Characteristic exothermic behavior and short-range ordering in aggregates of ultimately fine fibers made of monodisperse polystyrene

Abstract

We investigated the thermal behavior and structure formation of electrospun (ES) fiber mats and freeze-dried (FD) foams consisting of very fine fibrous network structure, and compared the results with those of self-standing membranes, in which the motion of boundary molecules is not restrained by contacting solids. We chose monodisperse polystyrene (PS) as a material polymer to examine the molecular weight effect as well. For the ES fibers and FD foams, a characteristic exothermic peak was observed at around 110 °C in DSC curve at 1st scan, while such exothermic peak did not appear for the self-standing films and bulk. To further investigate the nano-periodic structure inside materials during heating, we carried out WAXD measurements. Although the PS used in this study was atactic, the ES fibers formed ordered structure near its glass-transition temperature (Tg). Furthermore, the FD foams exhibited high short-range order even in the unheated state, and the regularity was more developed by heating above 120 °C.