Mechanical Properties of a Nanostructured Poly (KAMPS)/aragonite Composite Chad S. Korach Department of Mechanical Engineering, Stony Brook University, Stony Brook, NY, 11794, USA Ranjith Krishna Pai Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973, USA International Iberian Nanotechnology Laboratory, 4715-310 Braga, Portugal ABSTRACT The mechanical properties of a new poly(KAMPS)/aragonite composite are investigated. The composite is fabricated using biomimetic pathways and formed entirely from dilute aqueous solutions. Nanorods of aragonite are formed within a matrix of poly(KAMPS)-based polyelectrolyte and a nanostructred material with rod widths of 120nm and polymer-filled spacings of 10-20nm is created. Nanoindentation is used to measure mechanical properties of the composite material. The elastic modulus of 44GPa and hardness of 2.8GPa are found similar to that of nacre and exhibit a hardening mechanism at the nanoscale. The new biomimetic composite has application in the biomedical and dental fields. 1. Introduction Well-controlled nanostructures obtained via polymer-mediated synthesis have generated considerable scientific and technological interest.[1] The ability to control the nucleation and growth of hierarchical structures often leads to fascinating shapes combined with remarkable mechanical properties but requires a high level of control over structure, size, morphology, and orientation by assembly at organic surfaces.[2] Calcium carbonate (CaCO3) is one of the most studied systems for its pivotal role in understanding the natural mechanism of biomineralization and for designing new biomimetic composite materials[3,4]. A classic and widely studied [5-10] example of a biocomposite is the nacre of abalone shell, composed of hexagonal platelets of aragonite (a polymorph of CaCO3), 10-20 μm wide and, 0.2-0.9 μm thick, arranged in a continuous, parallel lamina. These layers are separated by sheets of organic matrix (10-50 nm thick) composed of elastic biopolymers such as chitin, lustrin and silk-like proteins [11]. This mixture of brittle platelets and thin layers of elastic biopolymers make the material strong [12] and resilient (shock absorbent). Strength and resilience are also likely to be due to adhesion by the “brickwork” arrangement of the platelets, which inhibits transverse crack propagation. This design at multiple length scales increases its hardness enormously, making the biocomposite similar to that of silicon [13]. The intimate association of organic/inorganic materials of nacre and its structure-function relationship has inspired a large class of biomimetic-advanced materials.[14] The addition of organic polymers to inorganic components markedly improves the ability to absorb energy during deformation of composites.[15] Traditional ceramics are brittle, and have been improved upon with new ideas such as reversible toughening mechanisms, and large fracture tolerance,[16,17] leading to the development of ceramics with an order larger toughness. The toughness of these materials though remains lower than that of steel. Studying the materiomics of natural biocomposites may create the ability to, by mimicking their nanostructuring and mechanisms, fabricate ceramics that are 50 times tougher.[18,19] Biomimetic strategies have been proposed to develop materials with mechanical characteristics similar to nacre [20-26], and there have been many materials fabricated to either mimic nacre or to mimic the mechanisms of nacre to create toughening. A comprehensive review can be found in [27]. However, none of them can truly recreate the similar aragonite ‘bricks’ with the remarkable mechanism of platelet sliding, because most conventional processing techniques simply do not offer the nanoscale level of control needed to create a highly regular bricks-and-mortar-type arrangements. Biomimicry of the toughening mechanism of nacre has been performed at larger scales where control of the processing proves simpler, and has demonstrated successfully the toughening. Here, a simple, economic, and one step strategy to engineer polyelectrolyte-based composite materials that mimics both nanoscale structural and mechanical properties of nacre is introduced. Previously, it was found that on the molecular level, calcium-mediated sacrificial bonds increase stiffness and enhance energy dissipation in bone. [28] The ability of a polymeric component to infer a large fracture or adhesion energy is related to the bonding to the more rigid components and the ability to sustain a significant elongation without complete breakage. Among the various kinds of polymeric components employed as adhesion based-assembly in bioinspired morphosynthesis, 2acrylamido-2-methyl-1-propane sulfonic acid (AMPS) based polyelectrolyte is considered to be extraordinarily effective. T. Proulx (ed.), Mechanics of Biological Systems and Materials, Volume 2, Conference Proceedings of the Society for Experimental Mechanics Series 9999, DOI 10.1007/978-1-4614-0219-0_18, © The Society for Experimental Mechanics, Inc. 2011 131
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