Counterion-regulated Lyotropic Liquid Crystal Structures Of Polymerizable Ionic Gemini Amphiphilic Molecules

Gemini amphiphiles are a special class of molecules that consist of two covalently linked ingle-chain amphiphiles.When used as surfactants,they display superior properties over their traditional single-chain counterparts,such as ultralow surface tension and critical micelle concentration,and relatively high foaming and emulsifying capabilities.Due to their unique structures,Gemini amphiphiles can self-assemble in water solutions into a rich variety of aggregate morphologies.There is a great opportunity to vary the self-assembled structures by suitable molecular engineering in the Gemini amphiphiles,which may find specific applications.Lyotropic liquid crystals derived from the mixing of Gemini amphiphiles and water have attracted intensive interest in the research field of self-assembly.It has been found that they show a high tendency to form unconventional liquid crystal phases,for instance,those with non-uniform interfacial curvature.In addition,since Gemini molecules contain two hydrophobic chains,self-cross-linkable abilities can be realized by chemically attaching polymerizable groups to the hydrophobic chains.Therefore,liquid crystals formed by polymerizable Gemini amphiphiles can be photocured with high-fidelity structural retention by free-radical polymerization,thereby providing a feasible approach to the preparation of ordered nanostructured polymers.For ionic Gemini amphiphiles,the controllable factors in the molecular structures include ydrophilic head groups,alkyl chains,linking groups,and counterions.Among them,through simple and efficient ion exchange,the interactions between counterions and hydrophilic head groups can be finely tuned,and the self-assembled aggregates of Gemini amphiphiles can be tailored.The aim of this thesis is to rigorously understand the influence of counterions in Gemini mphiphiles on their self-assembled structures.Our experimental results demonstrate that for both polymerizable and non-polymerizable amphiphiles,the corresponding aqueous lyotropic liquid crystals can be indeed effectively regulated by changing the counterions.For example,the phase windows of the lyotropic liquid crystal can be widened using certain counter ions.In particular,bicontinuous cubic gyroid phases,which are considered difficult to obtain,can be also generated.Furthermore,the use of polymerizable Gemini amphiphiles can enable the structural retention of the ordered liquid crystals by photocuring.The research contents are as follows:First,non-polymerizable quaternary ammonium Gemini amphiphiles with different ounterions were designed and synthesized.Using small-angle X-ray scattering,we investigate the self-assembled lyotropic liquid crystals formed by their water solutions.Counterions under investigation include bromide ions and the tartrate derivatives.The variation of the counterions enriches the lyotropic mesomorphism of the amphiphilic molecule.In addition to the hexagonal columnar(H₁)phase,two cubic mesophases,i.e.,the HCP and A15 phase are obtained.Secondly,polymerizable quaternary ammonium Gemini amphiphiles with different ounterions were designed and synthesized.We systematically studied the self-assembled behavior of lyotropic liquid crystals.Methacrylate was attached at the tip of the hydrophobic tail as the polymerizable group to afford the polymerization of the formed liquid crystals.We categorize the counterions by the valence state for our studies.The monovalent counterions include bromide,dihydrogen phosphate,acetate,methanesulfonate,trifluoromethane acetate,and trifluoromethanesulfonate.We have found lamellar(L_?)and H₁ phases in this category of Gemini amphiphiles.The divalent counterions under investigation are rod-shaped,acid radical,rigid,and chiral.We realize the formation of bicontinuous cubic gyroid structures with a concentration window of about 5%,which is practically broad.We systematically study by SAXS the mesophase phase structures,such as the counterion-dependent lattice constants of specific mesophases at the same concentration.Finally,the bicontinuous cubic phases formed by G6-Y were fixed by UV-induced olymerization,leading to the generation of polymeric materials with 3-D interconnected nanochannels.As confirmed by SAXS characterization,high-fidelity structural lock-in has been achieved after polymerization.The resultant polymers may find potential applications in membrane filtration.