The Critical Role of Glass Transition Phenomena on the Dynamics of Miscible Polymer Blends

9977928Kumar在玻璃形成液体中的分子间摩擦知之甚少--这一事实在两种聚合物的可混溶混合物中得到了强烈的证明。随着共混物组成在恒定的T-Tg下变化，两个单体之间的有效摩擦系数可以非单调的方式在几个数量级上变化。浓度波动模型似乎为理解这种现象提供了一个很有前途的框架，并已通过实验进行了测试。对两种模型聚烯烃共混体系进行了综合研究，并进行了实验验证。用一套实验探头对两种模型聚烯烃共混体系进行了全面的研究。这将描绘出所有相关长度尺度上的动力学，从单体的分段运动到整个链的运动。选择这些混合物是为了以系统的方式改变浓度波动，并将作为混合动力学非常需要的数据库。有关分段动力学的信息将用于检验和改进用于局部动力学的电流浓度波动模型。链动力学数据将允许对该模型在链水平上的拟议扩展进行测试，从而能够预测分子间摩擦，从而预测可混溶混合物的粘度和扩散系数。目前模型中最不被理解的部分是协同重排区域的概念，它指的是空间中所有单体都必须协同运动以放松压力的区域。因此，分子模拟将被用来理解合作运动，这对于理解聚合物混合物中的动力学至关重要，也对所有玻璃形成液体中的动力学至关重要。这一建议的目的是构建一个链动力学预测模型，该模型将在浓度波动和有效分子间摩擦之间建立联系。这不仅将导致聚合物工业所需的可混溶聚合物混合物的粘度的预测模型，而且对于了解所有玻璃形成液体的动力学也具有深远的影响。聚合物混合物被用于越来越多的消费品，包括运输行业中的金属替代品，它能够在不牺牲强度的情况下减轻重量，从而在运输中使用更少的燃料。聚合物混合物对于塑料回收也是至关重要的。提出的研究将极大地扩展我们对这些复杂材料的理解。

9977928KumarIntermolecular friction in glass-forming liquids is poorly understood - a fact that is strongly demonstrated in miscible mixtures of two polymers. The effective friction coefficient between two monomers can vary over several orders of magnitude in a nonmonotonic fashion as blend composition is changed at constant T - Tg. A concentration fluctuation model appears to offer a promising framework for understanding such phenomena, and has been tested with experiments. A comprehensive study of two model polyolefin blend systems, tested with experiments. A comprehensive study of two model polyolefin blend systems, using a suite of experimental probes, is proposed here. This will delineate the dynamics at all relevant length scales, from the segmental motion of monomers to the motion of entire chains. These blends are chosen to vary concentration fluctuation in a systematic manner, and will serve as a greatly needed database for blend dynamics. Information on segmental dynamics will be used to test and improve the current concentration fluctuation model for local dynamics. Chain dynamics data will allow testing of proposed extensions of this model to the chain level, enabling prediction of intermolecular friction, and thus the viscosity and diffusion coefficients of miscible blends. The least-understood part of the current model is the notion of a cooperatively rearranging region, which refers to a region in space where all monomers have to move cooperatively to relax stress. Thus, molecular simulations will be utilized to understand cooperative motion, crucial for understanding dynamics in polymer blends, and also in all glass-forming liquids. The goal of this proposal is to construct a predictive model for chain dynamics, which will make the connection between concentration fluctuations and effective intermolecular friction. This will not only result in a predictive model for the viscosity of miscible polymer blends, needed in the polymers industry, but also have far-reaching consequences for understanding the dynamics of all glass-forming liquids.Polymer blends are used in an increasing number of consumer products, including metals replacement in the transportation industry that enables weight to be reduced without sacrificing strength, thereby using less fuel in transportation. Polymer blends are also vital for plastics recycling. The proposed research will greatly expand our understanding of these complicated materials.