Dissipative structures micro

Nmabu, T., Yamuachi, Y., Kushiro, T., Sakurai, S. Micro-convection, dissipative structure and pattern formation in polymer blend solutions under temperature gradients. Faraday Discuss. 128, 285-98 (2005)... 

If the concentration is low, rather than thin films dissipative structures (e.g., convection patterns, fingering instabilities) are produced [87]. Such work was subsequently used to topographically control neurite extension on stripe-patterned polymer films [150], fabrication of periodic micro-structured honeycomb films having multiple periodicities, and polymer nanoparticles [151]. Large-scale ordering was observed. This was defined by the periodic thickness modulation of a block-copolymer film due to the self-organization of the receding contact line [152]. 

These results, combining the widely known instability (and dissipative structure ) phenomenon of melt fracture with the new nonequilibrium description of multiphase polymer systems, will hopefully stimulate more experimental and theoretical work devoted to these (frozen) dissipative structures. It still remains an open question which property of the melt may be responsible for its suddenly occurring capability to disperse fillers (pigments, carbon black, etc.) or other incompatible polymers above melt fracture conditions. We can only speculate that, in particular, the creation of micro voids (inner surfaces) and a sudden increase in gas solubilization capability at and above melt fracture allow the polymer melt to wet the surface of the material that is to be dispersed. This means that a polymer melt might have completely different (supercritical) properties above melt fracture than we usually observe. 

At the formation of the structure of crosslinked polymers one can observe the formation of dissipative structures (DS) of two levels - micro- and macro-DS. Micro-DS are local order domains (clusters) and their formation is due to the high viscosity of the reactive medium in the gelation period. As it is known [47], this results in turbulence of viscous media and subsequent formation of ordered regions. 

When the stress that can be bom at the interface between two glassy polymers increases to the point that a craze can form then the toughness increases considerably as energy is now dissipated in forming and extending the craze structure. The most used model that describes the micro-mechanics of crazing failure was proposed by Brown [8] in a fairly simple and approximate form. This model has since been improved and extended by a number of authors. As the original form of the model is simple and physically intuitive it will be described first and then the improvements will be discussed. 

Computational fluid dynamics enables us to investigate the time-dependent behavior of what happens inside a reactor with spatial resolution from the micro to the reactor scale. That is to say, CFD in itself allows a multi-scale description of chemical reactors. To this end, for single-phase flow, the space resolution of the CFD model should go down to the scales of the smallest dissipative eddies (Kolmogorov scales) (Pope, 2000), which is inversely proportional to Re-3/4 and of the orders of magnitude of microns to millimeters for typical reactors. On such scales, the Navier-Stokes (NS) equations can be expected to apply directly to predict the hydrodynamics of well-defined system, resolving all the meso-scale structures. That is the merit of the so-called DNS. 

As an example we consider the flow of a fluid/adsorbate mixture through the big pores of a skeleton, thought like an elastic solid with an ellipsoidal microstructure, and propose suitable constitutive equations to study the coupling of adsorption and diffusion under isothermal conditions in particular, we insert the concentration of adsorbate and its gradient in the usual variables, other than microstructural ones. Finally, the expression of the dissipation shows clearly its dependence on the adsorption and the diffusion, other than on the micro-structural interactions. The model was already applied by G. and Palumbo [7] to describe the transport of pollutants with rainwater in soil. 

There are many applications where the physical properties of a textile substrate are combined with the electrical and shielding properties of polypyrrole. Thus polypyrrole-coated fabrics show excellent dissipation properties. In this way industrial uniforms where explosion-proof conditions or shielding fi om micro-waves are necessary can be fabricated, as well as the use of polypyrrole-coated filters where static charges could cause the explosion of flammable solvents. Other important applications are related to military equipment, as radar-absorbing sheets. The microwave response of those fabrics seems to be ideal for camouflage nets that avoid visual, near-infrared and radar detection. Textile fabrics have also applications in fiber-reinforced composite structures of different resins. 

Polymer A and Polymer E exhibit an initial elastic stretch, followed by a region of viscoelastic behaviour. After approximately 60 s, a Newtonian response is seen. No elastic recovery is evident once the stress is removed as the stored elastic response has been dissipated during the timescale of the experiment. In contrast, Polymer D shows less displacement when the stress is first applied, indicative of a more rigid structure. The very shallow gradient of the slope beyond 60 s reflects the very high apparent viscosity imder these conditions. Once the stress is removed, a visible elastic recovery is evident from the network within the polymeric micro-particles. 

For gases, 5c 1, for hquids. Sc 1. This implies that in turbulent flow of liquids, the species concentration field contains smaller scale structures than the velocity field. Similar to the decay time of the turbulent eddies in the velocity field, Tu, (12.2-1), the decay time of the eddies in the species concentration field, the previously introduced micro-mixing time, xy, can be modeled in terms of the correlation of the species mass fraction fluctuations, the so-called scalar (co-) variance, (K F), and its dissipation rate, the so-called scalar dissipation rate, sy. 

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