Nanostructured Ultrastrong Materials
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The mass–strength ratio is of exceptional importance for different applications. Critical parts of various moving vehicles from satellites to aircrafts to cars depend on strength and toughness of the materials they are made of, while strict limitations on the weight of the different components are placed by the launch technology. Single-walled carbon nanotubes (SWNT) present significant potential as the basic material for space applications. The exceptional mechanical properties of SWNTs have prompted intensive studies of their composites. These qualities can also be used in a variety of other technologies from automotive to military and medical. However, the present composites have shown only a moderate strength enhancement when compared to other hybrid materials. Although substantial advances have been made, the mechanical characteristics of SWNT-doped polymers are noticeably below their highly anticipated potential. Pristine SWNTs are well known for poor solubilization, which leads to phase segregation of composites. Severe structural inhomogeneities result in the premature failure of the hybrid SWNT–polymer materials. The connectivity with and uniform distribution within the matrix are essential structural requirements for the strong SWNT composites. Here we show that a new processing approach based on sequential layering of chemically modified nanotubes and polyelectrolytes can greatly diminish the phase segregation and render SWNT composite highly homogeneous. Combined with chemical cross-linking, this processing leads to drastically improved mechanical properties. The tensile strength of the composites is several times higher than that of SWNT composites made via mixing; it approaches values seen for hard ceramics. The universality of the layering approach applicable to a wide range of functional materials makes possible successful incorporation of SWNT into a variety of composites, imparting them required mechanical properties.
The thin-film membranes that are obtained as a result of the layer-by-layer process can be used as an intermediate or as a component of ultrastrong laminates. At the same time, the prepared membranes can also be utilized in the as-prepared form for space and biomedical technologies because of the combined strength and multiple functionalities of the SWNT membranes.