Rheology of supercooled P-Se glass-forming liquids: From networks to molecules and the emergence of power-law relaxation behavior

摘要

The effect of the network-to-molecular structural transformation with increasing phosphorus content in PxSe100-x (30 = 63, on the other hand, are characterized by a departure from Maxwell behavior as the storage modulus shows a linear frequency scaling G'(omega) similar to omega over nearly the entire frequency range below the G'-G " crossover and a nearly constant ratio of G "/G' in the terminal region. Moreover, the dynamic viscosity of these rather fragile molecular liquids shows significant enhancement over that of network liquids at frequencies below the dynamical onset and does not reach a frequency-independent regime even at frequencies that are four orders of magnitude lower than that of the onset. Such power-law relaxation behavior of the molecular liquids is ascribed to an extremely broad distribution of relaxation timescales with the coexistence of rapid rotational motion of individual molecules and cooperative dynamics of transient molecular clusters, with the latter being significantly slower than the shear relaxation timescale. Published under an exclusive license by AIP Publishing.