Brewster angle optical reflection observation of self-limiting nanoparticle monolayer self-assembly at a liquid/liquid interface

Real-time optical reflection of incident p-polarized light near Brewster’s angle shows that after drop-casting iron oxide nanoparticles (NPs) in heptane on top of a diethylene glycol (DEG) liquid substrate, an iron oxide NP layer forms at the DEG/heptane interface, and it self-limits to a monolayer even when there are excess NPs dispersed in the upper heptane phase. Most modes of NP self-assembly do not self-limit growth after the formation of a single monolayer. Observations are compared to a reflection model incorporating the reflectances expected at each interface. An effective medium model of the dielectric constant is used to model the reflectance of the NP layer at the DEG/heptane interface.

入射p偏振光在布儒斯特角（Brewster’s angle）附近的实时光学反射实验表明：将分散于正庚烷中的氧化铁纳米颗粒（NPs）通过滴涂法（drop-casting）沉积于二甘醇（DEG）液体基底表面后，会在DEG/正庚烷界面处形成氧化铁纳米颗粒层；即便上层正庚烷相内存在过量分散的纳米颗粒，该颗粒层仍会自限性地仅形成单层膜。当前多数纳米颗粒自组装模式在形成单分子层后，无法实现生长自限。本观测结果与结合各界面预期反射率的反射模型进行了对比，同时采用介电常数有效介质模型，对DEG/正庚烷界面处纳米颗粒层的反射率开展了建模分析。