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The Transpiration Of Water At Negative Pressures In A Synthetic Tree

机译：合成树中负压下水的蒸腾作用

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摘要

Plant scientists believe that transpiration-the motion of water from the soil, through a vascular plant, and into the air-occurs by a passive, wicking mechanism. This mechanism is described by the cohesion-tension theory: loss of water by evaporation reduces the pressure of the liquid water within the leaf relative to atmospheric pressure; this reduced pressure pulls liquid water out of the soil and up the xylem to maintain hydration. Strikingly, the absolute pressure of the water within the xylem is often negative, such that the liquid is under tension and is thermodynamically metastable with respect to the vapour phase. Qualitatively, this mechanism is the same as that which drives fluid through the synthetic wicks that are key elements in technologies for heat transfer5, fuel cells and portable chemical systems. Quantitatively, the differences in pressure generated in plants to drive flow can be more than a hundredfold larger than those generated in synthetic wicks. Here we present the design and operation of a microfluidic system formed in a synthetic hydrogel. This synthetic 'tree' captures the main attributes of transpiration in plants: transduction of subsa-turation in the vapour phase of water into negative pressures in the liquid phase, stabilization and flow of liquid water at large negative pressures (- l.0MPa or lower), continuous heat transfer with the evaporation of liquid water at negative pressure, and continuous extraction of liquid water from subsaturated sources. This development opens the opportunity for technological uses of water under tension and for new experimental studies of the liquid state of water.
机译：植物科学家认为，蒸腾作用是水从土壤到维管束植物的运动，它是通过被动的芯吸机制发生的。内聚张力理论描述了这种机制：由于蒸发而损失水，相对于大气压降低了叶内液态水的压力；这种降低的压力将液态水从土壤中拉出并向上木质部保持水分。引人注目的是，木质部中水的绝对压力通常是负的，使得液体处于张力下并且相对于气相是热力学上亚稳态的。从本质上讲，这种机制与通过合成油芯驱动流体的机制相同，合成油芯是传热技术，燃料电池和便携式化学系统中的关键要素5。从数量上讲，植物产生的驱动流动压力差可能比合成油芯产生的压力差大一百倍。在这里，我们介绍在合成水凝胶中形成的微流控系统的设计和操作。这种合成的“树”体现了植物蒸腾作用的主要属性：将水蒸气中的亚结构转换成液相中的负压，在较大的负压（-1.0 MPa或更低）下稳定和使液态水流动），在负压下蒸发液态水并进行连续传热，并从不饱和源连续提取液态水。这一发展为在张力下使用水的技术用途以及对水的液态状态进行新的实验研究提供了机会。

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  • 来源
    《Nature》 |2008年第7210期|p.208-212|共5页
  • 作者

    Tobias D. Wheeler; Abraham D. Stroock;

  • 作者单位

    School of Chemical and Biomolecular Engineering, Cornell University, ithaca, New York 14853, USA;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 自然科学总论;
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