Can Nature’s Design be Improved Upon? High Strength, Transparent Nacre-Like Nanocomposites with Double Network of Sacrificial Cross Links

Abstract

The preparation of a high-strength and highly transparent nacre-like nanocomposite via layer-by-layer assembly technique from poly(vinyl alcohol) (PVA) and Na+-montmorillonite clay nanosheets is reported in this article. We show that a high density of weak bonding interactions between the polymer and the clay particles: hydrogen, dipole-induced dipole, and van der Waals undergoing break-reform deformations, can lead to high strength nanocomposites: sigmaUTS approximately 150 MPa and E' approximately 13 GPa. Further introduction of ionic bonds into the polymeric matrix creates a double network of sacrificial bonds which dramatically increases the mechanical properties: sigmaUTS approximately 320 MPa and E' approximately 60 GPa.

Nacre-mimetics with synthetic nanoclays up to ultrahigh aspect ratios

“…Most importantly, the ultrahigh aspect ratio of NTS allows reaching stiffness values significantly higher than what can be achieved with natural MTM. PVA/NTS in fact realizes values that have previously only been achievable using covalent 36,62 or supramolecular crosslinking 15,40 . Hence, there is a clear and profound advantage of exploiting larger aspect ratio nanoclays, giving a fresh impulse for the proper selection in future nacremimetics.…”

“…This yields very well-defined core/shell particles without excess of polymer and allows to approach highly ordered nacre-mimetics with fully exfoliated synthetic nanoclays at biomimetic compositions. We use PVA because of its known affinity to nanoclays and also because a comparison can be made to earlier nacre-mimetics, either prepared by the layer-by-layer technique or via selfassembly 10,15,36,40,45 . Table 1 gives an overview of the used nanoclays.…”

“…However, this is a major scientific and technological challenge as precise nanostructuration at such biomimetic compositions with high fractions of reinforcements is hard to combine with large-scale processing methods. Various efforts have been undertaken to mimic the layered hard/soft composite structure of nacre 9 via for example, several sequential approaches, such as LbL [10][11][12][13][14][15][16][17][18] and other multilayer deposition strategies 19,20 , ice-templating and sintering of ceramics [21][22][23] , spray coating 24,25 , glow discharge plasma deposition 26 , uncontrolled co-casting of polymer/clay mixtures 27,28 , or processes at interfaces 29,30 . Unfortunately, many of these approaches are limited to a very small scale, and remain technologically infeasible owing to energy-intensive and laborious multistep procedures.…”

Deoxyguanosine Phosphate Mediated Sacrificial Bonds Promote Synergistic Mechanical Properties in Nacre-Mimetic Nanocomposites

“…[17][18][19] The nacre-like complexity is difficult to transfer into synthetic materials to reproduce the mechanical behavior, as the highly ordered self-assembled structure and supramolecular interactions need to be mimicked at several length scales. Nacre has been mimicked by sequential deposition processes, [20][21][22][23][24][25] which are, however, not scalable and which are prohibitive when macroscale sample thicknesses are aimed. Ice-templating and sintering allows tough nacremimics but suffer from a multistep process.…”

Biomimetic design of materials and biomaterials inspired by the structure of nacre

“…For example, the build-up of a 100-bilayer film with a thickness of approximately 330 nm needs less than 1 hour, which is 20 times faster than dip-coating processes with the same characteristics. Another approach to the layer-by-layer assembly technique was that from Podsiadlo et al (2008), in which high-strength and highly transparent nacre-like nanocomposites with poly(vinyl alcohol) and Na C -MMT clay nanosheets were prepared. The formation of a high density of weak bonding interactions between the polymer and the clay particles can lead to high-strength nanocomposites.…”