Effects of Curvature on Monolayer Morphology and Dynamics

乳液、泡沫和其他多相体系的行为，包括生物材料，受到界面上的表面活性分子，如磷脂和表面活性剂的强烈影响。一个多世纪以来，分子在平面界面上的行为一直在使用朗缪尔槽进行研究。然而，在多相体系中，大多数界面是弯曲的，这影响了界面上分子的分布和界面的性质。该奖项将支持使用新的工具来研究半径从30微米到500微米的气泡上分子单分子膜的形态和动力学。共聚焦显微镜将被用来确定单层的化学成分和单层中的分子排列如何受到气泡曲面的影响。原子力显微镜和X射线衍射测量将有助于揭示分子堆积是如何受曲率影响的。对于大小以不同速率变化的气泡，将测量其表面张力的变化。这项研究的结果将有助于解释界面曲率对单层的影响如何影响肺内弯曲液体表面的稳定性，这在疾病或创伤引起的肺部炎症中尤其重要。研究结果还将有助于了解具有重要商业价值的乳液和泡沫的稳定性和流变性、泪膜在眼睛中的动态变化以及隐形眼镜的润湿行为。该项目将吸引所有学术水平的学生，以及当地的高中学生和教师。将准备包含研究图像的教学模块，以说明材料特性对肺部健康的重要性。磷脂、胆固醇和脂肪酸或醇的单层可以在连续的、无序的类液体基质或两个不相容的类液体相中形成共存的、有序的类固体结构域。在朗缪尔槽的平坦界面上，由于长程静电偶极-偶极斥力，即使可测量的线张力起到最小化磁区周长的作用，固体磁区也会阻止合并。最近的结果表明，对于小于200µm的气泡，固相域的连接性转变为网状网络，而流体相域彼此断开和隔离。这种固相形态和连接性的变化改变了动态膨胀系数，它描述了表面张力如何随界面面积变化。关于混合磷脂、蛋白质、脂肪酸和胆固醇单分子膜的膨胀系数实验值知之甚少。共焦显微镜将被用来成像高度弯曲的气泡表面，以确定界面曲率和单层组成如何改变结构域形态，而新的毛细管压力微张力计将被用来测量这种形态如何影响动态膨胀模数。单层的横向相分离对于临床和天然肺表面活性物质是典型的。拉普拉斯压力表明，如果表面张力不变，不同半径的相互连接的气泡或肺泡充其量是亚稳定的。然而，如果扩张模数足够大，对界面压缩的抵抗可以克服拉普拉斯压力，稳定相互连接的肺泡。因此，扩张模数及其与单层组成、形态、界面曲率和界面面积变化的关系对肺的稳定性至关重要。

CBET - 1706378PI: Zasadzinski, Joseph A.The behavior of emulsions, foams, and other multiphase systems, including biological materials, is strongly affected by surface-active molecules, such as phospholipids and surfactants, at interfaces. For more than a century, the behavior of molecules at flat interfaces has been studied using a Langmuir trough. However, most interfaces in multiphase systems are curved, which affects the distribution of the molecules on the interface and the properties of the interface. This award will support the use of new tools to examine the morphology and dynamics of molecular monolayers on bubbles with radii from 30 to 500 microns. A confocal microscope will be used to determine how the chemical composition of the monolayer and molecular arrangements in the monolayer are affected by the curved surface of the bubble. Atomic force microscopy and X-ray diffraction measurements will help reveal how molecular packing is affected by curvature. Variations in surface tension will be measured for a bubble whose size is changed at different rates. Results from this research will help explain how effects of interfacial curvature on monolayers influence the stability of curved liquid surfaces in the lung, which is especially important in lung inflammation resulting from disease or trauma. Results will also be useful in understanding the stability and rheology of commercially important emulsions and foams and the dynamics of tear films in the eye and wetting behavior of contact lenses. The project will engage students at all academic levels, as well as local high-school students and teachers. Instructional modules containing images from the research will be prepared to illustrate the importance of material properties on lung health. Monolayers of phospholipids, cholesterol, and fatty acids or alcohols can form coexisting, ordered, solid-like domains in a continuous, disordered, liquid-like matrix, or two immiscible liquid-like phases. On the flat interface of a Langmuir trough, the solid domains resist coalescence due to a long-range electrostatic dipole-dipole repulsion even though a measurable line tension acts to minimize the domain perimeter. Recent results suggest that for bubbles smaller than 200 µm, the connectivity of the solid phase domains changes to a mesh-like network with the fluid phase domains disconnected and isolated from each other. This change in morphology and connectivity of the solid phase alters the dynamic dilatational modulus, which describes how the surface tension changes with interfacial area. Very little is known about experimental values of the dilatational modulus of mixed phospholipid, protein, fatty acid and cholesterol monolayers. Confocal microscopy will be used to image highly curved bubble surfaces to determine how interfacial curvature and monolayer composition alter the domain morphology, and a new capillary pressure microtensiometer will be used to measure how this morphology influences the dynamic dilatational modulus. Lateral phase separation in monolayers is typical for clinical and native lung surfactants. The Laplace pressure suggests that interconnected bubbles or alveoli of different radii are, at best, metastable if the surface tension is constant. However, if the dilatational modulus is sufficiently large, resistance to interfacial compression can overcome the Laplace pressure and stabilize interconnected alveoli. Hence, the dilatational modulus, and how it depends on monolayer composition, morphology, interfacial curvature and changes in interfacial area are essential to lung stability.