Department of Chemistry, Stony Brook University, Stony Brook, NY, USA.
Center for Functionalized Nanomaterials, Brookhaven National Laboratory, Upton, NY, USA.
J Colloid Interface Sci. 2019 Mar 7;538:209-217. doi: 10.1016/j.jcis.2018.11.084. Epub 2018 Nov 23.
Stratification or self-segregation of multicomponent particle mixtures during drying is an important phenomenon to understand for the development of single-step deposition processes for complex coatings. We hypothesize that varying the ratio of particle Peclet numbers will lead to different types of stratification behavior.
Binary colloidal films of polystyrene and silica were prepared by evaporative film formation, and stratification of nanoparticles of different size ratio (7.7-1.2) was studied using microbeam small-angle X-ray scattering (SAXS).
SAXS spectra showed noticeable variations at different film depths, consistent with stratification. These results are quantified to obtain vertical composition profiles. We observe "sandwich"-type layered structures at different nanoparticle size ratios, which to our knowledge have not been previously observed experimentally or predicted by theory. For example, for films of larger particle size ratios (7.7-4.8), large particles are enriched at the film top and bottom, leading to a large-small-large or "LSL" behavior; while within films of smaller particle size ratio (2.2-1.2), small particles are enriched at the top and bottom of the film (small-large-small or "SLS" structures). The enrichment of particles at the top persists over several hundred particle layers and is not just a single monolayer pinned to the upper surface.
在干燥过程中多组分颗粒混合物的分层或自分离是理解复杂涂层的单步沉积工艺发展的重要现象。我们假设改变颗粒 Peclet 数的比值将导致不同类型的分层行为。
通过蒸发成膜制备聚苯乙烯和二氧化硅的二元胶体膜，并使用微束小角 X 射线散射（SAXS）研究不同粒径比（7.7-1.2）的纳米颗粒的分层。
SAXS 光谱在不同膜深处显示出明显的变化，与分层一致。这些结果经过量化处理以获得垂直的成分分布。我们观察到不同纳米颗粒粒径比的“三明治”层状结构，据我们所知，这些结构以前没有在实验中观察到或通过理论预测到。例如，对于粒径比较大的膜（7.7-4.8），大颗粒在膜的顶部和底部富集，导致大-小-大或“LSL”行为；而在粒径比较小的膜（2.2-1.2）中，小颗粒在膜的顶部和底部富集（小-大-小或“SLS”结构）。颗粒在顶部的富集持续数百个颗粒层，而不仅仅是单个单层被固定在上表面。
