Spinodal dewetting of liquid-liquid thin-films

The spinodal dewetting of a thin liquid polystyrene (PS) film from a liquid polymethylmethacrylate (PMMA) substrate is investigated experimentally and theoretically. Comparing experimental results of the evolving PS-air and PS-PMMA interfaces with the predictions from linear stability analysis shows that both spinodal wavelength and rupture times deviate unexpectedly. The key factor for this discrepancy is the altered mode selection process due to the initial surface roughness of the liquid-air and liquid-liquid interfaces perturbed by partially correlated colored noise in the linearly unstable region. The strong impact of noise on the mode selection and on the rupture time is clearly demonstrated through long-time numerical solutions of the full nonlinear model when compared to experimental results. This strong impact of noise is relevant only for liquid bilayers, and not for spinodal dewetting on solids, due to the presence of two moving interfaces and calls for new strategies to incorporate also thermal fluctuations into the modelling of those systems.

本研究通过实验与理论结合的方法，对液态聚苯乙烯（PS）薄膜在液态聚甲基丙烯酸甲酯（PMMA）基底上发生的旋节线去湿（spinodal dewetting）现象进行了探究。将演化过程中PS-空气界面与PS-PMMA界面的实验结果，与线性稳定性分析（linear stability analysis）的预测结果进行比对后发现，旋节波长与破裂时间均出现了非预期的偏差。造成这一偏差的核心诱因是，线性不稳定区域内部分相关有色噪声（colored noise）扰动了液-气与液-液界面的初始表面粗糙度，进而改变了模式选择过程。通过完整非线性模型（nonlinear model）的长时间数值求解结果与实验数据的对比，我们清晰地验证了噪声对模式选择与破裂时间的显著影响。由于存在两个动态演化的界面，噪声的这一显著影响仅适用于液态双层膜（liquid bilayers）体系，而不适用于固体基底上的旋节线去湿现象；这一发现也要求我们开发新的建模策略，将热涨落（thermal fluctuations）也纳入这类体系的建模框架中。