Interfacial Mechanics and Contact Properties of Model Membranes

由PI领导的MERITA团队将开发一种高度敏感的粘合实验，旨在评估水中具有良好特征的模型表面之间的相互作用。这种测量是基于合成聚合物膜与石英晶体谐振器之间的接触。该膜由空气/水界面的弹性层组成，是从合成聚合物凝胶到生物组织等各种材料的极佳模型。膜表面和与其相互作用的表面都将涂上旨在消除两个表面之间非特定背景粘连的分子。然后，特定的粘合分子将被添加到两个表面，并且粘合能量将与单个键的相互作用势以及它们的表面浓度相关。这些实验在概念上类似于除湿实验，膜和表面的接触对应于接触表面之间基本上排除了水的区域。实验几何形状被设计成对非常小的接触角，从而对非常小的粘附性相互作用具有敏感性。膜弹性有两个重要的功能。第一个是扩大可以探测的粘结剂相互作用的范围，以便彻底研究软的、高度变形的材料的机械韧性的分子起源。薄膜弹性的第二个功能是提供一种将粘合剂分子固定在适当位置的方法，同时将系统与周围的空气环境隔离，以便即使在彼此机械接触的情况下，表面也保持水合。对于粘着能足够大以至于必须考虑弹性效应的情况，将进行详细的力学分析。有关机械接触性质的其他信息将通过监测晶体机械共振附近的石英晶体谐振器的频移和损耗来获得。实验方法可以应用于聚合物物理和生物学中的各种粘合问题，但实验将从利用在单分子水平上非常好地表征的粘合分子的研究开始。广泛的影响PI已经开发了一本独特的聚合物科学在线多媒体文本，将在本资金周期内继续进行修订。拟议的工作将直接对本科和本科教育做出额外贡献，三名博士生和6至8名本科生将接受力学、聚合物物理和聚合物合成各个方面的培训。作为与德国克劳斯塔尔大学Diethelm Johannsmann教授合作的一部分，还将获得国际经验。在这个项目的过程中，两名博士生将在约翰斯曼实验室进行研究，约翰斯曼实验室的两名学生将参观PI在西北大学的实验室。现有的外展活动将在埃文斯顿和芝加哥的当地高中和中学继续进行。拟议工作带来的机械表征能力的增强将使西北大学的各种研究小组受益，此外，当地公司的科学家和工程师也将利用由PI监督的微观力学实验室。这项工作的更广泛的科学影响将在生物材料领域感受到最强烈的感受，因为它提供了一种方法，用于量化实际相关的生物系统中服从于膜几何形状的粘附性。

Summary and Intellectual MeritA group led by the PI will develop a highly sensitive adhesion experiment designed to assessthe interactions between well characterized model surfaces in water. The measurement is basedon the contact between a synthetic polymer membrane and a quartz crystal resonator. Themembrane consists of an elastic layer at the air/water interface, and is an excellent model for avariety of materials ranging from synthetic polymer gels to living tissues. The membranesurface and the surface with which it interacts will both be coated with molecules that aredesigned to eliminate non-specific background adhesion between the two surfaces. Specificadhesion molecules will then be added to both surfaces, and the adhesion energy will be relatedto the interaction potential of the individual bonds, and to their surface concentration. Theexperiments are conceptually similar to dewetting experiments, with contact of the membraneand the surface corresponding to a region where water has been largely excluded from betweenthe contacting surfaces. The experimental geometry is designed to give sensitivity to very smallcontact angles, and hence to very small adhesive interactions. Membrane elasticity serves twoimportant functions. The first of these is to extend the range of adhesive interactions that can beprobed so that the molecular origins of mechanical toughness of soft, highly deformablematerials can be thoroughly investigated. The second function of membrane elasticity is toprovide a means for fixing the adhesive molecules in place while isolating the system from thesurrounding air environment so that the surfaces remain hydrated, even while in mechanicalcontact with one another. A detailed mechanical analysis will be developed for cases where theadhesion energy is large enough so that elastic effects must be taken into account. Additionalinformation about the nature of the mechanical contact will be obtained by monitoring thefrequency shift and dissipation of the quartz crystal resonators in the vicinity of a mechanicalresonance of the crystal. The experimental methodology can be applied to a wide variety ofadhesion problems in polymer physics and in biology, but experiments will begin with studiesutilizing adhesive molecules that are very well characterized at the single molecule level.Broader ImpactsThe PI has developed a unique online multimedia text in polymer science that will undergocontinued revision during this funding cycle. Additional contributions to undergraduate andundergraduate education will result directly from the proposed work, with three Ph.D. studentsand between 6 and 8 undergraduate students being trained in various aspects of mechanics,polymer physics and polymer synthesis. International experience will also be obtained as part ofa collaboration with Prof. Diethelm Johannsmann at the University of Clausthal in Germany.Two Ph.D. students will conduct research in the Johannsmann laboratory during the course ofthis project, and two students from the Johannsmann laboratory will visit the PI's lab atNorthwestern. Existing outreach activities will continue at local high schools and middle schoolsin Evanston and Chicago. The enhancements in mechanical characterization capabilitiesresulting from the proposed work will benefit a variety of research groups at Northwestern, inaddition to scientists and engineers at local companies who utilize the micromechanics labsupervised by the PI. The broader scientific impact of the work will be felt most strongly in thebiomaterials community, by providing a means for quantifying adhesion in practically relevantbiological systems that are amenable to the membrane geometry.