Construction And Applications Of Functional Surfactant Ionic Liquid Crystals

Ionic liquid crystals(ILCs)are ionic compounds with thermotropic liquid crystal(LC)properties,showing the tendency to self-assemble to form ordered structures in a certain range of temperature.Compared with traditional thermotropic LCs formed by covalent compounds,ILCs exhibited the advantages of simple synthesis,flexible components and adjustable properties and received extensive attentions in recent years.Surfactant molecules with long alkyl chains usually have excellent self-assembly behaviors,and can be used as the flexible part of ILCs to combine with different rigid groups,resulting in ILC materials with fascinating functions.ILCs integrate the properties of the components and their highly ordered assembly structures,being conducive to optimizing the overall performance of materials.However,at present,surfactant-based ILCs are limited in types and the unicity in functions,and therefore it is necessary to explore more functional groups and surfactants to construct ILCs.In this thesis,we chose surfactants as one of the basic building blocks to interact with different rigid functional groups,preparing a series of novel ILCs and investigating their formation conditions,self-assembly mechanisms and potential applications in detail.The contents of this dissertation are as follows:Chapter I is a comprehensive introduction of the research background.Based on the conception of self-assembly,we described the characteristics and importance of self-assembly.The concepts,types and self-assembly behaviors of surfactants were systematically introduced.We summarized the conception,classification,properties and characterization method of LCs,especially thermotropic LCs and ILCs.The building blocks,basic properties and functional applications of surfactant-based ILCs were reviewed in detail.Finally,we pointed out the research purpose,contents and scientific significance of the dissertation.In chapter ?,we chose cationic surfactant(C7H15)4N+Br-to interact with K7PW11O39,preparing a cubic ILC[(C7H15)4N]7PW11O39,which exhibited good thermostability,excellent mechanical strength and high viscosity.The ILC could adhere to a variety of metal surfaces,such as Cu and Fe,and thus could be used as an anti-corrosion coating for metal protection.For the ILC-coated metals,polarization curve tests showed that the corrosion voltage increased and the corrosion current decreased,indicating the corrosion resistance of metals was enhanced.Electrochemical impedance results showed that the resistance increased and the capacitance decreased when metals were coated with the ILC,proving that the ILC coating inhibited the corrosion of metals.The ILC constructed in this work was environmentally friendly and could be reused,providing potential applications in the protection of metal materials such as buildings and cultural relics.In chapter III,we used cationic surfactants with different alkyl chain length to combine with guanosine 5'-monophosphate disodium(GMP),resulting in four GMP-surfactant ionic compounds.All the ionic compounds exhibited thermotropic LC properties and the length of surfactant alkyl chains was found to be of great importance in modulating LC phases.Smectic A(SmA)and columnar rectangular(Colr)phases were formed upon increasing the length of the aliphatic chains due to the enlargement of the steric hindrance.In addition,the introduction of K+ ions could induce the phase transition of LCs from the SmA or Colr mesophase to a columnar hexagonal(Colh)mesophase,which was attributed to the formation of G-quadruplexes in GMP-surfactant-K+ complexes.Accordingly,the chirality and fluorescence properties of the complexes also exhibited K+-responsive characters as the phase transition of the LCs emerged.The ILCs containing biomolecules constructed in this system were hopeful to fabricate smart luminescent materials and biosensors.In chapter ?,two polymerizable surfactants with different number of double bonds,3-undecylene-1-vinylimidazolium bromide(C11VIMBr)and 3-dodecyl-1-vinylimidazolium bromide(C12VIMBr),were chosen to prepare magnetic surfmers by introducing MnCl2,GdCl3 and HoCl3.The magnetism of the surfmers changed with the types of metal ions.All the magnetic surfmers showed thermotropic LC behaviors within a certain range of temperature.The microstructures of the ILs depended on the types of magnetic counterions and organic cations.The magnetic LC films with ordered nanostructures were directly obtained by in situ polymerization of the magnetic surfmers without significant change of magnetic strength.The magnetic LC films obtained could be attracted and removed by external magnet,providing a possibility for the development of magnetically responsive solid electrolytes and efficient adsorbents.In chapter V,we prepared three kinds of fluorescent magnetic ILCs with manganese(?)halide complex anions as luminescence centers and cationic surfactants with different alkyl chain length as cations.The three ILCs showed green,red and yellow emission,respectively,with the increasing alkyl chain length at room temperature.All the ILCs experienced a phase transition from crystal to LC phase during heating process,accompanied with the emission color changed from green or yellow to red,which was ascribed to the structural transition of the complex anions.Such thermochromic response was fast,reversible and stable,and more importantly,rarely reported for Mn-based luminescent substances.Furthermore,the emission intensity of the ILCs was sensitive to water and some organic vapors.Fluorescent papers loaded with these ILCs were prepared in a facile way,which could perfectly retained the fluorescent properties of the ILCs,and thus could be used as temperature indicators,humidity or organic vapor sensors.