on {{U}}(57) {{/U}}kinds of atoms it contains，and how they're held together． When a polymer(聚合物)containing a color-changing molecule called a mechanophore(机械响应性聚合物)is about to break，it produces a{{U}} (58) {{/U}}．When a polymer with mechanophore molecules becomes“injured”or{{U}} (59) {{/U}}，one of the mechanophore bonds{{U}} (60) {{/U}}and the material turns red．“It's a really simple detection method，”says Nancy Sottos，one of the scientists who worked on the project．Sottos and her team tested the color-changing polymers in their lab．The test{{U}} (61) {{/U}} proved encouraging． There is a way to get rid of the red color：light．When a bright light is shone on the mechanophore， the broken bond is fixed-and the red color{{U}} (62) {{/U}}．This“self-healing”may be a problem for engineers．They need to use the color-changer in big construction projects that will be{{U}} (63){{/U}}，in sunlight．And sunlight will make the mechanophore's warning system{{U}} (64) {{/U}}． Sottos and her fellow scientists still have{{U}} (65) {{/U}}work to do before the color-changing molecules can be used outside the lab． |