Microphase separation in star block copolymers of styrene and isoprene. Theory, experiment, and simulation
Microphase separation in star block copolymers of styrene and isoprene. Theory, experiment, and simulation
复制标题
DOI：
10.1021/ma951762v
复制
发表时间：
1996-05-20
期刊：
影响因子：
5.5
通讯作者：
Erukhimovich, I
中科院分区：
文献类型：
--
作者：
Floudas, G;Pispas, S;Erukhimovich, I
用流变学和小角X射线散射法研究了苯乙烯（冠）和异戊二烯（核）四臂星星型两嵌段共聚物熔体的有序-无序转变（ODT）和有序化动力学。结果与相应的线性二嵌段进行了比较，并表明转变的方向由理论预测。平均场结构因子用于描述在T远大于T-ODT时的SAXS轮廓，并提取相互作用参数（chi）（T）的温度依赖性。由于（chi）的弱T依赖性，我们只能探索相图的一个小区域，即，对于f（PS）= 0.25，16.5 < N-chi（0）< 14.6。微相分离态由次要组分（PS）的球形微区组成，其类似于bcc相，然而，不具有完全对称性。为了探索在更宽的T范围内的形态，我们使用等效链的计算机模拟的结果，对于f（PS）= 0.25，其提供以下连续相：六边形-类似于螺旋体的双连续结构-体心立方（bcc）-无序。一个稳定的回旋相位的存在，在有限的组成范围内，也预测的理论基础上计算的高次谐波。本文首次给出了四臂星星嵌段共聚物的涨落校正相图。有序动力学已被研究的流变学和显示出显着放缓的有序过程相比，对称和不对称的线性二嵌段作为一个结果的分子拓扑结构和受约束的流动性链。
The order-disorder transition (ODT) and the ordering kinetics have been studied in four-arm star diblock copolymer melts of styrene (corona) and isoprene (core) by rheology and SAXS. The results are compared with the corresponding linear diblock and show that the transition shifts in the direction predicted by theory. The mean-field structure factor is used to describe the SAXS profiles at T much greater than T-ODT and to extract the temperature dependence of the interaction parameter (chi)(T). Because of the weak T dependence of (chi), we can explore only a small region of the phase diagram, namely, 16.5 < N-chi(0) < 14.6, for f(PS) = 0.25. The microphase-separated state consists of spherical microdomains of the minor component(PS) which resembles a bcc phase, however, not with the full symmetry. To explore the morphology over a broader T range, we use the results of computer simulation on equivalent chains, which for f(PS) = 0.25 provide the following succession of phases: hexagonal - a bicontinuous structure which resembles the gyroid - body-centered cubic (bcc) - disordered. The existence of a stable gyroid phase-over a limited composition range-is also predicted by a theory based on a calculation of the higher harmonics. Fluctuation corrected phase diagrams for four-arm star block copolymers are presented here, for the first time. The ordering kinetics have been studied by rheology and show a dramatic slowing of the ordering process as compared to symmetric and asymmetric linear diblocks as a result of the molecular topology and constrained mobility of chains.