Nanoclay-reinforced Polyacrylamide Composite: Synthesis, Structural and Mechanical Characterization
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Nanoclay-Reinforced Polyacrylamide Composite: Synthesis, Structural and Mechanical Characterization Yong Sun1, Zaiwang Huang1 and Xiaodong Li1,* 1 Department of Mechanical Engineering, University of South Carolina, 300 Main Street, Columbia, SC 29208, USA *[email protected] ABSTRACT A facile electrophoretic deposition method was successfully applied to achieve novel nanoclay-reinforced polyacrylamide nanocomposite thin films. A special curled architecture of the re-aggregated nanoclay-platelets was identified, providing a possible source for realizing the interlocking mechanism in the nanocomposites. The curled architecture could be the result from strain releasing when the thin films were peeled off from the substrates. Through micro-/nanoindentation and in situ observation of the deformation during tensile test with an atomic force microscope (AFM), the localized deformation mechanism of the synthesized materials was investigated in further details. The results implied that a localized crack diversion mechanism worked in the synthesized nanocomposite thin films, which resembled its nature counterpartnacre. The deformation behavior and fracture mechanism were discussed with reference to lamellar structure, interfacial strength between the nanoclays and the polyacrylamide matrix, and nanoclay agglomeration. INTRODUCTION Considering its spectacular mechanical properties, nacre (mother-of-pearl) is one of the most amazing masterpieces created by Mother Nature. With approximately 95% brittle inorganic aragonite (a mineral form of CaCO3) and a few percent of soft inorganic biopolymer, Mother Nature somehow is able to create a combination of ultra-high strength, and super-high toughness. The key to the “magic” is known as the brick-and-mortar arrangement. It bypasses the weakness of each component by integrating platelet-like ceramic building blocks with a biopolymer layer between the blocks to render hybrid materials [1-3]. Furthermore, individual aragonite platelet is composed of numerous nanoparticles with an average size of approximately 32-44 nm. The surprising fact is recently revealed by atomic force microscopy (AFM) observation and highresolution transmission electron microscopy (HRTEM) study. Such self-assembled architecture results in 2-fold increase in strength and a 1000-fold increase in toughness comparing to the constituted materials [4-5]. Generally speaking, it exhibits a ductile rather than brittle characteristic and hence improves the overall robustness of the structure. Now the problem is this, “what are the mechanisms that link the exquisite structure and the fascinating mechanical behavior”? Intensive studies and substantial progress have been made on the topic, in order to comprehend, and finally, to mimic the secret recipe [1-5]. A number of different materials have been selected as reinforcing platelets to manufacture polymer-matrix artificial composites, such as graphite, SiC and montmorillonite (MMT) clays [6-7], etc. Various routines of fabrication have been proposed, including l
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