Particle-wall interactions, evaluation

Particle-wall and particle-particle interactions in the colloid can be evaluated by several techniques. For charged particles, the distribution of electric fields which are required to remove them from the wall can be readily obtained by optical methods(ll, 12). The removal fields together with particle charge, then yield the particle-wall forces which include electrostatic, van der Waals and steric forces. The most direct way of following particle-particle forces is to study the volume changes of the colloid caused by applied pressure (20) in an arrangement where liquid is allowed to escape freely. 

Fluorescent dyes as markers can also be used to follow particle-cell interactions, via LSM and FACS measurements. Hence, polyure thane/urea capsules were created in inverse miniemulsion that could encapsulate a fluorescent dye with 90% efficiency [129]. In this case, carboxymethylation was carried out on the particle surface, followed by the physical adsorption of poly(2-aminoethylmethacrylate) or polyethylene imine polycations. As expected, the rate of uptake of capsules modified by the polycation was higher than for non-modified capsules. Rosenbauer et al. applied the same synthetic procedure, but in the presence of a surfactant that crosslinked the shell [130]. The commercially available surfactant containing several amine groups reacted with the diioscyanate monomer subsequently, the capsule shell wall was found to be less permeable than capsules synthesized with a non-crosslinkable surfactant. Baier el al. used the above-described synthesis to perform a polymerase chain reaction (PCR) in crosslinked starch nanocapsules [131]. The permeability of the shell was also evaluated using fluorescence spectroscopy. The combination of a cleavable polyurethane [132] with the interfacial polyaddition described above [126] afforded polymer shells that could be opened by ultraviolet (UV) irradiation, or by modifying the temperature or pH [133], In order to determine the release of encapsulated sulforhodamine dye, polyurethanes with... 

Several workers have inferred the existence of a radial velocity profile in a packed bed of low tube-to-particle diameter ratio from measurements of the fluid velocity at the bed exit [30]. However, their results are in considerable disagreement. A semi-theoretical study, using a modified Brinkmann model [31], indicates the existence of a steep maximum in the velocity next to the wall, but this remains unsubstantiated. Non-intrusive measurements of gas velocity within the packed bed are needed before a proper evaluation of the interactions of radial velocity, radial heat transfer, conversion and reaction selectivity are forthcoming. 

Application of CFD to describe air bubbling is an area of intense activity, with the effects of air flowrate, intensity, bubble shape, diameter and frequency of particular interest. The major purpose of modelling the behaviour of bubbles is to evaluate the shear stress on the membrane wall. However, the interactions between the particles and bubbles are stiU not clear. For example, how are the floe shape and size and EPS formation affected by air bubbling Both floes and extracellular polymeric substances (or extracellular polysaccharides, EPS) contribute to formation of the cake layer and may block the membrane pores, with the extent of fouling potentially affected by the size of any particulates present. Models for cake layer build up and the removal by shear are still not well developed. Moreover, it is unclear how accurately the viscosity of the sludge should be modelled. The viscosity of the sludge could affect the extent of shear experienced by the floes but the inclusion of viscosity models... 

Recently, the usage of nanoscale fillers as reinforcements for various polymer systems has been rampant [1-4]. One of the most frequently used nano-reinforcements is silica, as it is relatively cheap and easily available. In this study, PMMA grafted micro- and nano-scale silica particles were incorporated into poly (methyl methacrylate) (PMMA), which was molded using thin-wall micromolding technology. The dispersion of these fillers was evaluated and later correlated to the filler-matrix interaction and mechanical properties of the moldings. 

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