POWERING NANOROBOTS
POWERING NANOROBOTS
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DOI：
10.1038/scientificamerican0509-72
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发表时间：
2009-05-01
影响因子：
3
通讯作者：
Sen, Ayusman
中科院分区：
文献类型：
--
作者：
Mallouk, Thomas E.;Sen, Ayusman
© 2009美国科学公司www. SciAm。导致实验的假设是错误的。我们想象我们的纳米棒从它们的背部喷出微小的气泡，并被反冲力沿着推动。但他们实际上做的更有趣，因为它提醒纳米技术专家，我们必须以非常不同的方式思考小尺度上的运动。在宏观尺度上，反冲的概念是有道理的。当有人游泳或划船时，他们的胳膊、腿或桨将水向后推，而反冲力将身体或船向前推。这样，即使在停止推动之后，游泳者或船也可以向前滑行。一个物体能滑多远取决于粘性力或阻力，以及惯性，即物体对速度变化的阻力。阻力与物体的宽度成正比，而惯性与物体的质量成正比，而质量又与宽度的三次方成正比。对于较小的物体，惯性比阻力减小得快得多，变得可以忽略不计，所以阻力占了上风。在微米尺度上，任何滑动都在大约一微秒内结束，滑动距离小于百分之一纳米。因此，对于水中的微米级物体来说，游泳有点像在蜂蜜中涉水。纳米机器人对任何推它的东西都没有记忆，没有惯性，也没有惯性推进机制（如漂移），它将燃料分子中储存的能量转化为运动。我们从哈佛大学的勒斯特姆·伊斯马吉洛夫（Rustem Ismagilov）和乔治·怀特塞德斯（George Whitesides）在2002年报告的一种相当大的催化发动机中获得了灵感。哈佛大学的研究小组发现，船尾带有催化铂条的厘米级“船”会在装有水和过氧化氢（H2O2）的水箱表面自发移动。铂促使H2O2分解成氧气和水，形成的氧气气泡似乎通过反冲力推动船只前进，就像火箭后部排出的废气给它向前的推力一样。
© 2009 SCIENTIFIC AMERICAN, INC. www. SciAm. com SCIENTIFIC AMERICAN 73 pothesis that led to the experiment was wrong. We had imagined our nanorods spewing tiny bubbles off their back and being pushed along by recoil. But what they actually do is more interesting, because it reminds nanotechnologists that we must think very differently about motion on small length scales. At the macroscale, the notion of recoil makes good sense. When someone swims or rows a boat, their arms, legs or oars push water backward, and the recoil force pushes the body or boat forward. In this way, a swimmer or boat can glide forward even after one stops pushing. How far an object glides is determined by the viscous force, or drag, and by the inertia, a body’s resistance to changes in its velocity. The drag is proportional to the object’s width, whereas the inertia is proportional to the object’s mass, which in turn is proportional to the width to the third power. For smaller objects, inertia scales down much faster than drag, becoming negligible, so that drag wins out. On the micron scale, any gliding ends in about one microsecond, and the glide distance is less than one 100th of a nanometer. Hence, for a micronsize body in water, swimming is a bit like wading through honey. A nanomotor has no memory of anything that pushed on it—no inertia—and inertial propulsion schemes (such as drifting vert the energy stored in fuel molecules into motion. We took inspiration from a considerably larger catalytic motor reported in 2002 by Rustem Ismagilov and George Whitesides, both at Harvard University. The Harvard team had found that centimeter-scale “boats” with catalytic platinum strips on their stern would spontaneously move on the surface of a tank of water and hydrogen peroxide (H2O2). The platinum promoted the breakup of H2O2 into oxygen and water, and bubbles of oxygen formed that seemed to push the boats ahead by recoil, the way the exhaust coming out the back of a rocket gives it forward thrust.