Self-concentrations and effective glass transition temperatures in polymer blends
Self-concentrations and effective glass transition temperatures in polymer blends
复制标题
DOI：
10.1021/ma9921706
复制
发表时间：
2000-07-11
期刊：
影响因子：
5.5
通讯作者：
McLeish, TCB
中科院分区：
文献类型：
--
作者：
Lodge, TP;McLeish, TCB
在可混溶的聚合物共混物中，A型单体的局部环境与本体组合物相比平均而言将富含A，对于B也是如此;这是链连接性的直接结果。因此，两个链的局部动力学可能表现出不同的温度和整体组成的依赖性。通过将长度尺度（或体积）分配给特定的动态模式，可以估计相关的“自集中”phi（s）。例如，我们将链的库恩长度l（K）与单体摩擦系数zeta联系起来，因此zeta的组成和温度依赖性应该受到对于类似于l（K）的体积V计算的phi（s）的影响（3）。然后，可以从phi（s）和phi计算有效局部组成phi（eff）。由于较低的T-g聚合物通常更柔韧，因此相关的phi（s）更大，并且混合物中的局部动力学可能与纯材料非常相似。另一方面，较高的T-g组分可具有较小的phi（s），因此其在混合物中的动力学将更能代表平均共混物组成。每种组分的有效玻璃化转变温度T-g（eff）可以由组成依赖的体积平均T-g估算为T-g（phi（eff））。这种分析提供了一个直接估计的差异，在明显的T-g的两个组分在混溶共混物，在合理的协议与文献中报道的四个不同的系统。此外，这种方法可以调和混溶共混动力学的其他功能，包括量热T-g的不对称加宽，混合的两个组件的链段松弛时间的不同影响，以及时间-温度叠加的失败。
In a miscible polymer blend the local environment of a monomer of type A will, on average, be rich in A compared to the bulk composition, phi, and similarly for B; this is a direct consequence of chain connectivity. As a result, the local dynamics of the two chains may exhibit different dependences on temperature and overall composition. By assigning a length scale (or volume) to particular dynamic mode, the relevant "self-concentration" phi(s) can be estimated. For example, we associate the Kuhn length of the chain, l(K), with the monomeric friction factor, zeta, and thus the composition and temperature dependences of zeta should be influenced by phi(s) calculated for a volume V similar to l(K)(3). An effective local composition, phi(eff), can then be calculated from phi(s) and phi. As lower T-g polymers are generally more flexible, the associated phi(s) is larger, and the local dynamics in the mixture may be quite similar to the pure material. The higher T-g component, on the other hand, may have a smaller phi(s), and thus its dynamics in the mixture would be more representative of the average blend composition. An effective glass transition temperature for each component, T-g(eff), can be estimated from the composition-dependent bulk average T-g as T-g(phi(eff)). This analysis provides a direct estimate of the difference in the apparent T-g's for the two components in miscible blends, in reasonable agreement with those reported in the literature for four different systems. Furthermore, this approach can reconcile other features of miscible blend dynamics, including the asymmetric broadening of the calorimetric T-g, the differing effects of blending on the segmental relaxation times of the two components, and the failure of time-temperature superposition.