The perspectives of application of nanocrystals for obtaining novel composite materials
Bogdan Pałosz Centrum Badań Wysokociśnieniowych PAN, ul. Sokołowska 29/37, 01-142 Warszawa
Annals 4 No. 9, 2004 pages 16-27
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abstract In the vast literature on composite materials one can find a number of definitions of the term „composite”. In the author’s opinion only the simplest one, i.e. „(...) composites are a nonhomogenous mixture of at least two permanently bound homogeneous phases (or materials).” [1], can be accepted without a doubt. Numerous attempts to improve this simple definition by its refinement or explanations [2, 3] results in its downgrading (the more additional comments, the less clear-cut the definition becomes), while the definition should serve as an unambiguous reference point and not as a subject of discussions. That comment is to address particularly the attempts to group separately composites containing nanocrystals, thus „nano-composites”. If we accepted some of the „refined” definitions of a composite we would have to admit that numerous nanocrystalline materials should be excluded from the class of composites. For example, an addition (to the definition of a composite) of a requirement that „there must exist a definite boundary between the components of a composite” leads to a discussion (more like a quarrel) on the methods that have to be used to observe the boundaries (optical microscope? SEM? TEM? AFM? ....?). Similarly, defining the function of the components or stating that „the properties of a composite are a function of the properties of its components and their content” does not explain anything and may only serve the purpose of excluding some materials from the class of composites. The intention of the author of this article is to turn the attention of the materials science community to some properties of nanocrystals which may be useful for obtaining composite materials with novel properties. The term „nanocrystal” itself is not unambiguously defined in the literature. That may lead to misunderstandings as to a justification of using this term both in the literature and in the research projects and programs. In this work we describe some selected physical properties specific to nanocrystals, with a particular reference to their atomic structure. We describe research problems that need to be solved to advance new (nano-)technologies which would take advantage of the unique properties of nanocrystals. Key words: nanocrystals, (nano?)composites, atomic structure, properties