Fracture nanostructures

The development of polymerizable microemulsions consisting of only three basic components (except a water component) for producing transparent solid polymers with nanostructure is a recent achievement [87]. For example. Fig. 5 shows the SEM micrograph of the fractured polymer prepared by the UV-initiated polymerization of a bicontinuous microemulsion consisting of 35 wt% water, 35 wt% AUDMAA and 30 wt% MMA. This micrograph reveals randomly distributed bicontinuous nanostructures of water channels and polymer domains. The widths of the bicontinuous nanostructures were about 40-60 nm. The sizes of the nanostructures can be readily reduced by adding 2-hydro-... 

We have shown that strength and stability can be obtained under selected conditions in nanostructured and dispersion reinforced systems. However, for structural applications, a balance of properties is critical - fracture and fatigue behavior of these systems are not well-established. Processing scale-up is another big challenge in these systems most of the properties have been demonstrated on laboratory-scale materials. Process scale-up is required to produce useful quantities of materials for sub-scale component demonstration as well as design property evaluation. The retention of useful microstructures, microstructural homogeneity as well as critical material properties has to be demonstrated in scaled-up materials. While our focus has been on structural applications, there may be other non-structural or functional applications for these systems. Future investigations will be focused on such opportunities. 

Referring to microbial cellulose applications, bacterial nanocellulose has proven to be a remarkably versatile biomaterial with use in paper products, electronics, acoustic membranes, reinforcement of composite materials, membrane filters, hydraulic fracturing fluids, edible food packaging films, and due to its unique nanostructure and properties, in numerous medical and tissue-engineered applications (tissue-engineered constructs, wound healing devices, etc). 

Clearly, like Young s modulus, hardness decreases rapidly with increasing porosity. Polymer-porous silicon composites (see handbook chapters Porous Silicon-Polymer Composites and Porous Silicon and Conductive Polymer Nanostructures via Templating ) are likely to have very low hardness but potentially high fracture toughness (see next section). 

Peterson KE (1982) Silicon as a mechanical material. Proc IEEE 70(5) 420 Phalippou J et al (1989) Fracture toughness of silica aerogels. Revue De Phys Appl C4(24) 191-196 Populaire CH et al (2003) On mechanical properties of nanostructured mesoporous silicon. Appl Phys Lett 83 1370... 

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