聚 4-乙烯基吡啶/聚苯乙烯双层膜中去湿和层反转的相互作用。

School of Chemistry F11, The University of Sydney, NSW 2006, Australia.

Langmuir. 2010 Oct 19;26(20):15989-99. doi: 10.1021/la103078k.

We investigated the morphology and dynamics of the dewetting of metastable poly(4-vinylpyridine) (P4VP) thin films situated on top of polystyrene (PS) thin films as a function of the molecular weight and thickness of both films. We focused on the competition between the dewetting process, occurring as a result of unfavorable intermolecular interactions at the P4VP/PS interface, and layer inversion due to the lower surface energy of PS. By means of optical and atomic force microscopy (AFM), we observed how both the dynamics of the instability and the morphology of the emerging patterns depend on the ratio of the molecular weights of the polymer films. When the bottom PS layer was less viscous than the top P4VP layer (liquid-liquid dewetting), nucleated holes in the P4VP film typically stopped growing at long annealing times because of a combination of viscous dissipation in the bottom layer and partial layer inversion. Full layer inversion was achieved when the viscosity of the top P4VP layer was significantly greater (>10⁴) than the viscosity of the PS layer underneath, which is attributed to strongly different mobilities of the two layers. The density of holes produced by nucleation dewetting was observed for the first time to depend on the thickness of the top film as well as the polymer molecular weight. The final (completely dewetted) morphology of isolated droplets could be achieved only if the time frame of layer inversion was significantly slower than that of dewetting, which was characteristic of high-viscosity PS underlayers that allowed dewetting to fall into a liquid-solid regime. Assuming a simple reptation model for layer inversion occurring at the dewetting front, the observed surface morphologies could be predicted on the basis of the relative rates of dewetting and layer inversion.

我们研究了位于聚苯乙烯（PS）薄膜上的亚稳聚 4-乙烯基吡啶（P4VP）薄膜的去湿形态和动力学，这取决于两种薄膜的分子量和厚度。我们专注于去湿过程的竞争，这是由于 P4VP/PS 界面上不利的分子间相互作用而发生的，以及由于 PS 的低表面能而导致的层反转。通过光学和原子力显微镜（AFM），我们观察到不稳定的动力学和出现的图案的形态如何取决于聚合物膜的分子量比。当底层 PS 层比顶层 P4VP 层粘性小（液-液去湿）时，由于底层的粘性耗散和部分层反转的综合作用，P4VP 膜中的核化孔通常在长时间退火后停止生长。当顶层 P4VP 层的粘度明显大于底层 PS 层的粘度（>10⁴）时，完全实现了层反转，这归因于两层之间具有非常不同的迁移率。首次观察到核化去湿产生的孔密度不仅取决于顶层膜的厚度，还取决于聚合物分子量。只有当层反转的时间框架明显慢于去湿的时间框架时，才能实现孤立液滴的最终（完全去湿）形态，这是高粘度 PS 底层的特征，允许去湿落入液-固状态。假设层反转在去湿前沿发生的简单爬行模型，根据去湿和层反转的相对速率，可以预测观察到的表面形态。