Controlling the Properties of a Liquid Crystalline Epoxy Though Magnetic Field Processing

Abstract : It has been demonstrated recently that the physical and mechanical properties of liquid crystalline thermosets can be altered via processing in a magnetic field. Magnetic field processing imparts a degree of macromolecular anisotropy on the material. This anisotropy has been shown to cause a favorable change in some of these mechanical and physical properties. However, the degree of control over these property changes has yet to be studied in depth. The focus of this research is to explore the effects of the processing variables and determine the amount of control that exists over the final properties of the material. A liquid crystalline epoxy, 4, 4'-diglycidyloxy-alpha-methylstilbene, and tetrafunctional diamine crosslinking agent, sulfanilamide, were used as the resin system for this study. The process variables that were determined to be the largest effectors of the reorientation process are the magnetic field strength, the time in the field, and the amount of b-staging, or precuring, of the material. The response variable chosen to be studied was the second moment of the orientation function, or orientation parameter, determined by wide angle x-ray scattering (WAXS). A statistical experimental design was employed using CARD(registered) (Computer Aided Research and Development) software to investigate the interaction effects of the variables. The design used was a modified fractional factorial design to reduce the total number of samples required but still included several pairs of replicates to determine the experimental error not associated with the variation of the variables described above. The samples were prepared and cured in a magnetic field at the National High Magnetic Field Laboratory. Wide angle x-ray scattering (WAXS) experiments were conducted to determine the amount of orientation imparted in the samples. The orientation parameter calculated was used as the response variable for the statistical experimental design.