Mechanically strong and highly ion conductive graphene oxide liquid crystal film containing the poly(amic acid) salt

Abstract

Graphene oxide (GO) sheets can be aligned at low concentration to form a liquid crystal phase. Intriguingly, the poly(amic acid) salt (PAAS) can be used as an intercalated polymer in GO liquid crystal film. The PAAS is intercalated into the aligned GO sheets, increasing water absorbing capacity and reformatting hydrogen bonds in the GO. The suspensions for each content, observed by polarizing microscope, revealed a lyotropic liquid crystal nematic dispersion, even after PAAS was added. The mechanical strength of the GO films was improved by hydrogen bonding between the PAAS and GO sheets. The ultimate tensile strength (181 MPa) and modulus (222 MPa) of the reinforced film are tougher than pristine GO film, respectively. As such, interactions through the plane between the GO sheets and PAAS also improved the films' mechanical stability at high humidity. Functional groups of PAAS also improved the water absorbing capacity and flexibility of the water channels, improving ionic conductivity (0.67 S/cm). This is extraordinary to achieve high ionic conductivity by maintaining tensile strength. Therefore, GO/PAAS films are readily applicable for battery separator and fuel cell membranes. High tensile strength can prevent internal short circuit effectively only with 5 to 10 mu m of thickness. Highlights We introduce the poly(amic acid) salt as an intercalated polymer in graphene oxide liquid crystal film. poly(amic acid) salt can increase water absorbing capacity and reformat hydrogen bonds in the graphene oxide. The mechanical strength of the graphene oxide films was improved by hydrogen bonding between the PAAS and graphene oxide sheets. Increased water absorbing capacity and flexibility of the water channels improved ionic conductivity (0.67 S/cm).