Saini Apurve, Theis-Bröhl Katharina, Koutsioubas Alexandros, Krycka Kathryn L, Borchers Julie A, Wolff Max
Department for Physics and Astronomy, Uppsala University, Uppsala, Sweden.
University of Applied Sciences, Bremerhaven, Germany.
Langmuir. 2021 Apr 13;37(14):4064-4071. doi: 10.1021/acs.langmuir.0c03235. Epub 2021 Apr 2.
We study the assembly of magnetite nanoparticles in water-based ferrofluids in wetting layers close to silicon substrates with different functionalization without and with an out-of-plane magnetic field. For particles of nominal sizes 5, 15, and 25 nm, we extract density profiles from neutron reflectivity measurements. We show that self-assembly is only promoted by a magnetic field if a seed layer is formed at the silicon substrate. Such a layer can be formed by chemisorption of activated -hydroxysuccinimide ester-coated nanoparticles at a (3-aminopropyl)triethoxysilane functionalized surface. Less dense packing is reported for physisorption of the same particles at a piranha-treated (strongly hydrophilic) silicon wafer, and no wetting layer is found for a self-assembled monolayer of octadecyltrichlorosilane (strongly hydrophobic) at the interface. We show that once the seed layer is formed and under an out-of-plane magnetic field further wetting layers assemble. These layers become denser with time, larger magnetic fields, higher particle concentrations, and larger moment of the nanoparticles.
我们研究了在有无面外磁场的情况下，不同功能化的硅基底附近的水基铁磁流体中磁铁矿纳米颗粒在润湿层中的组装情况。对于标称尺寸为5、15和25纳米的颗粒，我们从中子反射率测量中提取密度分布。我们表明，只有当在硅基底上形成种子层时，磁场才会促进自组装。这样的层可以通过在（3-氨丙基）三乙氧基硅烷功能化表面上化学吸附活化的羟基琥珀酰亚胺酯包覆的纳米颗粒来形成。对于相同颗粒在经硫酸和过氧化氢处理（强亲水性）的硅片上的物理吸附，报道的堆积密度较低，并且在界面处未发现十八烷基三氯硅烷（强疏水性）自组装单分子层的润湿层。我们表明，一旦形成种子层，在面外磁场作用下会进一步组装润湿层。随着时间的推移、磁场增大、颗粒浓度升高以及纳米颗粒的磁矩增大，这些层会变得更致密。
