Encapsulated structures

Microfluidic devices can be used both in NP fabrication and for core-shell and matrix encapsulation structures. 

There exist in polymer blends two or three major types of phase morphologies, depending on whether the encapsulated structures (composite droplets) are considered as a class apart. The most common is the droplet-in-matrix (as, for example, Figure 1.3), the (droplet-in-droplet)-in-matrix (as, for example. Figure 1.4), and the cocontinuous phase morphology where both phases are mutually interconnected throughout the whole volume of the blend (as, for example. Figures 1.5 and 1.6). 

Since the discovery of crown ethers by Pedersen there have been many attempts to design and synthesize hosts whose ion affinities and selectivities surpass those of the original cyclic polyethers. Particularly important examples are the cryptands and spherands. These polycyclic receptors form stronger complexes and are generally more selective than crown ethers, however their complexes equilibrate more slowly as a consequence of their more rigid, encapsulating structures. This report is focused on the development of a new class of macrocyclic hosts, the torands, whose rigid toroidal structures should permit rapid equilibration of complexes. 

Present-day life forms are cellular with phospholipid bilayer membranes forming the primary barrier that separates the interior of the cell from the external environment. It has been proposed that similar encapsulating structures, based on, for example, fatty acids, could have self assembled in the prebiological environment, thus providing an enclosed reaction system. It should be noted that in presently evolved biological systems, membranes can contain up to 15% fatty acid content, mixed with phospholipid. 

Overcoated or encapsulated structures have also been investigated, as shown in Fig. 10.4, but only a few materials can be utilised without the metal film suffering a significant loss in marking sensitivity. 

M5 and M6E are typically encapsulated structures and similarly to M4E species are accessible only when E is a first row element. Larger main group elements are not appropriate for these cavities. Selected examples of clusters with stoichiometries M4E, M5E, and M6E are shown in Table 3.2. The most important family of clusters with interstitial or encapsulated atoms are by far the carbides. 

Different morphologies of biopolymer-based encapsulation structures obtained through electrospinning, (a) Zein structures (b) PVOH fibers (c) pullulan structures (d) chitosan capsules. 

Zumbrunnen DA, Ellison MS, Gomillion BL. Composites with encapsulated structures and related method. US Patent 6,902,805 B2 (Assigned to Clemson University) June 7, 2005. 

The examples provided here certainly show how the field of self-assembled nanocapsules is becoming a promising tool for the development of efficient and highly selective catalysts, thanks to the high versatility in terms of size, shape, and interactions of the cavities. In particular, the confinement imposed by the encapsulating structure provides an attractive tool for inducing the formation of less-favored regioisomers or alteration of the bulk physicochemical properties. 

For illustrative purposes, the rheology results shown and discussed in the rest of this paper will be confined to combinations of Resins A and B using the encapsulated structure shown in Figure 2. 

The next set of experiments consisted of extruding two of the polyethylene resins (A and B) in coextraded encapsulated structures with 10% and 20% skin layers in which the skin layer was less viscous than the eore layer. These experiments produced structures with 10% and 20% skin layers of Resin A on 90% and 80% eores of Resin B. The results of these experiments are shown in Figure 7 and are conpared to the results for the individual resins. 

The final set of experiments consisted of measnring the viscosity of encapsulated structures of Resins A and B in which the skin layer thicknesses are varied from 0 to 50% of the total structure. These experiments were ran at a constant shear rate of approximately 40 1/s. The results of these experiments are shown in Figures 9 and 10. 

Figure 9 shows the viscosity of encapsulated structures with a skin layer of Resin A on a core of Resin B as the skin layer thickness is varied from 0 to 50% of the structure. Since Resin A is less viscous than Resin B, a decrease in the structure viscosity would be expected as a layer of Resin A is added to the structure. Figure 9 shows that there is a significant drop in the viscosity of the structure even with just a 5% skin layer of Resin A added to the structure. 

Figure 3. Coextraded encapsulated structures with different skin layer thicknesses.

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