Liquid Crystal Phase Behaviors Of Nanoplatelets And Their Mixtures

Due to the development of the material synthesis process,the family of two-dimensional materials is becoming larger,including emerging graphene,MXene,MoS2,black phosphorus and so on.Self-assembling properties of the two-dimensional particles often be utilized when constructing functional materials or devices,so dicotic liquid crystals have become a hot research topic in the field of functional soft condensed matter.The self-assembly properties of discotic liquid crystal mixing system and the control of phase change process and phase structure are important pioneers in the application of two-dimensional materials,and this study will use zirconium phosphate(ZrHP)as a template particle of two-dimensional material to study the effects of ion concentration,rods and spherical particles on phase transition.In addition,magnetic field,as an important method of controlling particle’s orientation,is of great significance for the construction of functional materials and devices with two-dimensional nanomaterials as the unit.Therefore,we will induce ZrHP nanoplatelets to re-orientation with magnetic fields to obtain a single domain,and use ferromagnetic nano-discs to enhance the magnetic response of the chiral phase.Here’s what it’s all about:1 The effects of pH value changes caused by the introduction of TBAOH and TBAC1 on discotic liquid crystal’s stability and LC phase were studied,and the ion concentration of disc-shaped liquid crystals was regulated by TBAOH and TBAC1 mixtures,and the effects of different ion concentrations on discotic liquid crystal phase transition process and phase behavior were studied.The study found that when pH<6.02±0.31,ZrHP become instability,when pH>8.5±0.4,due to the solubility in alkaline conditions of ZrHP and particle size decreased,or even disappeared.This finding is of great guiding the using of ZrHP in research work or practical application.In addition,by the ion concentration--volume fraction phase diagram,the increase of ion concentration will increase the discotic liquid crystal I,as well as I-N1 phase transition interval,I-N1-N2 three-phase coexistence interval decreased.By introducing the effective volume of the particles,we find that the reason why the ion concentration causes the phase transition rate to decrease is to reduce the effective ratio of thickness to diameter of the particles.Therefore,in ion insensitive systems,the phase transition rate can be controlled by regulating ions,which is of great significance to the study of liquid crystal structural materials,such as graphene fibers,films,etc.2 The phase transition path of the three-phase coexistence zone of the discotic system is studied by using the free energy minimization and free energy landscape.Size ratio of these two particles used in the experiment was 0.2310,and the phase diagram of the spheres volume fraction-nanoplatelets volume fraction was drawn by observing and analyzing the phase transition process,which included three-phase coexistence and isotropic-isotropic(I-I)coexistence zone.Based on the semi-grand potential theory,the phase diagram is converted to the semi-grand system to remove the influence of spherical particles on the system,and the free energy landscape is successfully drawn,which establishes the connection between free energy and phase transition process.In the three-phase coexistence area,three different phase change paths are found,combined with the analysis of free energy landscape,to achieve the unity of theory and experiment.staged phase transition process of the three-phase coexistence zone is found.The uniform phase will first form the metastable phase and then continue to separate to achieve phase equilibrium.This study proves that the free energy landscape method of the sphere-polymer system can be extend to discotic system and is of great significance to the theoretical study of the discotic liquid crystal mixing system.3 Introducing the chiral CNC as depletant into the ZrHP discotic liquid crystal,the phase behavior of the rod-nanoplate mixing system is studied and the phase diagram is obtained As can be known from the phase diagram of the discotic mixing system,the introduction of CNC makes I-N coexistence region wider.Because shape anisotropic of CNC enable it to form a liquid crystal phase,it prefers to form N-N coexistence.In addition,a spontaneous core-shell structure with a CNC shell and ZrHP core is observed.The schematic structure of CNC-ZrHP core-shell structure is figure out by the application of wave plate and the information of simulation of ZrHP droplet structure.According to the free energy landscape,the CNC appears as a protective phase to achieve three-phase coexistence because nanoplatelets-rich N+and I phase cannot coexist.4 The self-assembly of the discotic liquid crystal is controlled by the the magnetic field and gravity.With the interaction of uniform magnetic field,the monodomain of ZrHP colloid reorient to single-domain structure,which proves the anisotropic of magnetic susceptibility of ZrHP single-layer nanoplates is positive.By extending the gravity length of the nanoplatelets to change the density,an interesting pattern with an interference color band is achieved under the interaction of a magnetic field.Based on this color band,the density profile of nanoplatelets in N is obtained by combining experiment and calculation.Interference color band as a promising optical phenomenon can be used as a simple method of experimental measure state equations.By comparison,the osmotic pressure function of nanoplatelets volume fraction has a high degree of matching with the theoretical prediction state equation of hard disk model.At higher volume fraction,the experimental value is positively deviated from the theoretical value,possibly due to the quasi-equilibrium state,the polydispersity and surface charge of particles This research lays an important foundation for the basic understanding of extra filed control 2D colloids(graphene,graphene oxide,MXene etc.)and provides new opportunities for the application of soft matter optics and the development of intelligent advanced functional materials.5 In this study,we used 2D ferromagnetic nanoplatelets to enhance manipuility of CNC in magnetic fields,successfully obtained chiral monodomain with a perfect alignment in a weak magnetic field(0.1-0.5T).In the mixture with CNC and BF,when there is a gradient magnetic field,the direction of motion of the tactoid depends on the competition between gravity and the magnetic field acceleration,i.e.the direction of the ∑grav-∑mag.By adjusting the magnetic field strength and the concentration of magnetic particles,the direction and position of the tactoid can be regulated,and the rate of separation can be controlled.The discovery provides a new way to control particle self-assembly and liquid crystal phase transition processes to build new devices and materials.In addition,with the interaction of magnetic field,hydrogels with paranematic structures are successfully prepared by photo-curing.It is found that the hydrogel has stress-color response.With the change of stress,its birefringence color changes due to the change of the orientation and density of the internal nanoparticles.Different from the nematic phase hydrogel,the para-nematic phase hydrogel in the relaxed state without birefringence phenomenon and presents the dark color(no polarization light through).When the stress act on the paranematic hydrogel,the nanoplatelets reorient and order parameter increase,birefringence color appears.Due to the change of material morphology,the structural parameters increase higher than the nematic phase,so its color change range is wider.This unique optical property has significant application potential in sensors and color-changing materials.