Surfactant Mobilization of Adsorbed Polymer and its Effect on the Severity of Co-Adsorption Hysteresis

项目摘要Tilton，r.，沃什伯恩，北卡罗来纳州；卡内基-梅隆大学；CTS-0625135智力优势。两个观察结果推动了拟议的研究：i)聚合物通常存在于固/液界面的持久滞后状态中，因此吸附程度和聚合物构象对吸附历史很敏感；ii)当聚合物在与聚合物结合但从固体表面排斥的表面活性剂存在的情况下吸附时，滞后迹象有时会增加，但有时会减少。主要目的是确定表面活性剂结合控制吸附聚合物的动力学的机制，从而确定它们采样不同构象的能力以及它们对滞后共吸附的敏感性。聚合物/表面活性剂共吸附研究的最新进展是，尽管文献中包含了越来越多的实验体系的研究，但还没有进行系统设计的实验研究来检验滞后共吸附的起源和控制的假设，也没有建立理论模型来解释这一现象。该项目将提供发展适当理论所需的系统设计的实验基准。虽然该提案的重点主要是实验研究，但将开发动力学蒙特卡罗模拟，并与数据的趋势进行比较。动力学MC模拟的重点是通过记录吸附层对溶液组成阶跃变化的响应动力学来模拟实验滞后测量。这项研究的基本假设是，结合的表面活性剂可以增溶和动员聚合物“串”段，从而减少滞后现象。为了接触和动员列车节段，表面活性剂必须克服固体表面的排斥能屏障。以下测量将在具有系统变化的聚合物/表面活性剂结合能和表面活性剂/表面排斥能的模型系统中进行：i)通过不同吸附途径从聚合物表面活性剂混合物中吸附的程度，ii)表面活性剂对被吸附的聚合物和从本体溶液进入的聚合物之间交换的程度和动力学的影响，以及iii)表面活性剂对被吸附的聚合物表面扩散系数的影响。该研究项目将广泛有益于工业复杂流体配方实践。聚合物和表面活性剂的混合自组装和共吸附对复杂流体的宏观性质具有强大的控制作用。它们存在于制药、陶瓷、油漆、油墨和其他先进涂料等材料的制造和应用中。聚合物/表面活性剂混合物施加强烈的耦合力，微调材料的性能，但不幸的是，这些材料特别难配制。滞后效应的普遍存在加剧了配方的困难，在滞后效应中，最终材料的性能对组分添加的顺序和混合条件很敏感。通过确定滞后共吸附的来源，该项目将使新的复杂流体配方方法成为可能，这些方法将导致一系列行业的产品和工艺得到改进。该项目包括大学、工业和K-12教育活动。PI将为一门新的高级胶体和表面表征大学课程开发一个椭偏仪测量表面活性剂吸附的实验室模块。作为工业短期课程胶体、界面和复杂流体表征的基本仪器方法的一部分，该实验室模块将与椭偏仪的理论、实践和解释一起提供简明的讲座。该团队将与卡内基梅隆大学的工程你的未来项目合作，该项目将把女高中生带到校园里进行一天的实践活动，展示日常生活中的工程。

Project AbstractTilton, r., Washburn,N; Carnegie-Mellon Univ.; CTS-0625135Intellectual Merit. Two observations motivate the proposed research: i) that polymers often reside in persistent hysteretic states at the solid/liquid interface whereby the extent of adsorption and the polymer conformation are sensitive to the adsorption history and ii) that the signs of hysteresis are sometimes increased, but sometimes decreased, when polymers adsorb in the presence of surfactants that bind to the polymer but are repelled from the solid surface. The primary objective is to determine the mechanism by which surfactant binding controls the dynamics of adsorbed polymers and thus their ability to sample different conformations and their susceptibility to hysteretic co-adsorption. The state-of-the-art in polymer/surfactant co-adsorption research is that although the literature contains studies of an increasing number of experimental systems, no systematically designed experimental study has been performed that tests any hypothesis for the origin and control of hysteretic co-adsorption, and no theoretical model has been developed to explain the phenomenon. The project will provide the systematically designed experimental benchmarks that are needed for the development of appropriate theory. While the emphasis of the proposal is mainly on the experimental studies, kinetic Monte Carlo simulations will be developed and compared to trends in the data. The particular focus of the kinetic MC simulations is to mimic experimental hysteresis measurements by recording the dynamics of adsorbed layer response to a step-change in solution composition. The hypothesis underlying the proposed research is that bound surfactants solubilize and mobilize polymer "train" segments, thereby decreasing hysteresis. In order to access and mobilize train segments, surfactants must surmount the repulsive energy barrier from the solid surface. The following measurements will be made in model systems with systematically varying polymer/surfactant binding energies and surfactant/surface repulsive energies: i) extent of adsorption from polymer surfactant mixtures via different adsorption pathways, ii) surfactant influence on the extent and kinetics of exchange between adsorbed polymers and polymers entering from the bulk solution, and iii) surfactant influence on adsorbed polymer surface diffusion coefficients.Broader Impact. The research project will broadly benefit industrial complex fluid formulation practices. Mixed self-assembly and co-adsorption of polymers and surfactants exert powerful controls over the macroscopic properties of complex fluids. These are found in the manufacture and application of materials such as pharmaceuticals, ceramics, paints, inks, and other advanced coatings. Polymer /surfactant mixtures exert strongly coupled forces that fine tune material properties, but with the unfortunate consequence that these materials are particularly difficult to formulate. Formulation difficulties are exacerbated by the prevalence of hysteresis effects, where the final material properties are sensitive to the order of component addition and mixing conditions. By determining the origins of hysteretic co-adsorption, this project will enable new complex fluid formulation methods that will lead to improved products and processes over a spectrum of industries. The project includes university, industrial, and K-12 educational activities. The PI will develop a laboratory module on Ellipsometric Measurement of Surfactant Adsorption" for a new Advanced Colloid and Surface Characterization university course. A concise lecture on theory, practice, and interpretation of ellipsometry will be offered together with the lab module as part of the industrial short course Essential Instrumental Methods for Colloid, Interface, and Complex Fluid Characterization. The team will collaborate with Carnegie Mellon's Engineering Your Future program that brings female high school students onto campus for a day of hands-on activities illustrating engineering in everyday life.