Coated droplets

Carbon monoxide and dioxide oxidize zinc vapor below 1100—1300°C although only the carbon dioxide reaction is significant. Rapid condensation of the zinc vapor avoids the formation of ziac-oxide-coated droplets, so-called blue powder. 

Kaiser, T. Roll, G. Schweiger, G., Investigation of coated droplets in an optical trap Raman scattering, elastic light scattering, and evaporation characteristics, Appl. Opt. 1996, 35,... 

The outer and core radii were determined from optical resonance measurements using Mie theory solutions (Aden and Kerker, 1951 Bohren and Huffman, 1983) for concentric spheres to interpret the resonance spectra. Figure 36 presents some of the data of Ray et al. for a pure component glycerol droplet and for a coated droplet having an initial coating thickness given by yo = 0-321. Here y is a reduced thickness defined by y = (a - aj/a. 

Figure 3.5 Demonstration of correlation between the stickiness of protein-coated droplet pair encounters in shear flow (left ordinate axis) and viscoelasticity of concentrated emulsions (right ordinate axis) with the strength of protein-protein attraction as indicated by the second virial coefficient A2 determined from static light scattering , percentage capture efficiency (0%) A, complex shear modulus (G ) for emulsions stabilized by asl-casein or (3-casein (pH = 5.5, ionic strength in the range 0.01-0.2 M).

Another way to interpret the above observations would be in terms of the general principle that effective steric stabilization of polymer-coated droplets requires that the continuous phase be a good quality solvent for the polymeric stabilizer. Under poor quality solvent conditions (asi-casein at high ionic strength), the required entropic stabilizing repulsion of the adsorbed protein layer is converted into a destabilizing polymer-mediated attraction (Dickinson and Stainsby, 1982 Dickinson, 2006). 

Experiments on interactions of polysaccharides with casein micelles show similar trends to those with casein-coated droplets. For example, Maroziene and de Kruif (2000) demonstrated the pH-reversible adsorption of pectin molecules onto casein micelles at pH = 5.3, with bridging flocculation of casein micelles observed at low polysaccharide concentrations. In turn, Tromp et al. (2004) have found that complexes of casein micelles with adsorbed high-methoxy pectin (DE = 72.2%) form a self-supporting network which can provide colloidal stability in acidified milk drinks. It was inferred that non-adsorbed pectin in the serum was linked to this network owing to the absence of mobility of all the pectin in the micellar casein dispersion. Hence it seems that the presence of non-adsorbed pectin is not needed to maintain stability of an acid milk drink system. It was stated by Tromp et al. (2004) that the adsorption of pectin was irreversible in practical terms, i.e., the polysaccharide did not desorb under the influence of thermal motion. 

A critical parameter for obtaining films with desirable properties is the creation of coating droplets, a process often referred to as atomization, that is, when a bulk liquid is dispersed in air to form a spray or a mist [61]. Atomization is done by letting pressurized air and bulk solution pass simultaneously through a nozzle (spray... 

The rotor is very flexible regarding batch size. Minimum batch size may be as low as 1/8 of working capacity. However, when applying films, the batch size should be selected such that the nozzle is immersed below the surface of the bed. This minimizes the potential that the high velocity atomization air will not blow some coating droplets through the bed where they may be spray dried and collected in the filter. 

Orange Peel Film surface has a rough finish resembling orange peel. Film coat droplets are too dry or too viscous to spread on tablet surface. Reduce solids content of coating suspension. Reduce drying temperature. Reduce viscosity of polymer. 

The atomized coating droplets must be significantly smaller than the particle to be coated in order to obtain a uniform and complete coating and avoiding agglomeration (Gouin, 2004). 

Coated droplets Colloidosomes Dry waters Pearl drops... 

Airless electrostatic spray coating. The airless electrostatic spray coating method (70 to 80% TE) uses airless spray guns with the addition of a dc power source that electrostatically charges the coating droplets. 

The final class of behaviour in oil - - water + surfactant systems is the formation of bicontinuous liquids. In an oil-swollen micelle or o/w microemulsion, the oil is clearly inside the surfactant aggregate, and when it is swollen beyond its limit, bulk excess oil will be observed. Likewise in w/o emulsions, the system can lake up only so much water within the surfactant-coated droplets. But there is also a third class of microemulsions in which neither oil nor water can be regarded as inside or outside of the aggregates. These are referred to as bicontinuous (or more properly tricontinuous) liquids, in which the surfactant forms a flexible monolayer within the liquid separating oil from water microdomains, but without enclosing either. Thus both liquids, as well as the surfactant film, are continuous throughout the liquid, as depicted schematically in Figure 7. 

Significant mechanical agitation of oil and water along with a small amount of an appropriate surfactant often creates an emulsion, i.e. a two-phase dispersion, where surfactant-coated droplets of one phase are dispersed into a continuous phase (see Chapter 8... 

Rieka, J., Borkovec, M. and Hofmeier, U., Coated droplet model of microemulsions optical matching and polydis-persity, J. Chem. Phys., 94, 8503-8509 (1991). 

Rieka J, Borkovec M and Hofmeier U. 1991. Coated droplet model of microemulsions - optical matching and polydispersity. Journal of Chemical Physics 8503-8509. 

For bridging flocculation to occur, several conditions must be met. The most obvious is that the droplet surfaces must be subject to polymer adsorption. In emulsions, the presence of surfactants at the interface, which are necessary for coalescence stability, means that only polymers with sufficient surface affinity to displace the surfactant from the siuface, or a specific affinity for the surfactant itself, may adsorb. A second condition places a lower limit on the size of the polymers in a given system. Clearly the partially coated droplets must encounter one another, coming close enough for a polymer molecule to span the gsq> between the droplets. This means that the polymer molecules must be able to extend past the primary maximum in the total interaction potential. The absolute limit on polymer size will be defined by the position of the primary maximum and the radius of gyration of the polymer molecules. However, in practice, when polymer molecules become adsorbed to drop surfaces the conformation of the polymer molecule frequently alters to allow multiple attachments to the drop surface, which may reduce the distance the polymer extends into solution. 

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