• Yizhen Shao

Student thesis: Phd


This thesis presents the research of graphene oxide (GO) and cetrimonium bromide (CTAB) hybrid systems from the initial impact of the two materials in liquid phase, to the formation of colloidal systems of liquid crystals. The aim is to study the interactions between GO and CTAB and their fundamental physiochemical properties, and to create ordered colloidal assemblies with novel structures and functionality. It is found that the initial impact of GO with CTAB in aqueous phase yields vortex ring (VR) effect, leading to the formation of GO-VR microparticles with complex axially symmetric shapes such as spheres, donuts and jellyfish, and their optimum conditions can be obtained by varying the preparing conditions such as the flake size of GO sheets and concentrations of GO and CTAB. The overall shape of the GO-VR microparticles is determined early on under the influence of the impact and viscous friction forces. It is demonstrated that the surface charge on GO sheets interacting with CTAB molecules generates an electrohydrodynamic VR effect, driving the formation of a core-shell structure in GO-VR microparticles. The shell is comprised of densely packed and aligned GO flakes and the core is comprised of a low-density arrangement of randomly oriented GO flakes. Both the thickness of the shell and the density of flakes in the core (including a hollow core) can be controlled by varying preparing parameters such as the settling time and GO concentration. A similar cationic surfactant DODAB, anionic surfactant SDS and plan water do not result in stable and structured GO-VRs. The CTAB-decorated GO-VR aerogels are found to be efficient for the adsorptive elimination of anionic contaminants from water. Further into the colloidal systems of GO and CTAB, the formation of lyotropic liquid crystals (LLCs) of both GO and CTAB are demonstrated and characterized at varied concentrations, temperatures or confinement conditions, and a series of LLC phase diagrams are established for a CTAB/GO/water ternary system covering various LLC phase transitions from isotropic to different lyotropic phases. It is corroborated that an LLC structural transition from GO-doped CTAB LLCs to an interpenetrating hybrid CTAB/GO LLCs takes place when a critical concentration of GO at 0.75 wt.% is reached, forming a nematic phase of GO. The LLC hexagonal and cubic phases of CTAB are stabilized by the interpenetrating hybrid structure as GO sheets are aligned orderly, while a stabilization of CTAB lamellar phase occurs from doping even for a comparatively low GO loading of 0.083 wt.%. The alignment of CTAB/GO LLCs can be regulated through the orientation of GO sheets in the system. Oscillatory rheology measurements reveal that the elastic properties of CTAB/GO/water mixtures are significantly enhanced by increasing GO loading, as the GO sheets strongly increase the interactions within the LLC microstructure.
Date of Award1 Aug 2022
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorIngo Dierking (Supervisor) & Aravind Vijayaraghavan (Supervisor)

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