Propagating Waves of Self-Assembly in Organosilane Monolayers

0853667 Genzer该项目的主要目标是详细了解小有机硅烷（OS）前体的组装和动力学，这些前体以定向方式从气相沉积到平坦的固体二氧化硅基底上，从而导致OS分子自发地前沿自组装成自组装单分子层（SAM）。 PI最近报道[Proc. Nat. Acad. sci. USA 104，10324（2007）]，这些OS吸附层从衬底边缘组织为具有明确定义的速度和形状的传播波前。 PI建议探索传播波前的分子性质（即，分子浓度和取向、面内重排、包括波动效应）作为气相的限制程度和OS分子的化学性质以及两个反向传播OS前沿如何相互作用的函数而改变。 PI还计划在将其纳入SAM之前解决OS在气相和衬底上的分子组装。 详细探索后一种现象将更好地理解在特定测量中发展的控制反应扩散波类（推与拉）的非线性项的性质。 智力优势：与反应扩散和自组装过程相关的波前在自然界中无处不在。 例如，传播前沿出现在结晶和其他不同的热力学有序过程。 在生物学中，繁殖前沿影响细胞运动和分裂，以及在更大规模的动物竞争性社会互动和种群动态中。 虽然它经常声称，自我维持或自催化的前传播是很好地描述了平均场反应扩散或相场排序模型，最近的模拟和理论论证表明，在较低的空间维度的波动效应可能会导致明显偏离经典的平均场理论的这种类型的前传播。 虽然这些观察结果对生物或材料加工环境中限制条件下发生的各种类型的有序前沿有重要意义，但对这一过程的分子方面知之甚少。 该计划是进行一系列全面的实验，旨在提供一些缺失的链接，使用模型系统的基础上定向自组装的OS表面上的图片，从而提供有价值的见解，可能适用于任何自催化前传播过程。 更广泛的影响：人类和其他生物的许多分子过程以及种群动态可以用经历随机局部位移事件的基本实体来描述。 当参与的实体集体从某种不稳定的状态移动到一个相对稳定的状态，具有更大的能量或竞争优势时，这些实体在大尺度上表现出规则的运动和相关的模式形成。 这些模式形成过程在自然界中无处不在，并在很大程度上控制着进化发展的连续波。 由于自催化波的传播是一种普遍现象，因此被设想用于描述它们的建模和类比可以应用于其他日常侵入性现象（例如，将外来植物物种引入新的环境，引发了一波又一波的郊区入侵生长。城市蔓延的增长、前沿聚合、金属膜的腐蚀、聚合物溶解以及许多其他因素）。 波动效应往往使这些前沿在时间上越来越不连贯（扩散），因此预计将极大地影响在物种（或不同类型的排序）竞争优势的条件下前沿模式之间的相互作用。 事实上，两个反向传播的自催化波前的相互作用是我们计划在这项工作中研究的关键领域之一。 除了拟议活动的科学方面外，还将在科学和技术方面开展活动，以了解许多相关的自然现象。

0853667GenzerThe principal goal of this project is to gain detailed understanding of the assembly and dynamics of small organosilane (OS) precursors deposited from the vapor phase in a directional manner onto flat solid silica substrates, which results in the spontaneous frontal self-assembly of OS molecules into self-assembled monolayers (SAM). The PIs have recently reported [Proc. Nat. Acad. Sci. USA 104, 10324 (2007)] that these OS adlayers organize from the substrate edge as propagating wave-fronts having well defined velocities and shapes. The PIs propose to explore how molecular nature of the propagating wave-fronts (i.e., molecular concentration and orientation, in-plane rearrangement, including fluctuation effects) changes as a function of the degree of confinement of the vapor phase and chemical nature of the OS molecules, as well as how two counter propagating OS fronts interact. The PIs also plan to address the molecular assembly of OS in the vapor phase and on the substrate before they are incorporated into the SAM. Exploring this latter phenomenon in detail will provide a better understanding of the nature of the non-linearity term governing the class of reaction diffusion waves (pushed versus pulled) that develop in a particular measurement. Intellectual Merit: Wave fronts associated with reaction diffusion and self-assembly processes are ubiquitous in the natural world. For instance, propagating fronts arise in crystallization and diverse other thermodynamic ordering processes. In biology, propagating fronts influence cell movement and division, as well as in the competitive social interactions and population dynamics of animals at much larger scales. While it is often claimed that self sustaining or autocatalytic front propagation is well described by mean-field reaction diffusion or phase field ordering models, recent simulations and theoretical arguments show that fluctuation effects in lower spatial dimensions can lead to appreciable deviations from the classical mean field theory of this type of front propagation. While these observations have significant implications for diverse types of ordering fronts that occur under confinement conditions in biological or materials processing contexts, not much is known about the molecular aspects of this process. The plan is to carry out a comprehensive series of experiments aimed at providing some missing links to the picture using a model system based on directional self-assembly of OS on surfaces, thus offering valuable insights that may be applicable to any autocatalytic front propagation process. Broader Impact: Many molecular processes as well as the population dynamics of humans and other organisms can be described in terms of fundamental entities undergoing random local displacement events. These exhibit regular motion at large scales and associated pattern formation as the participating entities collectively move from some unstable situation to a relatively stable state of greater energetic or competitive advantage. These pattern formation processes are ubiquitous in the natural world and largely govern successive waves of evolutionary development. Since the spreading of autocatalytic waves is a pervasive phenomenon, modeling and analogies conceived to describe them can be applied to other everyday invasive phenomena (e.g., the introduction of foreign plant species into new environments, triggering waves of invasive growth in the countryside,. the growth of urban sprawl, frontal polymerization, corrosion of metallic films, polymer dissolution, and many others). Fluctuation effects tend to make these fronts increasingly incoherent (diffuse) in time, and thus are expected to greatly impact the interactions between frontal patterns under conditions where species (or different types of ordering) compete for supremacy. Indeed, the interaction of two counter propagating autocatalytic wave fronts is one of the key areas we plan to study in this work. In addition to the scientific aspect of the proposed activities in understand a host of related natural phenomena.