Woods Mackenzie B, Beidaghi Majid, Davis Virginia A
Department of Chemical Engineering, Auburn University, Auburn, Alabama 36849, United States.
Department of Mechanical and Materials Engineering, Auburn University, Auburn, Alabama 36849, United States.
Langmuir. 2024 Feb 13;40(6):2907-2917. doi: 10.1021/acs.langmuir.3c02851. Epub 2024 Jan 29.
Understanding the dispersion behavior of MXenes is interesting from a fundamental colloid science perspective and critical to enabling the fluid-phase manufacturing of MXene devices with controlled microstructures and properties. However, the polydispersity, irregular shape, and charged surfaces of MXenes result in a complex phase behavior that is difficult to predict through theoretical calculations. As two-dimensional (2D) nanomaterials, MXenes can form lyotropic liquid crystal phases, gels, and aggregates. This work aims to elucidate the effects of MXene (TiCT) sheet size on their phase behavior and associated rheological properties. Aqueous dispersions of large sheets with an average lateral dimension of 3.0 μm, small sheets with an average lateral dimension of 0.3 μm, and a bimodal mixture of the two sizes were investigated by using cross-polarized optical microscopy and rheology. At low concentrations, the large MXene dispersions exhibited lyotropic liquid crystal behavior and extended aligned textures, but increasing concentration resulted in the formation of dense flocs. Dispersions of small sheets formed small birefringent domains with increasing concentration but lacked long-range ordering. A bimodal mixture of these sizes enabled the formation of liquid crystalline phases with extended aligned textures with less floc formation. These results provide insights into using polydispersity to tune dispersion microstructure and rheological properties that can be applied to designing dispersions for fluid-phase manufacturing methods, such as direct ink writing.
从基础胶体科学的角度来看，了解MXenes的分散行为很有趣，而且对于实现具有可控微观结构和性能的MXene器件的液相制造至关重要。然而，MXenes的多分散性、不规则形状和带电表面导致了复杂的相行为，难以通过理论计算进行预测。作为二维（2D）纳米材料，MXenes可以形成溶致液晶相、凝胶和聚集体。这项工作旨在阐明MXene（TiCT）片层尺寸对其相行为和相关流变性能的影响。通过使用交叉偏振光学显微镜和流变学研究了平均横向尺寸为3.0μm的大片、平均横向尺寸为0.3μm的小片以及这两种尺寸的双峰混合物的水分散体。在低浓度下，大尺寸MXene分散体表现出溶致液晶行为和扩展的取向织构，但浓度增加会导致形成致密的絮凝物。小片的分散体随着浓度增加形成小的双折射域，但缺乏长程有序。这些尺寸的双峰混合物能够形成具有扩展取向织构且絮凝物形成较少较少的液晶相。这些结果为利用多分散性来调节分散体的微观结构和流变性能提供了见解，可应用于设计用于液相制造方法（如直接墨水书写）的分散体。
