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

聚合物混合物的相分离在平移不变性和旋转不变性条件下得到了广泛的研究。因此，相分离在时间和空间上是均匀和各向同性的。在对称破断条件下，利用光强分布诱导二苯乙烯标记聚苯乙烯（PSS）和聚乙烯醇甲基醚（PVME）混合物的相分离。在打破浓度波动平动不变性的实验中，采用具有明确强度梯度的紫外光诱导相分离。各向异性形态出现，优先取向几乎垂直于极化方向(E)。另一方面，利用线偏振光利用二苯乙烯的偏振选择性光异构作用来抑制相分离的旋转不变性。在第一类实验中，光强梯度引起的形貌只沿垂直于梯度的方向发展。强度梯度上游的相分离过程的动力学与均匀强度的情况几乎相似。另一方面，随着辐照时间的延长，下游流的相分离发展得更快。沿梯度观察到的相分离动力学是由梯度的大小决定的，似乎是普遍的，与光强无关。在第二种实验中，使用线偏振光产生光强的方向分布。相分离取决于，相对于偏振光方向E的相对方向。我们发现，在这种特殊情况下，相分离在E方向上进行得最快，而在垂直方向上则非常缓慢。结合之前使用温度梯度实验获得的数据（physics D 84,23,1995），本研究的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。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