The molecular scaling of raw pitches by oscillatory rheometry

Alpha relaxation and viscosity measurements performed above the glass trans ition region have been used for raw pitch molecular scale characterization. The characteristic time tau(proportional to) of the alpha relaxation is kn own to be similar to the molecular mobility characteristic time tau(m). Vis cosity-temperature and tau(m)-temperature data allow molecular equivalent h ydrodynamical diameter estimation through well known Stokes-Einstein relati ons. This procedure applied to two petroleum and two coal tar pitches led t o a 9.5-20 Angstrom hydrodynamical diameter range. Those results are in goo d agreement with basic structural units (BSU) theoretical molecular models or other experimental studies available in the literature. Pitch molecular scale seems similar to the coronene and ovalene monomers, dimers and trimer sizes. Moreover, an extrusion effect has been observed on coal tar pitch r esulting in a possible edge-to-edge orientation. A correlation between alph a, beta and gamma resins and BSU diameter range is proposed. (C) 1999 Elsev ier Science Ltd. All rights reserved.