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The fluorescence excitation and emission spectra of a liquid crystal E7 in ethanol have been explored at a variety of concentrations from very dilute solutions ( −7 mol/L) to concentrated solutions (>1.0×10 −2 mol/L) and also for neat E7. The result showed a strong dependence of the steady-state fluorescence behavior on E7 concentration in ethanol. The photophysical behavior has been interpreted in terms of short-range and long-range intermolecular interactions and ground-state molecular association as well as spectral changes of the fluorescence excitation and emission. The short-range intermolecular interaction characterized by the fluorescence emission band with the maximum between 376 and 385 nm gradually increases with increasing E7 concentration. On the other hand, the long-range intermolecular interaction characterized by the emission band with the maximum between 347 and 362 nm gradually decreases with increasing E7 concentration. Consequently, with increasing E7 concentration in ethanol the long-range interaction effect is reduced, whereas the short-range effect is enhanced and the monomer emission completely disappears at concentrations greater than 2.83×10 −5 mol/L.

This article reports on the dynamic mechanical and thermal properties of thermosetting phenylethynyl-terminated polyimide (PETI-5) composites reinforced with expanded graphite (EG) nanoplatelets having various average particle sizes and content. The EG nanoplatelets with varying particle sizes were prepared by different pulverization techniques through intercalation and exfoliation of natural graphite flakes. The effect of the EG particle size and concentration of the thermal behavior of PETI-5/EG composites was investigated with several thermal analysis methods (DMA, TMA, and DSC). The storage modulus dynamic mechanical properties and glass transition temperature significantly increased with increasing concentration of EG nanoreinforcements regardless of size. The coefficient of thermal expansion significantly decreased, especially in the glass transition region.

In the present study, the fluorescence behavior of a phenylethynyl-terminated imide (LaRC PETI-5) resin, a bismaleimide (BMI) resin, and various LaRC PETI-5/BMI blends with different blend compositions has been characterized as a function of heat-treatment temperature, using a steady-state fluorescence technique with a front-face illumination method for solid-state films. It is observed that there are distinguishable changes in the spectral shape, size, and position of fluorescence with varying heat-treatment temperature in the pure and blend samples. The result is qualitatively explained in terms of charge transfer complex formation as well as microenvironmental change with local mobility and viscosity occurring in the LaRC PETI-5, BMI, and their blends during the cure process. The result also implies that a steady-state fluorescence technique may be a useful tool to understand the processing conditions of polyimides and their blends in the film form on the basis of their thermo-photophysical responses.