Intelligent colloidal superliquid crystal by liquid shearing micro printing

Background as a common liquid, water molecules are in rapid motion The ancient sayings such as "cut off the water and make it flow", "time flies like this, day and night", "people can't step into the same river twice" vividly describe the fluidity of liquid Due to the fast free movement and short relaxation time of the molecules in the liquid, it is very difficult to achieve free printing or engraving in the liquid without external field stability, and to build a certain pattern Recently, the team of Professor Gao Chao and researcher Xu Zhen from polymer Department of Zhejiang University realized precision printing in graphene oxide aqueous liquid crystal to prepare stable three-dimensional pattern Although the water content of the solution is more than 99.5%, the pattern can have stable long-period order like solid crystal and super material The author defines it as super liquid crystal or liquid crystal Liquid crystal is a kind of intermediate phase between solid and liquid, which has the fluidity of liquid and the partial order of solid Liquid crystal materials are widely used in various natural and artificial materials, such as display screen, sensor, intelligent elastic material and so on For liquid crystal materials, the key to study the theory of liquid crystal and adjust the properties of liquid crystal materials is to adjust the internal orientation order structure However, the introduction of oriented ordered structure will cause large elastic distortion in the liquid crystal, so that these structures are very unstable in energy, which must be maintained by external stimulation, such as electric field, magnetic field, surface anchoring effect of the substrate, etc there is no effective way to get the stable oriented ordered structure in the free state As a typical two-dimensional material, graphene oxide will spontaneously form nematic liquid crystals when it reaches a certain concentration in a good solvent The existence of liquid crystal phase brings great convenience to the assembly of graphene oxide into macro materials, and the adjustment of the orientation of graphene sheets in the liquid crystal of graphene oxide has a great influence on the properties of graphene assembly The existing control methods are generally realized by using high-intensity electric field, magnetic field or laser, but these methods have high energy consumption, poor accuracy and low efficiency, and the stability of these orientation structures also depends on the external field to maintain, which greatly limits the application of graphene liquid crystal materials Research highlights: 1) stable direct writing printing was realized in low viscosity liquid for the first time, and it was found that the relaxation time of liquid crystal was directly related to the phase transition behavior, which opened a new idea of direct printing pattern of liquid crystal; 2) liquid shearing micro printing was invented, which was combined with 3D printing programming and manufacturing to realize the three-dimensional free control of liquid crystal orientation structure; 3) The concept of liquid super material and super liquid crystal is put forward The colloidal liquid crystal, super material and quasicrystal are combined to create the super liquid crystal material with various symmetrical structures Recently, on the basis of previous work, the team of Zhejiang University Gaoshi (Joint Communication) and Xu Zhen (Joint Communication) adopted a new shearing microlithography (SML) to realize the efficient and high-precision control of the internal orientation structure of graphene oxide liquid crystal At the same time, the researchers have further extended this method to a variety of colloidal liquid crystal systems, which makes SML have the potential to become a universal new technology for controlling the orientation of liquid crystal Figure 1: (a) schematic diagram of SML process (b) Schematic diagram of orientation structure obtained by SML (source: Nat Commun.) as an anisotropic material, liquid crystal has various anisotropic responses to various external stimuli such as electric field, magnetic field, laser, shear force, etc Based on this characteristic of liquid crystal materials, the researchers proposed a SML method: using a mechanical arm to control the micrometre probe to move in the liquid crystal to generate a shear field, and then using the anisotropic response of liquid crystal materials to the shear field to achieve the orientation regulation of liquid crystal elements (Figure 1) Compared with other existing technologies (such as electromagnetic field, laser, substrate surface patterning, etc.), SML realizes the orientation of liquid crystal elements through shear force, does not need the assistance of electromagnetic field with great energy consumption, and the production cost is low At the same time, SML technology process is simple, fast and easy to operate It has high precision of orientation structure regulation, wide application system and good application prospect Fig 2: (a, b) graphene oxide superlattice with typical Bravais lattice (c) Schematic diagram of super liquid crystal elements (D-G) graphene oxide superlattice with quasicrystal lattice (source: Nat Commun.) further study found that: in the graphene oxide liquid crystal system, by selecting the appropriate concentration range, the controllable orientation structure obtained by SML can be independent of the external field, and can exist independently and stably Graphene oxide superliques with both orientation ordering and certain position ordering are obtained (Fig 2) This discovery breaks the understanding that the traditional liquid crystal materials only have orientation order but no position order, and brings new ideas for further study of liquid crystal physics and the application of liquid crystal materials The researchers pointed out that graphene oxide superlattice is a typical dynamic stability structure, which is mainly realized by the huge molecular motion energy barrier caused by the large repulsion volume of graphene sheet, which is essentially different from most of the existing thermodynamically stable liquid crystal orientation structures (Figure 3) Fig 3: (a, c) liquid crystal phase transition of graphene oxide Relaxation behavior of (B, D, e) graphene oxide liquid crystals with different concentrations (source: Nat Commun.) thanks to the free programming feature of 3D printing technology, researchers have also prepared graphene oxide super liquid crystal with stable micron level pattern by using SML technology The graphene oxide superliquid with multilayer structure and three-dimensional structure is realized by means of layered assembly and changing the probe angle, which further expands the application scope of SML Technology (Figure 4) Fig 4: (a, b) graphene oxide super liquid crystal with complex patterns and characters (c) Graphene oxide superliques with Moire fringes were prepared by layered assembly (d) Graphene oxide superlattice with three-dimensional structure (source: Nat Commun.) in addition, the researchers have further explored the subsequent structural evolution and application of this superliquid It is found that the orientation structure in the superliquid will undergo a rearrangement folding process during the drying process, and finally form a fold structure similar to the ridge shape Based on this discovery, graphene oxide film with patterned fold structure was prepared by using graphene oxide superliquid crystal, and the effective control of mechanical and electrical properties of graphene oxide film was realized (Figure 5) Fig 5: (a) changes in the drying process of the structural units of the super liquid crystal (B-D) the structure of the structure unit after drying The effect of (e-k) superliquid structure on the mechanical properties of graphene oxide films (source: Nat Commun.) 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; chem Rev., 2015, 115, 7046; adv mater., 2016, 28, 7941; ACS Nano, 2019, 13, 8382; adv mater., 2019, 1902664 This achievement was published on nature communications (NAT Commun 2019, 10, 4111) under the title of "artistic colonial liquid metals by shelving microscopy" The first co authors of this paper are Jiang Yanqiu and Guo fan, Ph.D of the excellent team The thesis is supported by the national key R & D plan and NSFC.