CAREER: Fundamental Studies to Advance the Science and Engineering of Water at Negative Pressures

内容提要：推进负压下水的科学和工程的基础研究CBET-0747993康奈尔大学学术价值：这项建议的目的是将液态水的知识和潜在的实际用途提供到一个只有少数实验探索和几乎完全没有技术开发的物理状态中：负压下液态水的机械稳定和热力学亚稳状态。众所周知，液态水的强度非常大：植物在蒸腾过程中，压力可降至-10兆帕；在实验室，液态水被置于-102兆帕的压力下。然而，人类技术从来没有在显著的负压(即-1.5兆帕)下开采过水。负压状态也蕴藏着有关水在整个液体状态下性质的突出奥秘的重要信息：分子模型表明，热力学和动力学异常不仅在这种状态下持续存在，而且变得更加戏剧性，与流体的不寻常的分子属性紧密地耦合在一起。尽管科学界非常感兴趣，但水在负压下的热力学、动力学和结构性质实际上还没有通过实验绘制出来。由于先进制造工具的出现和我们实验室最近开发的一种新方法，基于液态水通过分子膜与亚饱和蒸汽的热力学耦合，将液态水深入负压区域，这一实验工作已经成熟。研究人员将利用这些工具建立一个微流控平台，利用该平台以前所未有的精度操纵和研究张力下的水。他们的研究将描绘水的拉伸状态的热力学、动力学和结构性质，重点是阐明宏观性质的分子起源。这些测量将使他们能够解决有关液态水性质的一些最深层次的悬而未决的问题，并填补这种不寻常状态物质的科学和工程知识基础上的一个重大空白。这一努力也是及时的，因为它将创建一个动态界面，以适应水计算模型的快速发展(见合作信函)。更广泛的影响：这项研究有可能为水管理技术开辟一种新的运行机制：热管、土壤芯环境修复、用于分离和提纯的微流控芯片实验室系统，以及低温燃料电池的呼吸电极。在所有这些技术中，芯子或薄膜都被用来在正压或非常轻微的负压(-0.1兆帕)下调节水的流动，而功能因无法在极大的张力下控制水而受到严重限制。基于这里提出的发展，这些传质速率可以增加几个数量级，操作参数(尺寸、温度、相对湿度)的范围可能会显著扩大。当今工程师的应用程序发生了令人兴奋的变化，这就要求更新课程设置和教学模式。这位研究人员描述了修改现有课程组成部分并在本科生和研究生层面增加新课程的计划。提出了应对现代工程课程中关键挑战的计划：1)保持基本概念的有效教学，同时更新背景，包括更多与微化学技术和生物工程等新背景相关的材料；2)鼓励创新地使用技能，以便未来的工程师准备发明和操作下一代技术；以及3)鼓励研究，将其作为本科生和研究生教育的重要组成部分，并作为职业选择。随着新技术的出现，还必须教育公众，特别是儿童，了解其功能的永恒(例如热力学)和及时(例如微米和纳米技术)方面。在第七节中，我建议开发一套演示、演示和教材，利用水的非凡特性来激发体验式科学学习。这些材料将与康奈尔材料科学中心(见Letter)、费城富兰克林研究所和伊萨卡科学中心的推广计划合作开发和展示。这些合作将使人们能够与来自广泛的社会经济规模和代表性不足的群体进行互动。

ABSTRACTCAREER: Fundamental Studies to Advance the Science and Engineering of Water at Negative Pressures CBET- 0747993 Cornell UniversityIntellectual merit: The objectives of this proposal are to provide knowledge and potential practical use of liquid water into a physical regime that has been only sparsely explored experimentally and nearly entirely unexploited technologically: the mechanically stable and thermodynamically metastable state of liquid water at negative pressures. Liquid water is known to be very strong: plants have been shown to move water during transpiration at pressures down to -10 MPa; in the laboratory, it has been placed at pressures -102 MPa. Nonetheless, no human technology has ever exploited water at significant negative pressures (i.e., -1.5 MPa). The negative pressure regime also harbors important information about the outstanding mysteries of water's properties throughout the liquid state: molecular models indicate that the thermodynamic and dynamic anomalies not only persist in this regime but also become more dramatic and tightly coupled to the unusual molecular properties of the fluid. Despite significant interest from the scientific community, the thermodynamic, dynamic, and structural properties of water at negative pressures have been virtually uncharted by experiment. This experimental effort is ripe for undertaking due to the emergence of advanced fabrication tools and recent developments in our laboratory of a new method to drive liquid water deep into the negative pressure regime based on thermodynamic coupling of liquid water to a sub-saturated vapor through molecular membranes. The investigator will exploit these tools to build a microfluidic platform with which to manipulate and study water under tension with unprecedented precision. Their studies will map thermodynamic, dynamic, and structural properties of the stretched state of water with an emphasis on elucidating the molecular origins of macroscopic properties. These measurements will allow them to address some of the deepest outstanding questions about the nature of the liquid water and to fill a major gap in the foundation of knowledge for the science and engineering of this unusual state of matter. This effort is also timely, as it will create a dynamic interface with the rapidly progressing developments in computational modeling of water (see letters of collaboration). Broader Impact: This research has the potential to open a new regime of operation for water management technologies: heat pipes, soil wicks environmental remediation, microfluidic lab-on-a-chip systems for separations and purifications, and breathing electrodes for low temperature fuel cells. In all of these technologies, wicks or membranes have been used mediate the flow of water at positive or very slightly negative pressures (-0.1 MPa), and function is severely limited by the inability to control water under substantial tension. Based on the developments proposed here, these rates of mass transfer could be increased by orders of magnitude and ranges of operational parameters (size, temperature, relative humidity) could be dramatically broadened. Exciting changes in the applications of today's engineers create an obligation to update the curriculum and the modes by which it is taught. The investigator describes plans to modify existing components of the curriculum and add new ones at both the undergraduate and graduate levels. Plans are proposed that address critical challenges in modern engineering curricula: 1) the maintenance of effective teaching of fundamental concepts while updating the context to include more material relevant to new contexts such as microchemical technology and bioengineering, 2) the encouragement of innovative use of skills, such that future engineers are poised to invent as well as operate the next generation of technology, and 3) the encouragement of research as a vital component of both undergraduate and graduate education and as a career option. As new technologies emerge, it is also important to educate the public, and, in particular, children on both the timeless (e.g., thermodynamics) and the timely (e.g., micro and nanotechnology) aspects of their function. In Section VII, I propose the development of a set of presentations, demonstrations, and teaching materials that exploit the extraordinary properties of water to motivate experiential science learning. These materials will be developed and presented in collaboration with the outreach program of the Cornell Center for Material Science (see letter), the Franklin Institute of Philadelphia, and the Ithaca Sciencenter. These collaborations will enable interaction with people from a broad range of socio economic scales and underrepresented groups.