One-step formation of three-dimensional interconnected T-shaped microstructures inside composites by orthogonal bidirectional self-assembly method

The fillers inside a polymer matrix should typically be self-assembled in both the horizontal and vertical directions to obtain 3-dimentional (3D) percolation pathways, whereby the fields of application can be expanded and the properties of organic-inorganic composite films improved. Conventional dielectrophoresis techniques can typically only drive fillers to self-assemble in only one direction. We have devised a one-step dielectrophoresis-driven approach that effectively induces fillers self-assembly along two orthogonal axes, which results in the formation of 3D interconnected T-shaped iron microstructures (3D-T CIP) inside a polymer matrix. This approach to carbonyl iron powder (CIP) embedded in a polymer matrix results in a linear structure along the thickness direction and a network structure on the top surface of the film. The fillers in the polymer were controlled to achieve orthogonal bidirectional self-assembly using an external alternating current (AC) electric field and a non-contact technique that did not lead to electrical breakdown. The process of 3D-T CIP formation was observed in real time using in situ observation methods with optical microscopy, and the quantity and quality of self-assembly were characterized using statistical and fractal analysis. The process of fillers self-assembly along the direction perpendicular to the electric field was explained by finite element analogue simulations, and the results indicated that the insulating polyethylene terephthalate (PET) film between the electrode and the CIP/prepolymer suspension was the key to the formation of the 3D-T CIP. In contrast to the traditional two-step method of fabricating sandwich-structured film, the fabricated 3D-T CIP film with 3D electrically conductive pathways can be applied as magnetic field sensor. A one-step electric field-induced self-assembly method was developed to efficiently control the self-assembly of fillers along two orthogonal axes to form three-dimensional interconnected T-shaped microstructure assembles of carbonyl iron powder inside a polymer matrix.聚合物基体（polymer matrix）内的填充剂通常需沿水平与垂直方向自组装，以构建三维（3D）渗流通路，进而拓展应用场景并优化有机-无机复合薄膜的综合性能。传统介电泳（dielectrophoresis）技术通常仅能驱动填充剂沿单一方向实现自组装。本研究开发了一种一步法介电泳驱动策略，可有效诱导填充剂沿两个正交轴方向自组装，最终在聚合物基体内形成三维互连T形铁微结构（3D-T CIP）。针对嵌入聚合物基体的羰基铁粉（carbonyl iron powder, CIP），该策略可使填充剂沿薄膜厚度方向形成线性结构，并在薄膜表面构建网络结构。研究通过外加交变电流（alternating current, AC）电场与无接触式工艺实现了对聚合物内填充剂的调控，使其实现正交双向自组装，且该过程不会引发电击穿。本研究借助光学显微镜原位观测手段，实时追踪了3D-T CIP的形成过程，并通过统计分析与分形分析表征了自组装的数量与质量。通过有限元模拟分析，阐释了填充剂沿垂直于电场方向自组装的机制；结果表明，电极与CIP/预聚物悬浮液之间的绝缘聚对苯二甲酸乙二酯（polyethylene terephthalate, PET）薄膜是3D-T CIP形成的关键因素。与传统制备三明治结构薄膜的两步法相比，所制备的具备三维导电通路的3D-T CIP薄膜可作为磁场传感器使用。本研究开发了一种一步法电场诱导自组装策略，可高效调控填充剂沿两个正交轴方向自组装，最终在聚合物基体内形成羰基铁粉的三维互连T形微结构组装体。