Rastogi Vinayak, García Antonio A, Marquez Manuel, Velev Orlin D
Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905, USA.
Macromol Rapid Commun. 2010 Jan 18;31(2):190-5. doi: 10.1002/marc.200900587. Epub 2009 Dec 4.
We demonstrate how droplet templates dispensed on superhydrophobic substrates can be used to fabricate both shape-anisotropic ("doughnut") and composition-anisotropic ("patchy magnetic") supraparticles. The macroscopic shape of the closely-packed particle assemblies is guided by the droplet meniscus. Aqueous droplets of monodisperse microsphere suspensions dispensed on the substrates initially acquire near-spherical shape due to a high contact angle. During the solvent evaporation, however, silica suspension droplets undergo shape transitions (concaving) guiding the structure of the final assemblies into doughnut supraparticles. Composition anisotropy is achieved by drying a droplet containing a mixed suspension of latex and magnetic nanoparticles, while exposing it to magnetic field gradients. Depending on the pattern of the magnetic fields, the magnetic nanoparticles segregate into single, bilateral, or trilateral, patched spherical supraparticles. The physical effects leading to the development of anisotropy are discussed. Unlike the conventional wet self-assembly (WSA) methods where the final structures need to be extracted from the liquid environment, this efficient one-step procedure produces ready to use "dry" supraparticles.
我们展示了如何利用 dispensed 在超疏水基底上的液滴模板来制造形状各向异性（“甜甜圈”状）和成分各向异性（“补丁状磁性”）的超粒子。紧密堆积的粒子聚集体的宏观形状由液滴弯月面引导。dispensed 在基底上的单分散微球悬浮液的水滴最初由于高接触角而呈现近球形。然而，在溶剂蒸发过程中，二氧化硅悬浮液滴会发生形状转变（凹陷），将最终聚集体的结构引导成甜甜圈状超粒子。通过干燥含有乳胶和磁性纳米粒子混合悬浮液的液滴，同时将其暴露于磁场梯度中，可实现成分各向异性。根据磁场模式，磁性纳米粒子会分离成单个、双侧或三边的补丁状球形超粒子。讨论了导致各向异性发展的物理效应。与传统的湿自组装（WSA）方法不同，在传统方法中最终结构需要从液体环境中提取，这种高效的一步法可生产随时可用的“干燥”超粒子。
