Effects of Curvature on Monolayer Morphology and Dynamics

CBET -1706378 PI：Zasadzinski，Joseph A.乳液，泡沫和其他多相系统（包括生物材料）的行为受到界面处表面活性分子（如磷脂和表面活性剂）的强烈影响。 世纪以来，人们一直用朗缪尔槽研究分子在平坦界面上的行为。 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工具来检查半径为30至500微米的气泡上分子单层的形态和动力学。 将使用共聚焦显微镜来确定单层的化学组成和单层中的分子排列如何受到气泡的弯曲表面的影响。 原子力显微镜和X射线衍射测量将有助于揭示曲率如何影响分子堆积。 对于尺寸以不同速率变化的气泡，将测量表面张力的变化。 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部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为重要。 结果也将有助于了解商业上重要的乳液和泡沫的稳定性和流变性，以及眼睛中泪膜的动态和接触镜的润湿行为。该项目将吸引所有学术水平的学生以及当地高中学生和教师参与。 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、液体状基质或两个不混溶的液体状相中形成共存的、有序的、固体状结构域。在朗缪尔槽的平坦界面上，固体域抵抗由于长程静电偶极-偶极排斥而聚结，即使可测量的线张力作用以使域周长最小化。最近的研究结果表明，对于小于200 µm的气泡，固相区域的连接性变为网状网络，流体相区域彼此分离和隔离。 固相的形态和连接性的这种变化改变了描述表面张力如何随界面面积变化的动态结晶模量。很少有人知道混合磷脂，蛋白质，脂肪酸和胆固醇单分子膜的膨胀模量的实验值。共聚焦显微镜将被用来成像高度弯曲的气泡表面，以确定如何界面曲率和单层组合物改变域形态，和一个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的动态结晶模量。 单层中的横向相分离对于临床和天然肺表面活性剂是典型的。拉普拉斯压力表明，如果表面张力恒定，则不同半径的相互连接的气泡或肺泡最多是亚稳定的。然而，如果界面弹性模量足够大，则对界面压缩的抵抗力可以克服拉普拉斯压力并稳定互连的肺泡。因此，双折射模量以及它如何取决于单层组成、形态、界面曲率和界面面积的变化对肺稳定性至关重要。

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.