DWI at RWTH Aachen University - Institute for Interactive Materials Research, Forckenbeckstr. 50, D-52056 Aachen, Germany.
Nanoscale. 2013 Oct 7;5(19):9348-56. doi: 10.1039/c3nr02983b. Epub 2013 Aug 19.
Although tremendous effort has been focused on enhancing the mechanical properties of nacre-mimetic materials, conservation of high stiffness and strength against hydration-induced decay of mechanical properties at high humidity remains a fundamental challenge in such water-borne high-performance materials. Herein, we demonstrate that ionic supramolecular bonds, introduced by infiltration of divalent Cu(2+) ions, allow efficient stabilization of the mechanical properties of self-assembled water-borne nacre-mimetics based on sustainable sodium carboxymethylcellulose (Na(+)CMC) and natural sodium montmorillonite nanoclay (Na(+)MTM) against high humidity (95% RH). The mechanical properties in the highly hydrated state (Young's modulus up to 13.5 GPa and tensile strength up to 125 MPa) are in fact comparable to a range of non-crosslinked nacre-mimetic materials in the dry state. Moreover, the Cu(2+)-treated nacre-inspired materials display synergetic mechanical properties as found in a simultaneous improvement of stiffness, strength and toughness, as compared to the pristine material. Significant inelastic deformation takes place considering the highly reinforced state. This contrasts the typical behaviour of tight, covalent crosslinks and is suggested to originate from a sacrificial, dynamic breakage and rebinding of transient supramolecular ionic bonds. Considering easy access to a large range of ionic interactions and alteration of counter-ion charge via external stimuli, we foresee responsive and adaptive mechanical properties in highly reinforced and stiff bio-inspired bulk nanocomposites and in other bio-inspired materials, e.g. nanocellulose papers and peptide-based materials.
尽管人们已经投入了大量的努力来提高珍珠层仿生材料的机械性能，但在高湿度下保持高刚度和强度，同时防止机械性能因水合作用而下降，仍然是这类水性高性能材料的一个基本挑战。在这里，我们证明了通过渗透二价 Cu(2+)离子引入的离子超分子键，可以有效地稳定基于可持续的羧甲基纤维素钠（Na(+)CMC）和天然蒙脱土纳米粘土（Na(+)MTM）的自组装水性珍珠层仿生材料的机械性能，使其在高湿度（95%RH）下具有良好的稳定性。在高度水合状态下的机械性能（杨氏模量高达 13.5 GPa，拉伸强度高达 125 MPa）实际上与一系列非交联的珍珠层仿生材料在干燥状态下的性能相当。此外，与原始材料相比，经过 Cu(2+)处理的仿生珍珠层材料表现出协同的机械性能，表现为刚度、强度和韧性的同时提高。考虑到高度增强的状态，会发生显著的非弹性变形。这与紧密的、共价交联的典型行为形成对比，据推测，这源于瞬时超分子离子键的牺牲性、动态断裂和重新结合。考虑到可以方便地获得广泛的离子相互作用，并通过外部刺激改变抗衡离子的电荷，我们预计在高度增强和刚性的仿生块状纳米复合材料以及其他仿生材料（例如纳米纤维素纸和基于肽的材料）中会具有响应性和适应性的机械性能。
