ISS: Active Liquid-Liquid Phase Separation in Microgravity

液-液相分离是一种普遍存在的现象，在物理学、材料科学、工程学、生物学和日常生活中发挥着核心作用。两液相被软界面分开，软界面受重力的影响很大，容易受到热波动或外部流动的影响而变形。日常经验表明，温和的振动如何诱导软界面的波动，而更严格的振动则重新初始化相分离动力学。活性物质提供了一种通过微观耗能成分的集体运动来产生流体流动的替代方法。基于活性物质的内部产生的流动如何耦合到软界面和相关的液-液相分离仍然是一个悬而未决的问题。基于地面的研究显示了有趣的行为，但引力抑制了大规模变形和对可能行为的充分探索。这个项目的重点是发展对活动界面的定量理解。从更广泛的角度来看，该项目将培养本科生进行跨学科研究，并为高中学生开发以软材料、液-液相分离和微重力研究为主题的丰富课程提供支持。该项目的研究目标分为三个相辅相成的目标，这将大大增加对主动液-液相分离和相关活动界面的理解。在第一个目标中，将创造毫米大小的软界面，将大量活性流体与被动聚合物悬浮液分开。这项研究将确定重力如何影响肉眼可见的活跃波动和相关的行波。该项目还将研究宏观界面如何解体以产生活性乳状液，这一转变受到重力的抑制，但在微重力环境中应该是可以观察到的。在第二个目标中，该项目将从一个统一的初始状态开始，并研究活性液滴粗化的动力学。微重力将使我们的样品呈现真正的二维。最后，在第三个目标中，将研究重力影响，以确定当活性流体沿边界爬升时，如何发生活性润湿转变。获得的数据将严格测试主动应力如何耦合到柔软的可变形表面的理论模型。这类模型对于构建合成机械原生细胞至关重要，并可能与我们对生物学的理解相关。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Liquid-liquid phase separation is a pervasive phenomenon that plays a central role throughout physics, material science, engineering, biology, and everyday life. Two liquid phases are separated by soft interfaces that are greatly affected by gravitational forces and are easily deformed either by thermal fluctuation or by external flows. Everyday experience demonstrates how gentle shaking induces waves of a soft interface, while more rigorous shaking reinitializes the phase separation dynamics. Active matter provides an alternative method of generating fluid flows through the collective motion of microscopic energy-consuming constituents. It remains an open question of how active matter-based internally-generated flows couple to the soft interfaces and the associated liquid-liquid phase separation. Ground-based research indicates intriguing behaviors, but gravitational forces suppress large-scale deformation and full exploration of the possible behaviors. This project is focused on developing a quantitative understanding of the active interfaces. From a broader perspective, this project will train undergraduate students in interdisciplinary research, and provide support for developing a curriculum-enriching Saturday course for high school students that is centered around the topic of soft materials, liquid-liquid phase separation, and microgravity research.The research goals of this project are divided into three complementary aims, which will greatly increase understanding of active liquid-liquid phase separation and associated active interfaces. In the first aim, millimeter-sized soft interfaces will be created that separate a bulk active fluid from a passive polymer suspension. The research will determine how gravity influences active fluctuations and associated traveling waves, which are visible by the naked eye. The project will also study how a macroscopic interface disintegrates to generate an active emulsion, a transition that is suppressed by gravity but should be observable in a microgravity environment. In the second aim, the project will start with a uniform initial state and study the dynamics of coarsening active droplets. Microgravity will render our samples truly two-dimensional. Finally, in the third aim, gravity affects will be studied to determine how the active wetting transition that occurs when active fluid climbs along a boundary. The acquired data will rigorously test theoretical models of how active stresses couple to soft deformable surfaces. Such models are essential for building synthetic mechanical protocells and might have relevance to our understanding of biology.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.