Structure and Viscoelastic Properties of Diblock Copolymers in Disordered State

本文研究了聚苯乙烯-b-2-乙烯基吡啶及其稀化产物在有序-无序过渡（ODT）附近无序状态下的结构和粘弹性。该试样适合于此类研究，因为两种组分具有几乎相同的物理性质，但在某些条件下仍会分离。我们取得的成果如下：(1)通过流变学和小角中子散射（SANS）测量，我们确定了嵌段共聚物样品在宽分子量（10k至百万）和浓度（10%至散装）范围内的ODT。半稀释区的数据可以用考虑波动效应的理论来解释。然而，半稀区和浓区之间的过渡并不明显。(2)动态力学分析得到的弹性参数比构件的弹性参数大几倍，而稳定剪切流测得的弹性参数与构件的弹性参数几乎相同。这种差异不能仅仅用流变行为来解释。有两种可能；一种是流动诱导的有序，另一种是稳定剪切流对波动的抑制。(3)为了澄清上述行为，我们在相应条件下进行了flow- sans测量，发现没有流动诱导的微畴结构，因此我们认为上述粘弹性行为可以用稳定剪切流动下的波动效应及其抑制来解释。

We have studied structure and viscoelastic properties of poly(styrene-b-2-vinyl-pyridine)s and their deutrated counterparts in the disordered state near the order-disorder transition (ODT) both in bulk and in a common good solvent. This specimen is suitable for such study since both components have almost the same physical properties but still segregate at certain conditions. The results we have achieved are listed as follows.(1)We determined ODT for the block copolymer samples in wide ranges of molecular weight (10k to million) and concentration (10% up to bulk) by rheometry and small angle neutron scattering (SANS) measurements. The data in semidilute region could be explained by the theory which account for fluctuation effect. However, the transition between semidilute and concentrated regions was not clear.(2)We found that the elastic parameters obtained by dynamic mechanical analysis are a few times larger than those of components but the elastic parameters measured by steady shear flow become almost the same as those of components. The difference cannot be explained by rheological behavior alone. There are two possibilities ; one is flow-induced ordering and another is suppression of fluctuation by steady shear flow.(3)To clarify above behavior, we performed flow-SANS measurements at the corresponding condition and found that there is no flow-induced microdomain structure so that we concluded the above viscoelastic behavior can be explained by fluctuation effect and its suppression under steady shear flow.