Department of Physics, Soft Matter at Interfaces , Technical University Darmstadt , Alarich-Weiss-Straße 10 , 64287 Darmstadt , Germany.
Institute of Physical Chemistry , University Hamburg , Grindelallee 117 , 20146 Hamburg , Germany.
J Phys Chem B. 2019 Mar 14;123(10):2405-2413. doi: 10.1021/acs.jpcb.8b09236. Epub 2019 Mar 4.
The aim of this study is to tailor the inner structure of positively charged poly-( N-isopropylacrylamid- co-allylamine) (P(NIPAM- co-AA)) microgels for a better control of the distribution of negatively charged magnetic cobaltferrite (CoFeO@CA) nanoparticles (MNPs) within the microgels. Therefore, two different strategies are followed for the microgel synthesis: the (one pot) batch method which leads to a higher cross-linker density in the microgel core and the feeding method which compensates different reaction kinetics of the cross-linker and the monomers. The latter one is expected to result in a homogeneous cross-linker distribution. Information about the cross-linker distribution is indirectly gained by measuring the elastic modulus via indentation experiments with an atomic force microscope. While the batch method results in a higher elastic modulus in the center of the microgel indicating a core/shell structure, the feeding method leads to a constant elastic modulus over the whole microgel. The loading with MNPs and their distribution are studied with transmission electron microscopy (TEM). The TEM images show a large difference in the MNP distribution which is correlated to the cross-linker distribution of both types of microgels. The batch method microgel has a low MNP concentration in the core. The feeding method microgel shows a much more homogeneous distribution of MNPs across the microgel. The latter one also shows a stronger charge reversal which is a hint for a higher loading of the feeding method microgel. Dynamic light scattering and electrophoretic mobility measurements demonstrate that for both types of microgels, the temperature sensitivity is preserved after loading with MNPs.
本研究旨在调整带正电荷的聚（N-异丙基丙烯酰胺-co-丙烯酰胺）（P（NIPAM-co-AA））微凝胶的内部结构，以更好地控制带负电荷的磁性钴铁氧体（CoFeO@CA）纳米颗粒（MNPs）在微凝胶内的分布。因此，采用了两种不同的微凝胶合成策略：一锅批处理法，该方法导致微凝胶核中的交联剂密度更高；进料法，该方法补偿了交联剂和单体的不同反应动力学。后一种方法有望导致交联剂的均匀分布。通过原子力显微镜的压痕实验间接测量弹性模量来获得有关交联剂分布的信息。虽然批处理法导致微凝胶中心的弹性模量更高，表明存在核/壳结构，但进料法导致整个微凝胶的弹性模量保持不变。通过透射电子显微镜（TEM）研究了 MNPs 的负载及其分布。TEM 图像显示了 MNP 分布的巨大差异，这与两种类型的微凝胶的交联剂分布相关。批处理法微凝胶在核中具有较低的 MNPs 浓度。进料法微凝胶显示出 MNPs 在整个微凝胶中更均匀的分布。后一种方法还显示出更强的电荷反转，这表明进料法微凝胶的负载更高。动态光散射和电泳迁移率测量表明，对于两种类型的微凝胶，在负载 MNPs 后，其温度敏感性得以保留。
