LAUSR

While there is great interest in polymer nanofibers due to their high strength, methods to measure their time-temperature superposition (TTS) curves are lacking. The objective of this work is to demonstrate one such method and thereby to predict room temperature creep compliance over many decades of time. A complimentary measurement is also presented to estimate the associated activation energy. The experimental method is demonstrated for polyacrylonitrile (PAN) nanofibers using an on-chip surface micromachined stepper motor actuator. It is first shown that the method yields good agreement with previous room temperature measurements. Subsequently, data up to 95 °C, near the glass transition temperature, is presented. Time-temperature superposition master curves are then constructed, and activation energies for two narrow diameter ranges (221 ± 27 nm and 150 ± 9 nm) are determined. The activation energy of the 221 nm fiber agrees well with the bulk PAN value, while the 150 nm fiber is 50% larger, indicating the importance of higher chain packing and reduced chain mobility in thinner fibers. TTS curves spanning 7 (221 nm) and 9 (150 nm) decades are presented. Over this time span the creep compliance increases by a factor of approximately 10 for each. This work demonstrates a viable method to measure polymer nanofiber TTS curves from which quantitative activation energy can be determined, and from which creep compliance values over time can be predicted.