Abstract
Thermodynamic glass transition processes of electrospun membranes were first introduced to study their dynamic relaxation nature, which is not constantly in equilibrium. The relaxation modes of electrospun membranes are slow but measurable near and above the Tg, given the stretched chain over long distances. Based on differential scanning calorimetry (DSC) experiments and the general principle of mode-coupling theory (MCT), endothermic peak temperature and relaxation enthalpy were used to analyze the relaxation process by capturing these instantaneous “arrested” structures. The short- and long-wavelength relaxation modes could be identified with different annealing times and temperatures relative to DSC-measured Tg for electrospun membranes with different molecular weights. Results clearly showed the dynamic nature of a glass transition in polymeric materials. Tp and enthalpy loss initially increased and then directly decreased with the increase in annealing time. When Ta > Tg, regardless of the size of the molecular weight, the Tp and enthalpy loss of the PLGA fibers would directly decrease, and the curves would shift toward the melted one. Combination of electrospinningand normal DSC instrument can be used to investigating the dynamic relax process through an adequately designed kinetic scanning procedure. This result can be explained by the general principle of MCT-type dynamic theory.
Highlights
Physical aging of glassy polymer materials, which is below their transition temperature [1] during storage and application, leads to changes in the electrical, thermal and mechanical properties [2–4]
To generate differential scanning calorimetry (DSC) curves reflecting chain lengths and segment mobilities, the relaxation process can be accelerated by increasing the annealing temperature
The PLGA electrospun fibrous membranes with three molecular weights and unique fiber diameters were used as a model system with regenerated films of the same compo sition
Summary
Physical aging of glassy polymer materials, which is below their transition temperature [1] during storage and application, leads to changes in the electrical, thermal and mechanical properties [2–4]. Any MCT theory for understanding the glass transition process includes Götze MCT [24] failed to provide detailed quantitative guidance for data analysis, multiple relaxation times are essential. According to the general principle of MCT, extensive relaxation times slow down non proportionally at temperatures lower than the DSC Tg. any MCT theory for understanding the glass transition process includes Götze MCT [24] failed to provide detailed quantitative guidance for data analysis, multiple relaxation times are essential. Through this study, instantaneous structures during the DSC measurements over different annealing times and temperatures can be obtained to understand better the dynamic nature of glass transition and a favorable control of its structure/morphology during manufacturing, storage, and shape memory function delivery in the application.
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