Formation and phase transition of the disordered Form I’ in electrospun PEO-thiourea complex nanofibers

Abstract A new crystal modification named as Form I’, a disordered counterpart of Form I, was for the first confirmed for the PEO (Poly (ethylene oxide))-thiourea complex nanofibers prepared by electrospinning technique. The Form I’ has the same thiourea molar fraction (0.4) as the Form I, but is more disordered and less thermally stable. During the heating process, an unexpected cold crystallization peak around 93.0 °C was observed for the Form I’ in the DSC heating scan. It arises from the phase transition from Form I’ to Form I. Temperature-dependent FTIR demonstrates that the Form I’ to Form I phase transformation undergoes a sequential process during the heating period.