Flow and rheology of interfaces at microscopic length scales

微观长度尺度下界面的流动和流变学

• 批准号: 0853837
• 负责人: Eric Weeks
• 金额: $ 25.22万
• 依托单位: Emory University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-01 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0853837&HistoricalAwards=false
• 关键词: Flow; rheology; interfaces; microscopic; length

0853837Weeks Viscoelastic interfaces are ubiquitous in nature; such as in cell membranes and in the alveoli of the lung, and can be artificially constructed; such as in emulsions/foams and soap films. Determining their rheology is, therefore, critical to our understanding of the dynamics of many processes that occur at these interfaces. Furthermore, this knowledge may help in the design of better materials for industrial applications, particularly in the food and cosmetics sector. In this project, the PIs will investigate the use of microscopic particles (diameters 20 nm - 2 microns) as probes of the viscoelasticity, and obtain the surface viscosity and elasticity by observing the thermal Brownian motion of the particles. Because of the size of the probes, this method is more sensitive than most interfacial rheology techniques that currently exist. By correlating the Brownian motion of pair of particles at different separations, they also will measure length-scale dependent viscoelasticity. This will relate the bulk properties of interfaces with their microstructure and dynamics, an approach that is lacking in other techniques. They plan to apply our method to: a) Systems with extremely low surface viscosity; specifically phospholipid molecules at an air water interface. Accurate measurements of surface viscosities below 10-8 Pa-s-m do not currently exist. b) Systems that have spatially heterogeneous domains, and therefore surface rheology that depends on the size of these domains. They will create these domains by applying surface pressure to phospholipids and fatty acids, and measure their length scale dependent rheology. c) Soap film hydrodynamics; the motion of a probe particle creates a flow field affecting the motion of other particles. Correlating the motion of particles by our technique, we will be able to measure this flow field. Further, The PI plans to actively perturb these interfaces by applying a known force to the probe particles. The drag experienced by the particles in response to the force is a direct measure of the viscoelasticity. By applying large forces to a particle, they will obtain the non linear response of the interface, which will be of fundamental importance and will have industrial relevance as well. Broad Impact: Viscoelastic interfaces are ubiquitous in nature; such as in cell membranes and in the alveoli of the lung, and can be artificially constructed; such as in emulsions/foams and soap films. Determining their rheology is therefore critical to our understanding of the dynamics of many processes that occur at these interfaces. Further, this may help in the design of better materials for industrial applications, particularly in the food and cosmetics sector. The PI will conduct at least one field trip each year, for groups of primary school students. We have done these in the past; these field trips give students hands on laboratory experiences. In particular, they plan to develop new activities around interfaces such as soap films (and foams in general). These field trips generally take everybody in our laboratory group one day of time (including preparation, interacting with the students, and cleaning up). The PI has an extensive commitment to undergraduate research, and has mentored 18 undergraduate researchers in our laboratory over the past five years. They plan to continue this by working with at least one undergraduate per year on this research, and possibly two per year (as often students work during the school year for academic credit). These undergraduates, and also the graduate student involved, will learn microscopy skills, computer data analysis, and some wet lab chemistry, providing useful experiences for whatever career directions they choose.

0853837周粘弹性界面在自然界中普遍存在;例如在细胞膜和肺泡中，并且可以人工构建;例如在乳液/泡沫和肥皂膜中。因此，确定它们的流变性对于我们理解这些界面上发生的许多过程的动力学至关重要。此外，这些知识可能有助于设计更好的工业应用材料，特别是在食品和化妆品领域。在本项目中，PI将研究使用微观颗粒（直径20 nm - 2微米）作为粘弹性探针，并通过观察颗粒的热布朗运动获得表面粘度和弹性。由于探针的尺寸，这种方法比目前存在的大多数界面流变学技术更灵敏。通过关联不同间距下粒子对的布朗运动，他们还将测量长度尺度依赖的粘弹性。这将与他们的微观结构和动力学，在其他技术中缺乏的方法，界面的整体性能。他们计划将我们的方法应用于：a）具有极低表面粘度的系统;特别是空气-水界面处的磷脂分子。目前尚不存在低于10-8 Pa-s-m的表面粘度的精确测量。B）具有空间上不均匀的区域的系统，因此表面流变性取决于这些区域的尺寸。他们将通过对磷脂和脂肪酸施加表面压力来创建这些域，并测量其长度尺度依赖的流变学。c）皂膜流体动力学;探针颗粒的运动会产生影响其他颗粒运动的流场。用我们的技术把粒子的运动联系起来，我们就能测量这个流场。此外，PI计划通过向探针粒子施加已知的力来主动扰动这些界面。颗粒响应于力而经受的阻力是粘弹性的直接量度。通过对粒子施加大的力，他们将获得界面的非线性响应，这将是非常重要的，也将具有工业相关性。广泛影响：粘弹性界面在自然界中普遍存在;例如在细胞膜和肺泡中，并且可以人工构建;例如在乳液/泡沫和肥皂膜中。因此，确定它们的流变性对于我们理解在这些界面处发生的许多过程的动力学至关重要。此外，这可能有助于为工业应用设计更好的材料，特别是在食品和化妆品领域。PI每年将为小学生团体进行至少一次实地考察。我们在过去已经做过这些;这些实地考察让学生动手实验室的经验。特别是，他们计划围绕肥皂膜（和一般泡沫）等界面开展新的活动。这些实地考察通常需要我们实验组的每个人一天的时间（包括准备，与学生互动和清理）。 PI对本科生研究有着广泛的承诺，在过去的五年里，我们实验室指导了18名本科生研究人员。他们计划继续这项研究，每年至少与一名本科生合作，可能每年两名（因为学生经常在学年中工作以获得学分）。这些本科生，也是研究生参与，将学习显微镜技术，计算机数据分析，和一些湿实验室化学，为他们选择的任何职业方向提供有用的经验。