Zhejiang University's advanced team has made new progress in the non spherical assembly of graphene oxide liquid crystals

Liquid crystal material is a kind of material widely existing in nature and man-made materials It has a wide range of applications in display screen, sensor, intelligent elastic material and other fields For liquid crystal materials, the key to study the theory of liquid crystal and to control the properties of liquid crystal materials is to adjust the internal orientation structure and topological conformation The existing research methods are generally to limit the liquid crystal in a highly symmetrical space, such as spherical, ellipsoid, cylindrical, to explore its three-dimensional topology Liquid crystal materials have the properties similar to elastomers If we want to confine the liquid crystal in the complex non spherical three-dimensional space, it will cause great elastic distortion Therefore, it is difficult for the complex non spherical liquid crystal assembly to exist stably So far, it is still a great challenge to prepare liquid crystal assembly with complex geometry and explore its internal topological conformation Recently, Zhejiang University Gao Chao, Xu Zhen team and other collaborators (Professor Zheng Qiang and Professor Song Yihu of Zhejiang University) worked together to prepare a variety of non spherical liquid crystal assemblies with complex geometry by drop impact assembly (DIA) on the basis of previous work, and studied their internal topological structure and forming mechanism Fig 1 (a) schematic diagram of dia process and (B, c) uniform and stable jellyfish like and hazelnut like liquid crystal assemblies prepared on a large scale (source: ACS Nano) through the method of DIA, the graphene oxide liquid crystal was dropped into the solidification bath containing calcium chloride, and the graphene oxide liquid crystal assembly with different shapes was prepared Dia process is widely used in the field of liquid assembly By adjusting the drop height and liquid surface tension, various transient structures with different shapes can be obtained The unique shear thinning behavior of the graphene oxide liquid crystal makes the sheet in the graphene oxide droplet orientation effectively under the impact At the same time, the rich oxygen functional groups on graphene oxide also help the droplets rapidly form gelatin under the action of cations, thus maintaining the rich shape and structure formed during impact Fig 2 (a) morphology of liquid crystal assembly obtained under different dropping height and concentration conditions; and (b) phase diagram of preparation of non spherical liquid crystal assembly (source: ACS Nano) Fig 3 geometric morphology and topological conformation of different shapes of assembly: (a) tear shape, (b) hazelnut shape, (c) bowl shape, (D, f) jellyfish shape, (E) flower shape (source: ACS Nano) thanks to the unique birefringence phenomenon of liquid crystal, the team conducted real-time observation on the dia process through polarized high-speed imaging technology, and further explored the forming mechanism of different shape assemblies The researchers studied the effect of drop height and graphene oxide solution concentration on the drop shape Through the summary of a large number of experimental data, the corresponding phase diagram was obtained, which provided a guiding idea for the preparation of complex shape liquid crystal assembly by dia method In addition, the preparation method is extended to graphene oxide / sodium alginate, graphene oxide / ferric oxide and other composite systems, further expanding the application scope and functionality of this method Fig 4 heteromorphic composite liquid crystal assembly (A-C) different arrangements of graphene oxide / sodium alginate composite assembly; (d) magnetic heteromorphic composite assembly prepared by graphene oxide / ferric oxide (source: ACS Nano) the achievement of this achievement also benefits from the accumulation of excellent team and learning from previous work As early as 2011, the research team discovered the liquid crystalline nature of graphene oxide and used it to spin, thus opening up the research field of graphene oxide liquid crystal and its macro assembly Related work includes (ACS Nano 2011, 5, 2908; NAT Commun., 2011, 2, 571; acc chem Res., 2014, 47, 1267-1276; chem Rev., 2015, 115, 7046 − 7117; adv mater., 2016, 28, 7941) The related achievements were published on ACS Nano under the title of "nonsphere drop impact assembly of graphene oxide liquid crystals" The first author of the paper is Yang Qiuyan, a postdoctoral fellow of the superb team At present, he works in West Lake University, and the co first author is Jiang Yanqiu, Ph.D of the superb team Professor Zheng Qiang and Professor Song Yihu from the Department of polymer science and engineering of Zhejiang University provided strong support and cooperative guidance for the completion of this work The thesis is supported by the national key R & D plan and NSFC.