Novel method for fast scanning calorimetry of electrospun fibers

Abstract

© 2018 Elsevier B.V. Fast scanning chip-based calorimetry allows for the study of challenging polymers, for example, those which have rapid nucleation and crystallization kinetics, or which degrade within their melting range. Heating rates up to 4000 K/s allow for studies of hetero- and homogeneous nucleation at time scales inaccessible with conventional calorimeters, whose rates are typically less than about 0.5 K/s. Recent studies have successfully demonstrated methodologies for obtaining quantitative measurements of thermal properties of polymer samples using fast scanning calorimetry (FSC). However, these studies have been restricted to thin films or small flakes cut from bulk samples. Fibrous samples present extreme challenges due to their fluffy nature, which prevents good thermal contact for FSC. Here we present a new methodology to obtain quantitative fast scanning thermal data from electrospun nanofibers using the Mettler Flash DSC1. The technique is demonstrated using polyethylene terephthalate (PET) whose fundamental thermal properties are available in the literature, and provide a good test for the accuracy of FSC on micron- to nano-scale fibers. The structure of nanofibers requires special methods to load nanogram-sized samples onto a UFSC1 sensor. Fibers were directly spun onto copper TEM grids which provide a durable substrate to support bundles of nanofibers and possess excellent thermal conductivity allowing for a strong, repeatable signal and ensure good sample-to-sensor contact. As spun amorphous samples were held isothermally at temperatures ranging from Tg (69 °C) to Tm (280 °C) then heated at 2000 K/s to assess their melting behavior after cold crystallization. Results show that this sample preparation technique provides quantitative data, comparing favorably to that achieved with conventional calorimeters.