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Exceptional Mechanical Properties (exceptional + mechanical_property)

Distribution by Scientific Domains

Polymers and Materials Science	50%

Selected Abstracts

Studying natural structural protein fibers by solid-state nuclear magnetic resonance

CONCEPTS IN MAGNETIC RESONANCE, Issue 1 2009
Alexandre A. Arnold
Abstract As a consequence of evolutionary pressure, various organisms have developed structural fibers displaying a range of exceptional mechanical properties adapted specifically to their functions. An understanding of these properties at the molecular level requires a detailed description of local structure, orientation with respect to the fiber and size of constitutive units, and dynamics on various timescales. The size and lack of long-range order in these protein systems constitute an important challenge to classical structural techniques such as high-resolution NMR and X-ray diffraction. Solid-state NMR overcomes these constraints and is uniquely suited to the study of these inherently disordered systems. Solid-state NMR experiments developed or applied to determine structure, orientation, and dynamics of these complex proteins will be reviewed and illustrated through examples of their applications to fibers such as spider and silkworm silks, collagen, elastin, and keratin. © 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part A 34A: 24,27, 2009. [source]

The life history of Salicaceae living in the active zone of floodplains

FRESHWATER BIOLOGY, Issue 4 2002
S. KARRENBERG
1.,Exposed riverine sediments are difficult substrata for seedling establishment because of extremes in the microclimate, poor soil conditions and frequent habitat turnover. Various species of willows and poplars (Salicaceae) appear to be particularly successful in colonising such sediments and are often dominant in floodplain habitats throughout the northern temperate zone. 2.,In many Salicaceae regeneration seems to be adapted to regular disturbance by flooding. Efficient seed dispersal is achieved by the production of abundant seed in spring and early summer, which are dispersed by air and water. Seeds are short-lived and germinate immediately on moist surfaces. Seedling establishment is only possible if these surfaces stay moist and undisturbed for a sufficient period of time. 3.,Larger plants of Salicaceae have exceptional mechanical properties, such as high bending stability, which enable them to withstand moderate floods. If uprooted, washed away or fragmented by more powerful floods these plants re-sprout vigorously. 4.,While these life characteristics can be interpreted as adaptations to the floodplain environment, they may also cause a high genetic variability in populations of Salicaceae and predispose Salicaceae to hybridization. Thus, a feed back between adaptive life history characteristics and the evolutionary process is proposed. [source]

Ultra Low- k Films Derived from Hyperbranched Polycarbosilanes (HBPCS),

ADVANCED FUNCTIONAL MATERIALS, Issue 24 2008
Jitendra S. Rathore
Abstract Dense and porous hyperbranched carbosiloxane thin films (HBCSO) are obtained by sol,gel processing using methylene-bridged hyperbranched polycarbosilanes (HBPCSs) with the general compositional formula {(OMe)2Si(CH2)}. Introduction of porosity is achieved using a porogen templating approach, allowing the control of the films' dielectric constant from 2.9 to as low as 1.8. Over the entire dielectric range, the HBCSO films exhibit exceptional mechanical properties, 2,3 times superior to those obtained for non-alkylene bridged organosiloxanes such as methylsilsesquioxanes (MSSQs) of similar densities and k -values. [source]

From carbon nanotube coatings to high-performance polymer nanocomposites

POLYMER INTERNATIONAL, Issue 4 2008
Stéphane Bredeau
Abstract Since their discovery at the beginning of the 1990s, carbon nanotubes (CNTs) have been the focus of considerable research by both academia and industry due to their remarkable and unique electronic and mechanical properties. Among numerous potential applications of CNTs, their use as reinforcing materials for polymers has recently received considerable attention since their exceptional mechanical properties, combined with their low density, offer tremendous opportunities for the development of fundamentally new material systems. However, the key challenge remains to reach a high level of nanoparticle dissociation (i.e. to break down the cohesion of aggregated CNTs) as well as a fine dispersion upon melt blending within the selected matrices. Therefore, this contribution aims at reviewing the exceptional efficiency of CNT coating by a thin layer of polymer as obtained by an in situ polymerization process catalysed directly from the nanofiller surface, known as the ,polymerization-filling technique'. This process allows for complete destructuring of the native filler aggregates. Interestingly enough, such surface-coated carbon nanotubes can be added as ,masterbatch' in commercial polymeric matrices leading to the production of polymer nanocomposites displaying much better thermomechanical, flame retardant and electrical conductive properties even at very low filler loading. Copyright © 2007 Society of Chemical Industry [source]