Influence of Size and H-bonding on the Elasto-Plastic Mechanical Behavior of PVP–TA Nanofibers

Abstract

Developing advanced structural polymers with simultaneously high strength and toughness remains a significant materials design challenge. Two strategies that have been used in different polymers to address this challenge are dynamically cross-linking polymer chains through hydrogen bonds (H-bonds) and reducing the dimensions of polymeric structures to submicron length scales (i.e., size effects). The current study aims to understand the direct role of relatively weak H-bonds in improving the elasto-plastic mechanical properties of the much stronger glassy state polymers, which remains unclear in the existing literature. At the same time, the potential to combine H-bonding and size effects to synergistically achieve greater improvements in strength and toughness will be studied in this work. To this goal the large deformation elasto-plastic deformation response of single poly(vinylpyrrolidone)–tannic acid (PVP–TA) nanofibers of varying fiber diameters and TA concentrations (i.e., H-bonding) were characterized through submicron-scale tensile experiments. The results indicated that H-bonding was capable of directly and significantly improving the mechanical behavior of glassy PVP. H-bonding and size effects were found to affect the elastic and plastic properties differently. While these two effects were synergistic in the elastic regime, their interaction was more complex in the plastic deformation regime in general and for the thinnest fibers in particular. These observations provide useful insights into the design of improved H-bonded polymers for small-scale multifunctional applications.