Mechanism of Phase Separation of Polymar Blends Induced by a Gradient of Light Intersity

在平移和转动不变的条件下，聚合物混合物的相分离已被广泛地研究。因此，相分离在时间和空间上均匀而各向同性地进行。在对称破缺条件下，利用光强分布研究了二苯乙烯标记聚苯乙烯(PSS)和聚乙烯基甲基醚(PVME)混合物的相分离。在浓度涨落的平移不变性被打破的实验中，使用具有明确强度梯度的紫外光来诱导相分离。出现了各向异性的形貌，择优取向几乎垂直于极化方向(E)。另一方面，利用二苯乙烯类化合物的偏振选择性光致异构化作用，利用线偏振光来抑制相分离的旋转不变性。在第一类实验中，Gra-…诱导的形貌更适中的光强度倾向于完全沿着垂直于渐变的方向发展。强度梯度上游的相分离动力学过程与均匀强度的情况几乎相似。另一方面，下游的相分离随着辐照时间的延长而演化得更快。沿梯度观察到的相分离动力学由梯度的大小决定，似乎是普遍的，与光强度无关。在第二类实验中，线偏振光被用来产生光强的取向分布。现在，相分离取决于相对于偏振光方向E的相对取向。研究发现，在这种情况下，相分离沿E方向进行得最快，而在垂直方向上则变得非常缓慢。结合以前使用温度梯度(Physica D 84，23,1995)获得的数据，本研究结果为设计具有可控梯度结构的聚合物提供了一种新的有效方法。较少

Phase separation of polymer mixtures has been extensively studied under conditions of translational and rotational invariance. As a consequence, phase separation proceeds homogeneously and isotropically with time and space. In this study, phase separation of a mixture composed of stilbene-labeled polystyrene (PSS) and poly (vinyl methyl ether)(PVME) was induced under symmetry-breaking conditions by using a distribution of light intensity. In the experiments where the translational invariance of concentration fluctuations was broken, uv light with a well-defined intensity gradient was used to induce the phase separation. Anisotropic morphology emerge with the preferred orientation almost perpendicular to the polarization direction (E). On the other hand, linearly polarized light was used to brake the rotational invariance of phase separation by taking advantages of the polarization-selective photoisomerization of stilbene.In the first kind of experiments, the morphology induced by a gra … More dient of light intensity tends to develop exclusively along the direction perpendicular to the gradient. The phase separation in the upper stream of the intensity gradient proceeds with the kinetics almost similar to the case of using homogeneous intensity. On the ther hand, phase separation in the lower stream evolves much faster with irradiation time. The phase separation kinetics observed along the gradient is determined by the magnitude of the gradient and seems to be universal and independent from the light intensity.In the second kind of experiments, linearly polarized light was used to produce an orientation distribution of the light intensity. The phase separation depends, now, on the relative orientation with respect to the direction E of the polarized light. It was found, in this particular case, that the phase separation proceeds fastest along the direction of E, whereas it becomes very slow along the perpendicular direction.Combined with the data obtained previously with experiments using a temperature gradient (Physica D 84, 23, 1995), the results obtained in this study suggest a new and efficient way to design polymers with controllable graded structures. Less