Lattice Self-assembly Systems Based On Zwitterionic Amphiphiles And Polyoxometalates

The regulation of noncovalent interactions is an important basis for the realization of controllable self-assembly and the construction of functional materials through self-assembly.The inorganic-organic co-assembly system combines the diversity of functional groups of organic assembly units and functional diversity of inorganic assembly units,so the selection of suitable organic-inorganic building blocks and the regulation of noncovalent interactions between different components to obtain organic-inorganic co-assembled materials is of great significance for the development of new supramolecular materials.In recent years,the application of lattice self-assembly systems based on organic-inorganic building blocks in the fields of chiral light-emitting materials and new protein-mimicking materials has attracted extensive attention of researchers.Based on the previous work of our group,this paper focuses on the regulation of lattice self-assembly of imidazole-type zwitterionic amphiphiles and polyoxometalates.Zwitterionic amphiphiles have high polarity and strong hydration ability,and as building blocks for self-assembly can endow hydrogels with unique functions.Polyoxometalates are nano-sized clusters of inorganic transition metal oxides with diverse compositions,structures,and functions.By tracking the lattice self-assembly process,regulating the structure of zwitterionic amphiphiles and introducing host-guest interaction,the interactions between assembly elements was adjusted to further clarify the influence of the strength and direction of noncovalent interactions on the lattice self-assembly system.This thesis consists of three parts:Part 1:The research status of self-assembly systems regulated by various noncovalent interactions and organic-inorganic co-assembly systems involving polyoxometalates are introduced.The research and application of lattice self-assembly systems are emphasized.Part 2:It was found that when the imidazole-type zwitterionic amphiphilic molecule C16IPS and polyoxometalate(phosphotungstic acid,HPW)were co-assembled in aqueous solution,the structure of the assembly was transformed from a crystalline fiber to an amorphous micellar network.This work explores intermediate transition states.It was found that when the molar ratio of C16IPS to HPW was 3:1,the morphology of the aggregates changed from disordered to ordered cross-woven structure as the concentration of C16IPS increased.When the molar ratio was increased to 4:1,the aggregates became more compact with the increase of C16IPS concentration,and a highly parallel structure was obtained.The interaction in the assembled system under these two molar ratios was further enhanced and directional,and obvious lattice self-assembly occurred.The SAXS spectra was also in good agreement with the observed morphology of the aggregates.The results of the surface tension test showed that in the transition state,with the increase of C16IPS concentration,the surface tension value first decreased and then increased.In the rising stage,there is a strong hydrogen bond between the HPW molecules on the surface of the aggregate,which reduces the number of free C16IPS molecules in aqueous solution,and the molecules in the gas-liquid adsorption layer continue to enter the aqueous solution,and the surface tension value increases.Part 3:Four type of zwitterionic amphiphiles with different head groups and alkyl chain lengths were assembled with phosphotungstic acid and cyclodextrin in aqueous solution,respectively.The molar ratio of zwitterionic amphiphiles and cyclodextrin was fixed as 1:1 according to the results of isothermal titration calorimetry(ITC).The assembly of hollow tubes and fiber networks were obtained by changing the molar ratio of the added phosphotungstic acid.The differences in the crystal structures of different assemblies were compared by X-ray diffraction(XRD)and the changes in the cyclodextrin stacking patterns were found during the assembly process.FTIR and 1H NMR spectra show that hydrogen bonding,electrostatic interaction and host-guest interaction exist simultaneously in the assembled system.Finally,the effects of amphiphilic head group structure and carbon chain length on the mechanical properties and stability of the gel were proven by rheology and differential scanning calorimetry(DSC).