Viscous encapsulation

The extent of the interface distortion will depend on the length of the flow channel. If the channel is long enough the high-viscosity fluid will be completely encapsulated as shown in Fig. 9.42. If the channel is short the interface distortion will show an intermediate configuration as shown in time ti or t2 in Fig. 9.42. The process of viscous encapsulation was studied by Gifford, as discussed in Section 12.4.2 see Fig. 12.18. 

It appears that there are several mechanisms for interface distortion. One is distortion caused by viscosity differences (viscous encapsulation), another is caused by normal stress differences in the fluid (elastic encapsulation), and a third is caused by normal velocity differences within the fluid (geometrical encapsulation). Obviously, the distortion will increase when viscosity differences are large and when normal stress differences play a significant role. 

The smallest viscosity ratio simulated, (pa/Pb = 0-1). demonstrates that the smaller viscosity material is starting to flow around the higher viscosity material producing a nonuniform layer thickness-a phenomenon called viscous encapsulation. The effect of the flow rate ratio (Qa/Qb) on the interface between the two polymers is... 

The component with the lower viscosity tends to encapsulate the more viscous (or more elastic) component (207) during mixing, because this reduces the rate of energy dissipation. Thus the viscosities may be used to offset the effect of the proportions of the components to control which phase is continuous (2,209). Frequently, there is an intermediate situation where a cocontinuous or interpenetrating network of phases can be generated by careflil control of composition, microrheology, and processing conditions. Rubbery thermoplastic blends have been produced by this route (212). 

To reduce the amount of downdrag force on the waste pile, standpipes can be coated with viscous or low friction coating. Standpipes can be encapsulated with multiple layers of HDPE. This material has a very low coefficient of friction that helps reduce the amount of downdrag force on the waste piles. 

The low IFT value found immediately after formation of the G/P complex coacervate phase/lemon oil 1 interfaces at 45°C also favors preferential wetting of lemon oil 1 by the G/P complex coacervate phase. The G/P complex coacervate phase is too viscous for an IFT measurement at 40°C, and it has gelled at 35°C, so wetting of lemon oil 1 by a G/P complex coacervate phase should not be a problem during a G/P complex coacervation encapsulation process. 

Even more recent has been the introduction of cncapsiilaiion/exirusion. which also permits conversion of Havorants. such as essential oils, into solid form. Spray drying is nut required. In the encapsulation process, the flavor substance is "enrobed." A viscous carbohydrate, with less than ]O f water, is created by heating, after which an emulsifier and acid flavoring ingredients are added. The ingredients are reacted under pressure in a cool alcohol bath, and then the product is extruded to fornt filaments, Thus, the final easy-to-handle product contains the flavor within a small capsule. 

Similar result brings comparison of power consumption reduction for transport of encapsulated viscous liquid (Russian oil) conveyed by water with conventional pipeline transport of the oil. Transport of viscous oil and oil products by means of capsule pipelining may again provide power consumption reduction from 50% to 70%, the reduction increases with operational velocity. Since for low temperature the oil viscosity significantly increases hydraulic capsule pipeline transport of highly viscous oil and oil products for long distances in arctic conditions can be economically attractive. Capsule pipeline transport could be recommended as suitable transport especially for longer distances when power consumption becomes the most important for operational cost. 

Particles as small as 50-100 mesh can be encapsulated. It is essential to keep the particles in continuous motion—e.g., by simple rotation of the bottle to maintain a tumbling bank—to prevent agglomeration and sticking. Since no solvents are involved and no liquid viscous stage is encountered during the polymerization, coherent, uniform coatings are deposited around each particle. 

Fig. 10 Schematic representation of surfactant in multilamellar droplet phase with entrapped metal ions (M ) in the aqueous phase (W) layers, which are separated by surfactant bilayers. The number of layers (hence the size of the surfactant droplet) is dependent on temperature and concentration. When the surfactant head group is positively charged thus encapsulating oppositely charged metal ions, under an electric field, surfactant lamellar droplets migrate to the anode and form a highly stable viscous gel in which the positively charged metal ions are concentrated at the anode only separated by the surfactant bilayer. (From...

For much less viscous 30,000 MW PGLA solutions, a skin did not form in the vapor phase. The particles did not form until the large droplets dispersed on contact with the liquid CO2 phase, which was agitated to improve mixing. The resulting spherical particles ranged from 3 to 25 pm in diameter. It is shown later that these particles may be used to encapsulate proteins. 

Polymer formulations have been suggested to enable application of IJ to foliage in a protected state, for example, nematode encapsulation in sodium alginate immediately before application has been used, so that, at the target surface, the nematode-in-gel formulation is still viscous (Navon et al., 1998). However, the separate application may prove difficult technically, due to rheological problems. 

Polymers of this nature can be polymerized either in solution or in bulk in the latter case they are normally reacted at high temperatures, e.g., 100-150 C. Since our goal was a casting resin, the formulations were reacted in bulk and at lower temperatures to protect heat sensitive electronic components furthermore, low reaction temperatures minimize side reactions that can lead to crosslinking and polymer insolubility. In this process the polyols and diisocyanates were mixed and allowed to react for about 25 minutes at 71 C to form the prepolymer formation while longer times resulted in material too viscous to cast or deaerate. After the indicated time, 1,4-butanediol was added followed by deaeration and subsequent encapsulation of a preheated (71 C) electronic device. A second deaeration of the encapsulated part is usually necessary. Pot life for such a system is about 15 minutes. Final reaction or "cure" was 24 hours at 71 C. 

Microcapsules containing polymer and pigment were prepared in [299] by dispersing a viscous suspension of pigment and oil-soluble shell monomer forming o/w emulsions. Subsequently, a water-soluble shell monomer was added to the emulsion droplets, encapsulating them via interfacial polycondensation. These microcapsules were then heated for free radical polymerisation of the core monomers. It has been shown that polyvinyl alcohol (PVOH) used as stabiliser reacts with the oil-soluble shell monomers. The decrease of PVOH concentration as result of this interaction leads to coalescence of the particles and to the increase of their equilibrium particle size, however, methods are proposed to prevent the depletion of PVOH. 

Elvax 150 softens to a viscous melt above 70°C, and therefore Is not suitable for temperature service above 70°C when employed In a fabricated module. A cure system was developed for Elvax 150 that results In a temperature-stable elastomer ( ). Elvax 150 was also compounded with an antioxidant and UV stabilizers, which Improved Its weather stability and did not affect Its transparency. The formulation of the encapsulation grade ethylene vinyl acetate Is given In Table I. These Ingredients are compounded Into Elvax... 

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