(72e) Nanoscale Structure-Property Relationships of Polyacrylonitrile/CNT Composites As a Function of Polymer Crystallinity and CNT Diameter

Polyacrylonitrile (PAN)/carbon nanotube (CNT) composites are used as precursors for ultrastrong and lightweight carbon fibers. This contribution presents insights into the structure at the atomic scale and the relationships to mechanical and thermal properties for different degrees of PAN preorientation and CNT diameter based on experimental data and molecular dynamics simulation. The inclusion of CNTs in the polymer matrix is favored for an intermediate degree of PAN orientation and small CNT diameter whereas high PAN crystallinity and larger CNT diameter disfavor CNT inclusion. We find that glass transition temperatures in composites are predictable with +/-5 K accuracy by simulations and correlate with the amount of CNT/polymer interfacial area per unit volume. I.e., an increase in Tg is observed in the presence of CNTs, for higher CNT volume fraction, and a decrease in Tg with larger CNT diameter at the same volume fraction. Changes in interfacial shear strength as a function of CNT characteristics and polymer crystallinity are explained and correlate with measurements for nanoscale/microscale domains.