Molecular dynamics of ethylene glycol dimethacrylate glass former: influence of different crystallization pathways

The crystallization induced by different thermal treatments of a low molecular weight glass former, ethylene glycol dimethacrylate (EGDMA), was investigated by dielectric relaxation spectroscopy (DRS) and differential scanning calorimetry (DSC). The fully amorphous material, dielectrically characterized for the first time, exhibits three relaxation processes: the a-relaxation related to dynamic glass transition whose relaxation rate obeys a Vogel-Fulcher-Tamman-Hesse (VFTH) law and two secondary processes (β and γ) with Arrhenius temperature dependence. Therefore, the evaluation of distinct crystallization pathways driven by different thermal histories was accomplished by monitoring the mobility changes in the multiple dielectric relaxation processes. Besides isothermal cold-crystallization, nonisothermal crystallizations coming from both the melt and the glassy states were induced. While an amorphous fraction, characterized by a glass transition, remains subsequent to crystallization from the melt, no α-relaxation is detected after the material undergoes nonisothermal cold-crystallization. In the latter, the secondary relaxations persist with a new process that evolves at low frequencies, designated as α' that was also detected at advanced crystallization states under isothermal cold-crystallization. Under the depletion of the α-relaxation, the β-process when detected becomes better resolved keeping the same location prior to crystallization leading to a decoupled temperature dependence relative to the α-process.