Mapping the Mechanical Properties of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Banded Spherulites by Nanoindentation

Nanoindentation provides clear evidence that spherulite banding can be associated with a continuous modulation of mechanical properties from the more compliant peaks to the stiffer valleys. The structural arrangement in polymer-banded spherulites has intrigued scientists for many decades, and the debate has been recently intensified with the advent of new experimental evidence. The present paper approaches this issue by exploring the local mechanical properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-ringed spherulites via nanoindentation and discussing the confidence of the results. It was found that storage modulus and hardness across the banding morphology can be described as a sequence of regular oscillations with a periodicity that exactly matches the one observed using optical and atomic force microscopy. Results are consistent with the model of regular twisting of the lamellae, with flat-on arrangement in the low regions and edge-on lamellae in the crests.The authors wish to thank the MINECO (Ministerio de Economía y Competitividad), Spain, for funding the research reported under grants MAT2013-47898-C2-1-R (covering the costs to publish in open access) and MAT2012-36341. Patricia Enrique-Jimenez acknowledges MINECO for a FPI (Formación Personal Investigador) studentship. We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)