Diamagnetic levitation for studies of fluids and granules in weightless conditions, and for interdisciplinary science

物体在失重时是如何运动的？这是一个吸引了几代科学家和公众想象力的问题。为了解决这一对太空旅行至关重要的问题，人们在航天器、绕地球轨道飞行或自由落体中进行实验。抗磁悬浮是一种利用电磁铁产生的强磁场模拟地球轨道失重状态的技术。它允许反磁性材料，如水和生物有机体，悬浮在磁铁上方。这些物质被磁场排斥，但太弱了，通常无法注意到，不像铁，它被磁场强烈吸引。就像离心力平衡轨道宇宙飞船的重量一样，反磁力对抗悬浮物体上的重力，因此它就像在太空中一样漂浮。1863年，Plateau受到启发，在酒精混合物中漂浮的旋转油滴上进行实验，以模拟地球的形状。他认识到，表面张力将水滴保持在一起，可以模拟引力将行星或星星保持在一起的作用。后来人们意识到，带电液滴的表面张力也可以模拟原子核内束缚核子的力。我将使用DL来研究高原无法研究的东西：一滴自由悬浮在太空中的水滴。我将研究利用这一滴来发现天体和原子核行为线索的可能性。通过研究液滴的振动，我也将获得它的表面张力。这种非接触式测量技术将使非常活泼的液体和过冷液体的研究成为可能。我还将研究悬浮的“雨滴”如何在电场中振动、扭曲和破碎，从而影响电风暴的行为，并对破碎后从水滴中喷出的小水滴进行成像。后一个过程对于从液体中提取生物分子进行分析非常重要，为约翰·芬恩（John Fenn）赢得了2002年诺贝尔奖，并彻底改变了新药物的寻找。颗粒状材料无处不在，从小行星到玉米片。了解颗粒的动力学在许多行业（例如食品和制药）以及研究许多自然过程（例如滑坡）中非常重要。在零重力下，颗粒总是悬浮在液体中。振动液体导致颗粒移动并自组织成三维图案，这是由颗粒周围的液体运动引起的。我将对悬浮颗粒进行实验，以研究颗粒和液体之间的相互作用;这些知识最终将导致在地球和太空中控制和利用颗粒材料的显着改进。通过与其他研究人员合作，我还将探索DL如何应用于更广泛的主题。我将用它来获得生物组织在强磁场中磁化强度的精确测量，这对医学磁共振成像至关重要。在传统方法中，样品容器的磁化会给测量带来很大的不确定性。由于悬浮样品不需要容器，我们避免了这种复杂性。我将研究气泡在悬浮气体饱和液体中的成核和生长，这将直接有助于我们对潜水事故中的减压病（“弯曲”）的理解。通过悬浮液体，我们可以观察到不断增长的气泡，而不会脱离其成核位置并漂浮。我还将研究如何使用强磁场在悬浮溶液中构建中空管状蛋白质结构的网格，这可以形成纳米级电路的模板或细胞生长的“支架”。

How do objects behave when they are weightless? This is a question that has fascinated generations of scientists and captured the imagination of the general public. To address this question of fundamental importance for space travel, experiments are performed in space-craft, orbiting the Earth, or in free-fall. Diamagnetic levitation (DL) is a promising technique that uses a powerful magnetic field generated by an electromagnet, to simulate the weightless conditions in orbit, on the Earth. It allows diamagnetic materials, such as water and biological organisms, to levitate above the magnet. These materials are repelled from the magnetic field, but too weakly to notice ordinarily, unlike iron for example, which is strongly attracted to the field. Just as the centrifugal force balances the weight of an orbiting spaceship, the diamagnetic force opposes the force of gravity on a levitated object, so that it floats as though in space. In 1863, Plateau was inspired to experiment on a spinning drop of oil, floated in an alcohol mixture, to model the Earth's shape. He recognised that surface tension, holding the drop together, could model the action of gravity holding a planet or star together. It was later realised that the surface tension of an electrically-charged drop could also model the forces binding nucleons inside an atomic nucleus. I will use DL to study what Plateau couldn't: a drop suspended freely in space. I will investigate the possibility of using this drop to discover clues to the behaviour of both astronomical objects and the atomic nucleus. By studying vibrations of the drop, I will also obtain its surface tension. This non-contact measurement technique will enable the study of very reactive liquids and supercooled liquids.I will also study how levitated 'rain' drops vibrate, distort and shatter in electric fields, which influences the behaviour of electrical storms, and image the spray of small droplets that issue from the drop upon break-up. The latter process is important in extracting biological molecules from liquids for analysis, winning John Fenn a Nobel Prize in 2002, and revolutionising the search for new medicinal drugs.Granular materials are everywhere, from asteroids to cornflakes. Understanding the dynamics of the granules is important in many industries, e.g. food and pharmaceutics, and in studying many natural processes, e.g. landslides. In zero-gravity, granules are always suspended in the liquid. Vibrating the liquid causes granules to move and self-organise into three-dimensional patterns, caused by the motion of the liquid around the grains. I will perform experiments on levitated granules to investigate the interactions between the grains and the liquid; such knowledge should ultimately lead to significant improvements in the control and exploitation of granular materials on Earth and in space. By collaborating with other researchers, I will also explore how DL can be applied to a broader range of topics. I will use it to obtain precise measurements of the magnetisation of biological tissues in a strong magnetic field, fundamentally important for medical magnetic resonance imaging. In conventional methods, the magnetisation of the sample container introduces significant uncertainty into the measurement. Since a levitated sample does not require a container, we avoid this complication. I will study the nucleation and growth of bubbles in levitating gas-saturated liquids, directly benefitting our understanding of, e.g. decompression sickness ('the bends') in SCUBA accidents. By levitating the liquid, we can observe the growing bubble without it detaching from its nucleation site and floating away. I will also investigate how a strong magnetic field can be used to construct a mesh of hollow tubular protein structures in levitating solutions, which could form templates for nano-scale electric circuits or 'scaffolds' for cell growth.