Spherical capsules

These two seemingly dissimilar applications have a common basis—both are examples of the pressure-sensitive release of a chemical. How are these products designed Tiny spherical capsules (microcapsules or microspheres) with a glass or polymer shell are filled with a liquid core and glued onto paper. For a scratch-and-sniff ad, the core of the microcapsules contains a liquid with the desired scent for carbonless paper, a liquid ink or dye is encapsulated within the... 

A limited number of polyanion-polycation systems were tested using a droplet/falling annulus method (Fig. 4). This technique, which has been described elsewhere [64] reduces the net impact velocity between the droplet with the oppositely charged counterion fluid. A stream of droplets was directed into a collapsing annular liquid sheet. By matching the velocities of the droplet and sheets, the impact conditions can be moderated. It has been shown to produce monodisperse spherical capsules, though it requires several days of calibration for each new system and is obviously not practical for a massive screening such as was carried out herein. 

Liposome A spherical capsule consisting of a liquid core surrounded by a lipid bilayer. 

In aqueous media, they assemble into spherical capsules capable of encapsulating Nile Red with remarkably low CMC values (2 x 10 M for G1 and 3 x 10 M for G2). Similarly, the size of the aggregate derived from a related dendron-rod-dendron copolymer, composed of a phenylene vinylene rod capped on each end by amphiphilic polyether dendrons, could be tuned in the melt state by modifying the generation level of the dendron (Fig. 11.28 Lee et al. 2002). 

A tennis-ball-shaped molecular aggregate can be constructed by the self-assembly of curved molecule I. Tetrameric assembly of II generates a pseudo-spherical capsule. Dimeric assembly of III can be induced by the encapsulation of smaller molecules of appropriate size and shape at the center of a spherical complex. 

Compound 50c was obtained in ca. 25% yield as a precipitate from the acid-catalyzed condensation of pyrogallol and isovaleraldehyde. No evidence of any hexamer was found in the solid material. To convert this material into the hexamer (50c)6, the original precipitate can be dissolved in Et20, acetone, or methanol, with a few drops of nitrobenzene or o-dinitrobenzene, followed by crystallization upon slow evaporation. The hexamer may also be obtained by thermal treatment of the initial precipitate or the initial filtrate. The product in the initial filtrate may be converted into hexamer by extraction in Et20, followed by evaporation to dryness with subsequent dissolution in methanol. The methanol solution is then heated to 120-150 °C for at least 12 h. Methanol may be removed under vacuum to yield a red-brown solid. Colorless hexameric spherical capsules are obtained from this solid utilizing the crystallization procedure described for the initial precipitate. 

In a spray-drying method of encapsulation, Zhao and Whistler (1994) suspended starch to a concentration of 30% in water containing 0.1-1.0% gelatin or any of a number of polysaccharide bonding agents the suspension was forced through an orifice (2 mm diameter) under 80-100 psig at an inlet temperature of 120°C and outlet temperature of 76°C. Porous 10-40-nm-diameter spherical capsules were obtained that were then immersed in peppermint oil. After diffusion of the peppermint oil into the capsules, the spheres were rinsed free of oil and coated in a fluidized bed with a 3%... 

Besides these covalently constructed cage-type receptors a number of self-assembled capsules with hydrogen bond donors protruding to the inside have also been described. An early example was reported by Atwood et al. This system makes use of the well known properties of resorcin[4]arene 30a and pyrogallol[4]arene 30b to form hexameric spherical capsules in the solid state and, in the case of 30b, also in solution. 

Figure 12 (a) The spherical capsule consisting of six pyrogallol[4]arene molecules shown in... 

Plate 22 (Figure 3.12). (a) he spherical capsule consisting of six pyrogallol[4]arene molecules shown in the capped-stick metaphor, and (b) with the carbon and hydrogen atoms removed. Hydrogen bonds are shown as thin, solid red lines. Parts (c) and (d) show the remarkable correspondence of the hydrogen bonded pattern with the Archimediean solid, the small rhombicuboctahedron. 

Figure 3.6 A pseudo-spherical capsule composed of bridged glycoluril subunits linked by hydrogen bonds ...

A theoretical approach to calculate the burst time from an osmotically active spherical capsule, which depended on the initial radius, wall thickness, osmotic pressure of the contents, and the material of the capsule, has been presented. This approach assumed that the spherical core increases in size upon osmotic water influx, leading to an elongation of the membrane until a certain yield stress is reached to rupture it. The rate of volume increase was described by the following equation ... 

A. Muller, S.K. Das, E. Krickemeyer, P. Kogerler, H. Bogge, and M. Schmidtmann, Cross-linking nanostructured spherical capsules as building units by crystal engineering related chemistry, SolidState Sci. 2 847 (2000). 

Tan, F.L. Hosseinizadeh, S.F. Khodadadi, J.M. Fan, L. Experimental and computational study of constrained melting of phase change materials (PCM) inside a spherical capsule. Int J Heat Mass Tran 52 (2009) 3464-3472. 

Both synthetic (biodegradable not) and natural polymers have been proposed and te.sted as drug delivery systems (104,105). It was Speiscr( 104.106) who first prepared spherical capsules made of a polymeric material capable of being loaded with active drugs by entrapment or adsorption. The method was based on the so-called micellar polymerization of. such monomers as acrylamide or methyl methacrylate. Since those first contributions, the number of monomers potentially useful in the field, as well as the polymerization routes employed have grown almost exponentially, and so have the fields of application in pharmaceutical dosage. 

Description Herbaceous annual or biennial with multiple branches. Stems quadrangular, glabrous, 10-25 cm long. Leaves opposite, sessile, ovate to elongate-ovate, with black dots on abaxial surface. Rowers brick-red, individual, with long pedicels. Fruit a spherical capsule, opening by a small cover. Seeds small, oval, 3-sided, black, many in each capsule. 

Egg-shaped or spherical capsules can be formed by the assembly of two halves or hemispheres. Like then-covalent carcerand and hemicarcerand counterparts, self-assembled capsules are of interest for drug delivery and as containers for stabilizing reactive intermediates and for inducing selectivity in reactions. Capsules have been... 

Smart Polymers and their Applications Spherical capsules containing healing agents... 

Fibres as heahng agent carriers have been used almost since the first successful attempts to demonstrate the self-healing concept in engineering materials (Dry et al, 1993). As for spherical capsules, the healing mechanism is based on a liquid confined in a container (fibre in this case) which, upon rupture, leads to release of the agent and subsequent reaction. The main... 

In 2010, Blaiszik et al (2010b) combined the use of fibres with spherical capsules to restore the adhesion between fibre and matrix. In their approach they coated E-glass fibres with Grubbs catalyst and with 1.5 pm diameter capsules containing dicyclopentadiene. This approach did not affect the intrinsic mechanical properties of the fibres and the composite while the system showed significant, although not optimal, interfadal shear strength recovery. 

Effect of radius of curvature, R, and central angle, a, of the bend section of pipe on threshold velocity of capsules, V/r, capsule liquid velocity ratio, Vc v , and hydraulic gradient U, is important to satisfy transport capacity and safe operation of capsule pipelining. Based on experimental investigation done with heavy cylindrical and spherical capsules [9-13] it was found that the threshold velocity is practically independent on central angle of the bend section (see Fig. 1), if the pipe curvature is adequate, as it is given by relationship [4,6]... 

Increment of pressure gradient for flat-ended capsules of volumetric concentration Cv = 40 % is about 40%, for bullet-shaped ones even 50 %, while for wheeled or spherical capsules is only 20 %, what corresponds to the increment for flow of liquid alone [13]. 

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