The capillary flow instability resulting in extrudate distortion has been studied for ethylene polymer melts using a molecular structure approach. It is found that the instability initiates at a critical value of elastic strain energy independent of (average) molecular weight for linear polyethylene. Once the flow breaks down, a slip interface within the melt is formed near the capillary wall, causing an abrupt increase in volumetric throughput. The velocity gradient within the melt remains continuous through the instability, however. Low molecular weight species present in the molecular weight distribution of linear polyethylene tend to suppress slip. Blends of linear and branched polyethylene exhibit instability behavior characteristic of both components throughout the entire range of composition. Results are discussed in terms of specific molecular mechanisms.

One of the most promising materials for fabricating cold cathodes for next generation high-performance flat panel devices is carbon nanotubes (CNTs). For this purpose, CNTs grown on metallic substrates are used to minimize contact resistance. In this report, we compare properties and field emission performance of CNTs grown via water assisted chemical vapor deposition using Inconel vs silicon (Si) substrates. Carbon nanotube forests grown on Inconel substrates are superior to the ones grown on silicon; low turn-on fields (∼1.5 V/μm), high current operation (∼100 mA/cm(2)) and very high local field amplification factors (up to ∼7300) were demonstrated, and these parameters are most beneficial for use in vacuum microelectronic applications.

Advanced composite materials are characterized by lightweight and unusually high stiffness, strength, modulus, etc. [ 1 , 2 ]. Their application field keeps on expanding as cheaper methods for synthesizing raw materials are found. Composite materials are now found in virtually all facets of applied materials [3] . Unlike a few decades ago when their application was limited to small parts; for example spoilers, failings, bonnets, etc., currently a new generation of airplane fuselage and wings are completely made of high-performance fiber reinforced composites [ 4 – 6 ]. The inherent high specific strength, low density, chemical and corrosion resistance [7] make them ideal for future applications. Typically, composite materials consist of a combination of two or more materials that are mixed with an aim of achieving a specific structural properties [8] . An effective composite should be able to optimize the properties of the individual components as one.

Strong van der Waals forces between individual carbon nanotubes pose a major hurdle for effective use of nanotubes as reinforcement in nanocomposite due to agglomeration. In this paper, the authors show that van der Waals forces in combination with functionalization of carbon nanotubes, can be utilized to design nanocomposites mimicking stiffening behavior normally observed in biological materials such as fibrin gels, health bones, actin filaments in cytoskeletons etc. Carbon nanotube spheres are used as reinforcement in an elastomer matrix and when subjected to dynamic loads exhibit significant selfstiffening. Increased stiffness is also observed in dynamic loading after every relaxation cycle. The authors further show high energy absorption of the nanocomposite in impact tests. Authors study shows that the rational design of macroscale materials from nano-scale constituents can be achieved utilizing simple methodology to produce multifunctional materials with broad applications.Stiffening behavior in presence of dynamic loads is a common phenomenon in majority of biological materials, [1] such as fibrin gels, [2] bones, actin filaments in cytoskeletons [3,4] etc. The stiffening mechanism in natural materials is normally employed as damage prevention measure, when a material is under large deformation. [5] This ability to stiffen with dynamic loads are well demonstrated by healthy bones that adapt to loads regularly. [6] This means, as the loading increases at a certain part of the bone, that specific area of the bone will "remodel" [7][8][9] itself over time to become stronger in order to resist subsequent loads. [6] Designing synthetic materials, mimicking this self-stiffening properties of biological materials can have far reaching implications especially in structures, such as bridges, skyscrapers skeletons structures, airplanes, cars, and ships due to the dynamic loads imposed on them regularly. It is a tall-order to design synthetic materials, which are responsive to dynamic load like their natural counterparts. So far, improvement in various properties have been achieved, [10][11][12] but responsiveness has proved elusive. For instance, metallurgists have perfected a cold working [13] or strain hardening method with an aim of increasing material strength through plastic deformation by dislocation generation and movement within the crystal structure of the material. [14,15] This method though effective for metals, still has major drawbacks, for example, cold working should be done below recrystallization temperature to avoid rearrangement of dislocations at higher temperature, where very little strength can be achieved. Further, as we move toward lighter materials, for example, polymer composites, this method is not applicable. There is an enormous effort by researchers to mimic the efficient design offered by nature. [10][11][12]16] Nanotechnology is allowing researchers and engineers to design very sophisticated materials using bottom-up designs, which were impossible to achieve using conventional method...