Electrospun Fibrous Membrane with Confined Chain Configuration: Dynamic Relaxation and Glass Transition

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 T-g,T- 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 T-g for electrospun membranes with different molecular weights. Results clearly showed the dynamic nature of a glass transition in polymeric materials. T-p and enthalpy loss initially increased and then directly decreased with the increase in annealing time. When T-a > T-g, regardless of the size of the molecular weight, the T-p 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.