Real-time monitoring of molecular dynamics of ethylene glycol dimethacrylate glass former

The isothermal cold-crystallization of the glass-former low-molecular-weight compound, ethylene glycol dimethacrylate (EGDMA), was monitored by real-time dielectric relaxation spectroscopy (DRS) and differential scanning calorimetry (DSC). The α-relaxation associated with the dynamic glass transition as detected by DRS was followed at different crystallization temperatures, T<sub>cr</sub>, nearly above the glass transition temperature, 176 K (1.06 ≤ T<sub>cr</sub>/<sub>Tg</sub> ≤ 1.12). It was found that the α-process depletes upon cold-crystallization with no significant changes in either shape or location. At advanced crystallization states, a new relaxation, α′-process, evolves that was assigned to the mobility of molecules lying adjacent to crystalline surfaces. From the time evolution of the normalized permittivity, it was possible to get kinetic information that was complemented with the calorimetric data. From DSC measurements that were also carried out under melt-crystallization, an enlarged temperature range was covered (up to T<sub>cr</sub>/T<sub>g</sub> = 1.24), allowing us to draw a diagram of time−temperature crystallization for this system. Dielectric relaxation spectroscopy proved to be a sensitive tool to probe the mobility in the remaining amorphous regions even at high crystallinities

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 α-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