Saxena S, Cizmeciyan D, Kornfield J A
California Institute of Technology, Pasadena 91125, USA.
Solid State Nucl Magn Reson. 1998 Sep;12(2-3):165-81. doi: 10.1016/s0926-2040(98)00060-5.
Recent two-dimensional (2D) 2H-NMR studies on nearly ideal mixtures are reviewed. The use of selective deuterium labeling allows the unambiguous observation of the individual segmental dynamics of each component in the blend. 2D exchange spectra provide both the mean motional rates and the motional distributions, which was necessary to discriminate among the disparate explanations of blend behavior. The components exhibit very different mean mobilities and broad mobility distributions near the glass transition. The broad macroscopic glass transition in the blends is attributed to both these two kinds of dynamic heterogeneities. The individual mean motional rates are used to define distinct glass transition temperatures, T(g,i) for each species, i. The separation between the T(g,i),s of the two species increases with the content of the high-T(g) component. The widths of their individual motional distributions also increase with the content of the high-T(g) component. These two effects combine to produce the increase in both the anomalously broad glass transition and the thermorheological complexity of these blends with fraction of the high-T(g) component.
本文综述了近期对近理想混合物进行的二维（2D）2H-NMR研究。选择性氘标记的应用使得能够明确观察共混物中各组分的单个链段动力学。二维交换光谱提供了平均运动速率和运动分布，这对于区分共混行为的不同解释是必要的。在玻璃化转变附近，各组分表现出非常不同的平均迁移率和较宽的迁移率分布。共混物中宽泛的宏观玻璃化转变归因于这两种动力学不均匀性。利用单个平均运动速率为每种物质i定义了不同的玻璃化转变温度T(g,i)。两种物质的T(g,i)之间的间隔随高T(g)组分的含量增加而增大。它们各自运动分布的宽度也随高T(g)组分的含量增加而增大。这两种效应共同导致了这些共混物的异常宽泛的玻璃化转变和热流变复杂性随高T(g)组分比例的增加而增加。
