Zwar Elena, Kemna Andre, Richter Lena, Degen Patrick, Rehage Heinz
Physikalische Chemie II, TU Dortmund, 44227 Dortmund, Germany.
J Phys Condens Matter. 2018 Feb 28;30(8):085101. doi: 10.1088/1361-648X/aaa6f5.
In this article we investigated the deformation of alginate capsules in magnetic fields. The sensitivity to magnetic forces was realised by encapsulating an oil in water emulsion, where the oil droplets contained dispersed magnetic nanoparticles. We solved calcium ions in the aqueous emulsion phase, which act as crosslinking compounds for forming thin layers of alginate membranes. This encapsulating technique allows the production of flexible capsules with an emulsion as the capsule core. It is important to mention that the magnetic nanoparticles were stable and dispersed throughout the complete process, which is an important difference to most magnetic alginate-based materials. In a series of experiments, we used spinning drop techniques, capsule squeezing experiments and interfacial shear rheology in order to determine the surface Young moduli, the surface Poisson ratios and the surface shear moduli of the magnetically sensitive alginate capsules. In additional experiments, we analysed the capsule deformation in magnetic fields. In spinning drop and capsule squeezing experiments, water droplets were pressed out of the capsules at elevated values of the mechanical load. This phenomenon might be used for the mechanically triggered release of water-soluble ingredients. After drying the emulsion-filled capsules, we produced capsules, which only contained a homogeneous oil phase with stable suspended magnetic nanoparticles (organic ferrofluid). In the dried state, the thin alginate membranes of these particles were rather rigid. These dehydrated capsules could be stored at ambient conditions for several months without changing their properties. After exposure to water, the alginate membranes rehydrated and became flexible and deformable again. During this swelling process, water diffused back in the capsule. This long-term stability and rehydration offers a great spectrum of different applications as sensors, soft actuators, artificial muscles or drug delivery systems.
在本文中，我们研究了藻酸盐胶囊在磁场中的变形情况。通过包裹水包油乳液来实现对磁力的敏感性，其中油滴中含有分散的磁性纳米颗粒。我们在水相乳液中溶解钙离子，钙离子作为交联化合物用于形成藻酸盐膜薄层。这种包封技术能够生产以乳液为胶囊核心的柔性胶囊。需要指出的是，磁性纳米颗粒在整个过程中保持稳定且分散，这与大多数基于藻酸盐的磁性材料有重要区别。在一系列实验中，我们使用旋转滴技术、胶囊挤压实验和界面剪切流变学来测定磁敏藻酸盐胶囊的表面杨氏模量、表面泊松比和表面剪切模量。在额外的实验中，我们分析了胶囊在磁场中的变形情况。在旋转滴和胶囊挤压实验中，在机械负荷升高时，水滴从胶囊中被挤出。这种现象可用于机械触发水溶性成分的释放。将填充乳液的胶囊干燥后，我们制备出仅包含均匀油相和稳定悬浮磁性纳米颗粒（有机铁磁流体）的胶囊。在干燥状态下，这些颗粒的藻酸盐薄膜相当坚硬。这些脱水胶囊可在环境条件下储存数月而不改变其性质。接触水后，藻酸盐膜重新水化，再次变得柔韧且可变形。在这个膨胀过程中，水扩散回胶囊中。这种长期稳定性和再水化特性为作为传感器、软致动器、人造肌肉或药物输送系统等提供了广泛的不同应用。
