(529a) Creating a Ternary Phase Diagram for Pyrene and Its Oligomers: The Effect of Oligomeric Composition on Liquid Crystalline Phase Behavior

More than 50 years ago, Brooks and Taylor (B&T) at Union Carbide discovered that petroleum pitch forms a liquid crystalline phase, or mesophase, after proper annealing. This mesophase is a necessary precursor for graphite formation in petroleum pitch. Today, specialized mesophase pitches derived from petroleum can be graphitized to make carbon fibers with exceptional tensile modulus and thermal conductivity.

Ironically, since B&T’s discovery in 1965, our fundamental understanding of the role that molecular size, molecular structure, and mixture composition play in the properties of both the pitch precursor and the final carbon products continues to be quite limited. For example, the ideal molecular size for producing a mesophase pitch with a low melting point, a highly desirable property for processing, is unknown, as are the most desirable mixture compositions for forming low-melting mesophases.

Even with the recent significant advances in molecular characterization, the literally thousands of molecules present in petroleum pitches are a significant barrier to the development of structure–property relationships for pitches. To make the connection between molecular structure and final properties, we need a pitch system consisting of just a few components – with some of those components being isotropic and some being mesogenic.

We therefore propose the use of non-fragmenting pyrene oligomers, which are known to consist of both isotropic and mesogenic components. Although our group discovered that trimer forms 100% mesophase, here our interests lie with mixtures of these oligomers and their mesogeneity. To help us create these mixtures, we are using our unique supercritical extraction (SCE) column setup to isolate both pure pyrene oligomers and well-defined binary and ternary mixtures of said oligomers. This information will be used to generate one of the first true ternary phase diagrams of isotropic–mesophase behavior for a model system based on petroleum pitches.