Proton Conducting Materials Based On Normal-Type Self-assembled Amphiphilic Micelles

Proton conduction is critically important in many areas such as new energy technologies and bioinformatics.For instance,the proton conductivity exhibited by proton exchange membranes largely determines the performance of fuel cells.In these membranes,the presence of continuous nano-scale channels is essential for the efficient transport of protons.The proton transport channels in traditional proton exchange membranes are formed by segregation of ionic moieties and hydrophobic chains of the ionized polymers that results in the generation of reverse micellar nanostructures.Therefore,the proton conductivity strongly depends on high humidity,under which the reverse micellar nanostructures can be connected to form continuous ionic channels.Obviously,traditional proton exchange membranes suffer from the irregularly nanostructured ionic channels and the strong dependence on humidity.Materials derived from self-assembly of amphiphilic molecules,such as lyotropic liquid crystals(LLCs),can offer precisely controlled nanostructures and chemical environments for ionic transportation.LLCs with cylindrical,lamellar,and bicontinuous nanostructures have been utilized for ionic transportation.Whereas cylindrical and lamellar LLCs need to be macroscopically aligned for enhanced ionic conduction,access to the bicontinuous counterparts has been challenging.In view of the abovementioned challenges,this thesis focuses on the studies of the proton transportation behavior of LLCs and polymers derived from easily accessible self-assembled normal spherical micelles.The thesis is organized as follows:1.Multi-headed amphiphilic molecules BTSA-12 and BTSA-16 possessing three sulfonic acid groups and one hydrocarbon tail were designed and synthesis.The difference between these BTSA-12 and BTSA-16 was the chain length of the hydrocarbon tail.Self-assembled LLCs formed by hydration of amphiphilic molecules BTSA-12 and BTSA-16 were investigated using polarized light microscope(POM)and small-angle X-ray scattering(SAXS).In the LLCs formed by the self-assembly of BTSA-12 hexagonal cylindrical(H_I),Frank-Kasper A15 and a body-centered cubic(BCC)phases were found.Increasing the chain length of the hydrophobic tail from 12 to 16 carbons significantly changed the LLC behavior,as evidenced by the LLCs from BTSA-16 showing no ordered spherical micellar phases but possessing only hexagonal H_I phases.Electrochemical impedance spectroscopy was employed to measure the proton conductivities of the LLCs formed by BTSA-12 and BTSA-16.It was found that a BCC LLC by BTSA-12 possessed the highest conductivity of 1.8×10^-2 S/cm.2.Polymeric membranes with normal-type spherical micelles were prepared for proton transportation.Phytic acid(IP6),a six-fold dihydrogenphosphate ester,were utilized to construct polymerizable amphiphilic molecules(MAC2-IP6 and MAC11-IP6)by neutralization with alkyl tertiary amines.In these molecules,ionized amine and IP6 serve as the hydrophilic head.The carbon chain length of MAC2-IP16 and MAC11-IP6 were 2 and 11,respectively.The polymeric samples(PMAC2-IP6 and PMAC11-IP6)were obtained by mixing 85 wt.%amine salts,5 wt.%H₂O and10 wt.%PEG-DMA(crosslinker),followed by UV-induced radical polymerization.It was found through SAXS that the PMAC11-IP6 film has normal-type spherical micelles.The proton conductivities of the two membranes were measured at a fixed temperature of 60?under varied humidities.PMAC11-IP6 membrane exhibited higher proton conductivities than the PMAC2-IP6ones under the same humidity.The value reached 2.38×10^-1 S/cm under a 90%RH environment,being 2.1 times that of the commercial Nafion 117 membrane.3.In order to further stabilize the polymers for high-temperature(e.g.,above 100?)proton conduction,composite membranes were prepared by infiltration of commercial microporous polypropylene(PP)membranes(pore size of 20?m)with the gels consisting of MAC11-IP6(or MAC2-IP6),water,and PEG-DMA(crosslinker).Radical polymerization induced by UV was utilized to fix the micellar nanostructures in the micropores of PP membranes.The composite membranes displayed the similar proton conductivity behavior at 60?and 90%RH.Furthermore,the proton conductivity of PMAC11-IP6/PP at 190?was measured to be 3.19×10^-3 S/cm,demonstrating the capability of the membranes for high-temperature proton transport.