Graham Michael, Shchukin Dmitry
Stephenson Institute for Renewable Energy, University of Liverpool, Peach Street, Liverpool L69 7ZF, U.K.
Langmuir. 2021 Jan 19;37(2):918-927. doi: 10.1021/acs.langmuir.0c03286. Epub 2021 Jan 6.
Core-shell structures containing active materials can be fabricated using almost infinite reactant combinations. A mechanism to describe their formation is therefore useful. In this work, nanoscale all-silica shell capsules with an aqueous core were fabricated by the HCl-catalyzed condensation of tetraethyl orthosilicate (TEOS), using Pickering emulsion templates. Pickering emulsions were fabricated using modified commercial silica (LUDOX TMA) nanoparticles as stabilizers. By following the reaction over a 24 h period, a general mechanism for their formation is suggested. The interfacial activity of the Pickering emulsifiers heavily influenced the final capsule products. Fully stable Pickering emulsion templates with interfacially active particles allowed a highly stable sub-micrometer (500-600 nm) core-shell structure to form. Unstable Pickering emulsions, i.e., where interfacially inactive silica nanoparticles do not adsorb effectively to the interface and produce only partially stable emulsion droplets, resulted in capsule diameter increasing markedly (1+ μm). Scanning electron microscope (SEM) and transmission electron microscope (TEM) measurements revealed the layered silica "colloidosome" structure: a thin yet robust inner silica shell with modified silica nanoparticles anchored to the outer interface. Varying the composition of emulsion phases also affected the size of capsule products, allowing size tuning of the capsules. Silica capsules are promising protective nanocarriers for hydrophilic active materials in applications such as heat storage, sensors, and drug delivery.
包含活性材料的核壳结构可以使用几乎无限的反应物组合来制造。因此，描述其形成的机制是有用的。在这项工作中，使用皮克林乳液模板，通过盐酸催化原硅酸四乙酯（TEOS）的缩合反应，制备了具有水相内核的纳米级全硅壳胶囊。使用改性的商业二氧化硅（LUDOX TMA）纳米颗粒作为稳定剂制备皮克林乳液。通过跟踪24小时内的反应，提出了其形成的一般机制。皮克林乳化剂的界面活性对最终的胶囊产品有很大影响。具有界面活性颗粒的完全稳定的皮克林乳液模板允许形成高度稳定的亚微米（500 - 600 nm）核壳结构。不稳定的皮克林乳液，即界面无活性的二氧化硅纳米颗粒不能有效吸附到界面上，仅产生部分稳定的乳液滴，导致胶囊直径显著增加（大于1μm）。扫描电子显微镜（SEM）和透射电子显微镜（TEM）测量揭示了层状二氧化硅“胶体囊泡”结构：一个薄而坚固的内部二氧化硅壳，改性二氧化硅纳米颗粒锚定在外界面上。改变乳液相的组成也会影响胶囊产品的尺寸，从而实现对胶囊尺寸的调节。二氧化硅胶囊在诸如蓄热、传感器和药物递送等应用中，有望成为亲水性活性材料的保护性纳米载体。
