Mechanical Stress Leads to Self-Sensing in Solid Polymers
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beams. They also found that control of the intensity of the optical beams was critical to observing transistor-like action in the single molecule. Sandoghdar said, “Many more years of
research will still be needed before photons replace electrons in transistors. In the meantime, scientists will learn to manipulate and control quantum systems in a targeted way, moving them closer to
the dream of a quantum computer.” Thus component parts such as the new single molecule optical transistor may also pave the way for a quantum computer.
Mechanical Stress Leads to SelfSensing in Solid Polymers
Now, as reported in the May 7 issue of Nature (DOI: 10.1038/nature07970; p. 68), the researchers show they can perform a similar feat in a solid polymer. The researchers used molecules called spiropyrans, a class of molecular probes that serve as color-generating mechanophores, capable of vivid color changes when they undergo mechanochemical change. Normally colorless, the spiropyran used in the experiments turns red or purple when exposed to certain levels of mechanical stress. “Mechanical stress induces a ringopening reaction of the spiropyran that changes the color of the material,” said D. Davis, a graduate research assistant and the article’s lead author. “The reaction is reversible, so we can repeat the opening and closing of the mechanophore.” To demonstrate the mechanochemical response, the researchers prepared two different mechanophore-linked polymers and subjected them to different levels of mechanical stress. In one polymer, an elastomeric mechanophore-linked poly(methyl
acrylate) (PMA), the material was stretched until it broke in two. A vivid color change in the polymer occurred just before it snapped. The second polymer, a glassy mechanophore cross-linked poly(methyl methacrylate) (PMMA), was formed into rigid beads 100–500 μm in diameter. When the beads were squeezed, they changed from colorless to purple. The color change that took place within both polymers could serve as a good indicator of how much stress a mechanical part or structural component made of the material had undergone. “We’ve moved very seamlessly from chemistry to materials, and from materials we are now moving into engineering applications,” Sottos said. “With a deeper understanding of mechanophore design rules and efficient chemical response pathways, we envision new classes of dynamically responsive polymers that locally remodel, reorganize or even regenerate via mechanical regulation.”
and physics at Yale. “But this is the first time it has been done in an all-electronic device, which looks and feels much more like a regular microprocessor.” As reported in the June 28 online issue of Nature (DOI: 10.1038/nature08121), the research team used artificial atoms as quantum bits, or qubits. Although made from over a billion aluminum atoms in a superconducting electronic circuit, these qubits behave as single atoms. The difference is that the manufactured atoms are much larger and therefore easier to control than single atoms or other types of qu
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