Studies of Viscophoresis -- Drift in a Viscosity Gradient

非技术摘要：通过在充满液体的管的两端施加压力，电压或温度差，我们可以使其中的流体或小颗粒移动，并且运动的机制已经很好地理解。 最近发现，当一个小玻璃管充满液体，并且两端的粘度保持在不同的值时，电流开始流动;电荷运动的起源目前还不清楚。该项目通过测量纳米流体通道内盐离子和小荧光颗粒的运动来实验性地研究这种现象的起源，在纳米流体通道中，可以仔细控制液体的物理尺寸和性质。这些结果为布朗运动理论提供了新的线索--布朗运动是小颗粒与液体分子碰撞引起的随机运动。值得注意的是，在爱因斯坦著名的布朗运动理论发表后的世纪里，粒子是否以粘性梯度漂移，如果是，朝哪个方向漂移的问题仍然存在争议。布朗运动的传统图像是一个随机方向的步行，步长与粘度成反比。 当粘性在空间中变化时，人们必须选择随机游走中每一步的大小是否对应于该步开始时的粘性，该步结束时的粘性，或者介于两者之间的某个地方，这个看似无关紧要的选择具有可测量的后果。 事实上，在不同的身体状况下，不同的选择是合适的。实验可以解决这一争论，并加深我们对活细胞中重要的微观现象的理解，在工业应用中，甚至可能超越。该团队正在制作一幅科学漫画，向广大非专业观众解释布朗运动及其基本重要性。技术摘要：该项目正在探索最近发现的纳米流体传输现象的起源，即溶液中的小颗粒由于溶剂粘度的梯度而漂移。该团队将这种运输现象命名为“visophoresis”。在具有明确尺寸的纳米流体装置中的离子和荧光量子点的传输的测量建立漂移速度、粘度梯度和其他实验参数之间的定量关系。需要这些实验的结果来阐明长期存在的"伊藤-斯特拉托诺维奇"理论问题，即具有乘性噪声的噪声驱动动力学。粘渗是重要的，因为纳米流体传输过程在生物学、地质学以及微流体和纳米流体技术中起着至关重要的作用。该项目可以在那些经常出现大粘度梯度的领域中产生新的见解或应用。该项目为研究生提供了一个极好的培训机会，并正在制作一个教育科学漫画，以达到广泛的非专业观众。该奖项反映了NSF的法定使命，并已被认为是值得支持的，通过评估使用基金会的智力价值和更广泛的影响审查标准。

Non-technical Abstract:By applying a difference in pressure, voltage, or temperature to the ends of a tube filled with liquid, we can cause the fluid or small particles within it to move, and the mechanisms underlying the motion are well understood. It was recently discovered that when a small glass tube is filled with liquid and the viscosity is held at different values at either end, an electrical current begins to flow; the origin of that motion of electrical charges is not understood at present. This project is experimentally investigating the origins of that phenomenon by measuring the motion of salt ions and small fluorescent particles inside nanofluidic channels, where the physical dimensions and the properties of the liquid can be carefully controlled. The results shed new light onto the theory of the Brownian motion - the random motion of small particles caused by its collisions with the molecules of a liquid. Remarkably, more than a century after the publication of Einstein's famous theory of Brownian motion, the question of whether a particle drifts in a viscosity gradient, and if so, in which direction, is still debated. The conventional picture of the Brownian motion is a walk with steps taken in random directions and step sizes that are inversely proportional to the viscosity. When the viscosity varies in space, one must choose whether the size of each step in the random walk corresponds to the viscosity at the beginning of the step, the end of the step, or somewhere in between, and this seemingly insignificant choice has measurable consequences. In fact, different choices can be appropriate in different physical situations. Experiments can settle the debate and deepen our understanding of microscopic phenomena that are important in living cells, in industrial applications, and possibly beyond. The team is producing a scientific cartoon to explain the Brownian motion and its fundamental importance to a broad audience of non-specialists. Technical Abstract:This project is exploring the origins of a recently discovered nanofluidic transport phenomenon whereby small particles in solution drift due to a gradient in the viscosity of the solvent. The team has named this transport phenomenon "viscophoresis". Measurements of the transport of ions and fluorescent quantum dots in nanofluidic devices with well-defined dimensions establish the quantitative relationships between the drift velocity, the viscosity gradient, and other experimental parameters. The results of those experiments are needed to shed new light on the longstanding "Ito-Stratonovich" theoretical problem of noise-driven dynamics with multiplicative noise. Viscophoresis is significant because nanofluidic transport processes play a vital role in biology, in geology, and in micro- and nanofluidic technology. This project can lead to new insights or applications in those domains, where large viscosity gradients frequently arise. This project provides an excellent training opportunity for a graduate student, and an educational scientific cartoon is being created to reach a broad audience of non-specialists.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.