Non-Equilibrium Systems: Spreading, Deformation, Adhesion and Friction

非平衡系统：扩散、变形、粘附和摩擦

• 批准号: 0454947
• 负责人: Mark Robbins
• 金额: --
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-06-15 至 2010-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0454947&HistoricalAwards=false
• 关键词: Non; Equilibrium; Systems; Spreading; Deformation

TECHNICAL EXPLANATION This research addresses fundamental non-equilibrium processes that impact many technologies: spreading, plastic deformation, adhesive failure and friction. Traditional engineering approaches to these phenomena start from macroscopic continuum equations with phenomenological constitutive relations and boundary conditions whose validity is questionable, particularly as dimensions approach the molecular scale. Molecular simulations will be used to test existing continuum descriptions, provide connections between molecular interactions and macroscopic behavior, develop new mesoscale models, and provide input for macroscopic models that cannot be obtained from experiment. Simulations of spreading will study the singular stresses that are predicted to exist near the contact line where a fluid interface intersects a solid. Several competing mechanisms have been proposed for removing the singularity and it is difficult to distinguish between them using experiments. Molecular dynamics and hybrid atomistic/continuum methods will be used to test new theories based on diffusion and variations in interfacial tension. The results will enable construction of mesoscale models for larger length and time scales. These will be applied to dynamics in more complex geometries to study contact angle hysteresis and multi-phase flow in porous media.NON-TECHICAL EXPLANATION Studies of deformation, adhesion and friction will focus on amorphous polymer glasses, which are a major component of many adhesives and structural materials. The connectivity of the molecules leads to entanglements that dramatically alter mechanical properties, particularly at large strains. A new method will be used to visualize entanglements and correlate their evolution to stress/strain curves during craze formation and shear deformation. Atomistic and hybrid atomistic/continuum simulations will be used to study the fracture energy and mechanisms in bulk and thin films. Different polymers will be studied to determine what aspects of molecular interactions select the failure mode. Work on friction will explore the relation between constitutive relations for friction and bulk deformation, the contrast between nanoscale and macroscopic friction coefficients for some polymers, and the effect of molecular alignment near the surface on friction.Intellectual Merit: The proposed research addresses fundamental issues about how molecular level processes control macroscopic properties and how behavior changes as dimensions approach the atomic scale. These issues are relevant to many processes and materials systems. The research will also serve as a testing ground for new hybrid techniques that couple very different descriptions of matter. The resulting atomistic/continuum algorithms are expected to be widely applicable to many other problems and systems with a wide range of length and time scales. Progress in developing mesoscale and continuum models from molecular simulations is also likely to enable related work in other fields.Broader Impact: An improved understanding of spreading, deformation, adhesion and friction would have broad impact in coating of materials, processing of polymers, and the design and formulation of improved adhesives and structural materials. The project will contribute to the workforce by training students and a postdoc in a wide range of interdisciplinary modeling methods. A new course on multiscale modeling will be developed to expose students from engineering andscience departments to these and related techniques. Finally, outreach efforts will bring research results to a wider audience through the annual Physics Fair at Johns Hopkins and collaborations with local high school teachers and the Maryland Science Center.

技术解释 这项研究涉及影响许多技术的基本非平衡过程：扩散，塑性变形，粘合失效和摩擦。传统的工程方法，这些现象开始从宏观连续方程的唯象本构关系和边界条件的有效性是值得怀疑的，特别是作为尺寸接近分子尺度。分子模拟将用于测试现有的连续描述，提供分子相互作用和宏观行为之间的联系，开发新的中尺度模型，并为无法从实验中获得的宏观模型提供输入。 扩散的模拟将研究预测存在于流体界面与固体相交的接触线附近的奇异应力。已经提出了几种竞争机制来消除奇异性，并且很难使用实验来区分它们。分子动力学和混合原子/连续方法将用于测试基于扩散和界面张力变化的新理论。研究结果将使更大的长度和时间尺度的中尺度模式的建设。这些将应用于更复杂几何形状的动力学，以研究接触角滞后和多孔介质中的多相流。 变形，粘附和摩擦的研究将集中在无定形聚合物玻璃，这是许多粘合剂和结构材料的主要成分。分子的连接性导致缠结，从而显著改变机械性能，特别是在大应变下。一种新的方法将被用来可视化缠结和相关的银纹形成和剪切变形过程中的应力/应变曲线的演变。原子和混合原子/连续模拟将被用来研究大块和薄膜的断裂能和机制。将研究不同的聚合物，以确定分子相互作用的哪些方面选择失效模式。摩擦工作将探讨本构关系的摩擦和体积变形之间的关系，纳米尺度和宏观摩擦系数的一些聚合物之间的对比，以及摩擦表面附近的分子排列的效果。智力优点：拟议的研究解决有关分子水平的过程如何控制宏观性能和行为如何变化的基本问题尺寸接近原子尺度。这些问题与许多工艺和材料系统有关。这项研究也将成为新的混合技术的试验场，这些技术将对物质的不同描述结合起来。由此产生的原子/连续体算法，预计将广泛适用于许多其他问题和系统的长度和时间尺度范围很广。从分子模拟发展中尺度和连续介质模型的进展也可能使其他领域的相关工作成为可能。更广泛的影响：对扩散、变形、粘附和摩擦的更好理解将对材料涂层、聚合物加工以及改进粘合剂和结构材料的设计和配方产生广泛影响。该项目将有助于通过培训学生和博士后在广泛的跨学科建模方法的劳动力。将开发一门关于多尺度建模的新课程，使工程和科学系的学生接触这些和相关技术。最后，外联工作将通过约翰霍普金斯的年度物理博览会以及与当地高中教师和马里兰州科学中心的合作，将研究成果带给更广泛的受众。