Magnetically tunable surface properties of soft magnetoactive elastomers

在磁致弹性体（MAE）中，如果基质是软的，则可磁化填料（微米尺寸的填料颗粒的排列）的微观结构可以在外部磁场中显著改变。填料的这种重构在MAE样品的自由表面上是明显的，并且表面性质（例如润湿性或粘附性）的相应变化可用于广泛的应用，例如微流体装置或磁性可控细胞培养基底等中的液体操作。该项目的主要目标是研究磁场诱导的MAE材料表面变化（例如其形貌），并建立复合材料组成成分（即基质和填料，包括其界面）的物理化学性质与磁场中表面性质（例如润湿性或扩散反射）的变化之间的一般关系。表观宏观表面特征由复合材料表面附近的组成成分的微观性质决定，其系统地变化。通过这样做，应能够实现磁场响应MAE表面的预测设计。本项目的主要工作量将是系统和彻底的表征（各种表面显微镜方法，光学轮廓术，表面散射技术等）。磁致弹性体的磁场诱导表面变化的研究以及复合材料的表面性质与本体（磁流变和磁性能、填料的组成等）之间的相关性的测定。其组成成分的性质。基质为聚二甲基硅氧烷基。填料组合物将包含通过超细（纳米）和细磁性颗粒（例如尖晶石铁氧体）增强的可变尺寸和形态（球体、薄片）的微米尺寸的软磁（铁）和/或硬磁（NdFeB）颗粒。将调节颗粒的表面性质，例如用于增加它们的疏水性或功能化。实验结果将与最近的介观理论方法的结论进行比较，以验证其有效性，并确定其限制。为了强调结构-性质-功能关系，将在具有外部磁场控制的MAE材料的三个可能的应用领域的背景下进行测量：i）可调表面润湿，ii）可擦除和可重构衍射光学元件，以及iii）用于液晶的可调对准层。后一种应用将用于检测关闭外场后与表面相邻的层中微观填料的弛豫行为。将对材料性能进行长期观察，以得出有关功能表面性能老化/退化及其潜在物理化学机制的结论。

In magnetoactive elastomers (MAEs), the microstructure of the magnetizable filler (arrangement of micrometer-sized filler particles) can be significantly changed in external magnetic fields if the matrix is soft. This restructuring of the filler is noticeable on the free surface of an MAE sample and the corresponding changes of surface properties (e.g. wettability or adhesion) can be useful for a wide range of applications, e.g. liquid manipulation in microfluidic devices or magnetically controllable cell culture substrates etc.. The primary goal of this project is to investigate magnetic field induced surface changes (e.g. its topography) of MAE materials and establish the general relationships between physicochemical properties of constitutive components of a composite material (i.e. matrix and filler, including their interfaces) and the resulting modifications of surface properties (e.g. wettability or spread reflection) in magnetic fields. The apparent macroscopic surface characteristics are determined by the microscopic properties of constitutive components of a composite material near its surface to be systematically varied. By doing so, a predictive design of the magnetic field responsive MAE surface should be enabled. The main work load of the present project will be systematic and thorough characterization (various surface microscopy methods, optical profilometry, surface scattering techniques, etc.) of magnetic field induced surface changes of MAE and determination of the correlation between surface properties of the composite materials and bulk (magnetorheological and magnetic properties, composition of the filler etc.) properties of their constitutive components. The matrices will be polydimethylsiloxane-based. The filler composition will comprise micrometer-sized soft-magnetic (iron) and/or hard-magnetic (NdFeB) particles of variable size and morphology (spheres, flakes) enhanced by ultrafine (nano-) and fine magnetic particles (e.g. spinel ferrites). The surface properties of particles will be tuned, e.g. for increasing their hydrophobicity or functionalization. The experimental results will be compared with conclusions of recent mesoscopic theoretical approaches in order to verify their validity and identify their limits. To emphasize the structure-property-function relationships, the measurements will be performed in the context of three possible application areas of MAE materials with external magnetic field control: i) tunable surface wetting, ii) erasable and reconfigurable diffractive optical elements, and iii) tunable alignment layers for liquid crystals. The latter application will be used to detect the relaxation behavior of the microscopic filler in the layers adjacent to the surface after switching off the external field. Long-term observations of material performance will be made in order to make conclusions about the aging/degradation of functional surface properties and the underlying physicochemical mechanisms of it.