Composite particle geometry

The most important stmctural variables are again polymer composition, density, and ceU size and shape. Stmctural foams have relatively high densities (typically >300 kg/m ) and ceU stmctures similar to those in Figure 2d which are primarily comprised of holes in contrast to a pentagonal dodecahedron type of ceU stmcture in low density plastic foams. Since stmctural foams are generally not uniform in ceU stmcture, they exhibit considerable variation in properties with particle geometry (103). 

Sorption Kinetics. The adsorption and desorption data were analyzed in terms of a model based on the following main assumptions. Micropore diffusion within the sieve crystals is the rate-controlling process. Diffusion may be described by Fick s law for spherical particle geometry with a constant micropore diffusivity. The helium present in the system is inert and plays no direct role in the sorption or diffusion process. Sorption occurs under isothermal conditions. Sorption equilibrium is maintained at the crystal surface, which is subjected to a step change in gas composition. These assumptions lead to the following relation for the amount of ethane adsorbed or desorbed by a single particle as a function of time (Crank, 4). 

Fig. 10 Droplet microfluidics for microparticle synthesis, (a) Janus particle synthesis by coflowing two monomer streams. Reproduced with permission from [82]. (b) Channel geometry facilitated aspherical particles synthesis. Reproduced with permission from [111], (c) Multiple emulsion templated composite particles synthesis. Reproduced with permission from [112]...

If we characterise composites by particle geometry, we can distinguish fibres and particles (in the narrow sense). In fibres, one dimension is larger than the others by at least one order of magnitude, thus they are shaped like long and slender cylinders. In particles, the extension is approximately the same in aU directions. Other structures are also possible the phases may, for example, also be arranged in a sandwich structure or laminate with alternating layers of different materials. 

The ideal resin distribution for a particleboard manufacturer is usually defined by the maximum board properties obtainable when using a given minimal amount of adhesive. The cost of a continuous film of adhesive becomes prohibitive as wood particle size decreases in a composite because of the enormous wood surface area involved. How to obtain and measure the ideal resin distribution is subject to debate. Wood particle geometry, amount of adhesive applied, adhesive application method, spray... 

Figure 13.4 Evidence for the highly tunable nature of the plasmon resonance of gold nanostructures arising from variations in particle geometry and composition.

Fig. 3.62. Geometry of a composite particle consisting of three identical cylinders...

Mass-Transfer Coefficient Denoted by /c, K, and so on, the mass-transfer coefficient is the ratio of the flux to a concentration (or composition) difference. These coefficients generally represent rates of transfer that are much greater than those that occur by diffusion alone, as a result of convection or turbulence at the interface where mass transfer occurs. There exist several principles that relate that coefficient to the diffusivity and other fluid properties and to the intensity of motion and geometry. Examples that are outlined later are the film theoiy, the surface renewal theoiy, and the penetration the-oiy, all of which pertain to ideahzed cases. For many situations of practical interest like investigating the flow inside tubes and over flat surfaces as well as measuring external flowthrough banks of tubes, in fixed beds of particles, and the like, correlations have been developed that follow the same forms as the above theories. Examples of these are provided in the subsequent section on mass-transfer coefficient correlations. 

Chemical composition (including moisture content) Physical composition (i.e., geometry, form, particle size) Thermal mechanical history... 

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