One of the applications of nanomaterials is as reinforcements in composites, wherein small additions of nanomaterials lead to large enhancements in mechanical properties. There have been extensive studies in the literature on composites where a polymer matrix is reinforced by a single nanomaterial such as carbon nanotubes. In this article, we examine the significant synergistic effects observed when 2 different types of nanocarbons are incorporated in a polymer matrix. Thus, binary combinations of nanodiamond, fewlayer graphene, and single-walled nanotubes have been used to reinforce polyvinyl alcohol. The mechanical properties of the resulting composites, evaluated by the nanoindentation technique, show extraordinary synergy, improving the stiffness and hardness by as much as 400% compared to those obtained with single nanocarbon reinforcements. These results suggest a way of designing advanced materials with extraordinary mechanical properties by incorporating small amounts of 2 nanomaterials such as graphene plus nanodiamond or nanodiamond plus carbon nanotube.binary combinations ͉ nanoindentation technique ͉ polyvinyl alcohol ͉ synergistic effects A mong the many unique attributes of nanomaterials, especially noteworthy are their large surface to volume ratios and outstanding mechanical properties. These properties offer venues for exciting areas of research as well as for technological innovations. Thus, an important use of nanomaterials is in reinforcing polymer matrices taking advantage of the ultra-high stiffness and hardness exhibited by them. Recent research has shown that small additions (up to Ϸ1 wt%) of certain nanomaterials such as carbon nanaotubes enhance the mechanical properties markedly, sometimes by as much as 100% (1-8). Although the precise mechanism responsible for this dramatic enhancement is not entirely understood, it is generally believed that molecular level interactions between the nanomaterials and polymer matrices play a major role. The large interface area available for such interactions clearly hold the key for the dramatic enhancement in mechanical properties.Of the variety of nanomaterials synthesized and characterized in recent years, nanocarbons of different dimentionalities are of particular interest, as exemplified by nanodiamond, nanotubes and graphene with dimensionalities of 0, 1, and 2, respectively (1-3). Extensive research has been carried out on the mechanical properties of composites made of polymer matrices with 1 of the nanocarbons as the reinforcement phase (1-8). We would expect the nature of interaction of the nanocarbon constituent with the matrix to vary with the dimensionality. For example, carbon nanotubes added to a polymer can interact over the length of the polymer chain whereas a nanodiamond particle can interact only at a point, possibly at the ends of a polymer chain. While each of the nanocarbons improves the mechanical properties of the polymer matrix, we felt intuitively that incorporation of 2 nanocarbons could lead to synergistic effects in the m...

The mechanical properties of polyvinyl alcohol (PVA) and poly(methyl methacrylate) (PMMA)-matrix composites reinforced by functionalized few-layer graphene (FG) have been evaluated using the nano-indentation technique. A significant increase in both the elastic modulus and hardness is observed with the addition of 0.6 wt% of graphene. The crystallinity of PVA also increases with the addition of FG. This and the good mechanical interaction between the polymer and the FG, which provides better load transfer between the matrix and the fiber, are suggested to be responsible for the observed improvement in mechanical properties of the polymers.

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