Glassy core

This technique does not, however, overcome the formation of frozen micelles due to the formation of glassy cores at a specific nonselective solvent/selective solvent composition. Polydisperse micelles can also be generated during this preparation process if the starting material is characterized by a composition or MW polydispersity. In this respect, micelles will be first formed by the chains containing the larger insoluble block during the addition of the selective solvent. 

Figure 6.5 Illustrations of nanoscale spherical assemblies resulting from block copolymer phase separation in solution are shown, along with the chemical compositions that have been employed to generate each of the nanostructures (a) core crosslinked polymer micelles (b) shell crosslinked polymer micelles (SCKs) with glassy cores (c) SCKs with fluid cores (d) SCKs with crystalline cores (e) nanocages, produced from removal of the core of SCKs (f) SCKs with the crosslinked shell shielded from solution by an additional layer of surface-attached linear polymer chains (g) crosslinked vesicles (h) shaved hollow nanospheres produced from cleavage of the internally and externally attached linear polymer chains from the structure of (g)...

Fig. 3—Glassy core volume decrease of tablets KET-R vs. time , pH 1.2 pH 6.8.

Precirol was successf ully used as a retardant in matrix tablet formulations [8]. The effect of Precirol incorporation into the hydroxypropylmethylcellulose matrix tablets was therefore investigated. Precirol drug ratios of 1 3, 1 2 and 1 1 were used (tablets KET-R A, B, and C). No significant differences in the volume decrease profiles of glassy cores and in ketoprofen release profiles (Fig. 4) in comparison with original core were obtained, even with increased Precirol. 

Fig. 9. Illustration of moving front model for swelling of a glassy polymer gel. Gel assumed to be thin slab. t0 Initially dry glassy state. t, At early and intermediate times after immersion in swelling solution gel contains glassy core and swollen rubbery periphery, with fronts separating the two phases. Core constraints swelling of periphery to occur only normal to front. t2 After fronts meet, swelling constraint vanishes, and swelling permitted in all directions. [Adapted with permission from Ret 24. Copyright CRC Press, Inc. Boca Raton, FL]...

A crosslinked rubber may be synthesized at the surface of the glass beads to produce a core-shell structure (glassy core and rubbery shell). Thermosets modified with these particles showed a strong toughening effect for an optimum thickness of the rubbery shell (Amdouni et al., 1992). 

Case II transport occurs when the sorption is entirely controlled by stress-induced relaxations taking place at a sharp boundary separating an outer swollen shell, essentially at equihbrium penetrant concentration, from an unpenetrated glassy core. Ideally, this sharp boundary moves through the polymer at a constant velocity during case II transport. Super-case II transport occurs when the velocity of the case II sorption boundary is sufficiently slow so that a Fickian tail may develop ahead of the sorption discontinuity [63]. 

The effect of the glassy core in three-layer particles is further demonstrated by the data for the 3LA and 3LE materials. These materials contain particles with essentially identical rubbery-layer outer diameters (284 and 290 nm, respectively), but with glassy-core diameters of 200 and 244 nm, respectively. The values of GIc for these materials are similar when plotted against Vp, but,... 

Finally, comparison of GIc. values for the 3LA materials with those for the equivalent 4L materials demonstrates that, contrary to patent claims (5), the introduction of a 100 nm diameter rubbery core into the glassy core of the 3LA particle has no significant effect on fracture resistance. 

This fixed the moving boundary as varies from 0 to 1. This transform is valid till the glassy core disappears. Once the glassy core disappears, symmetry conditions for both the solvent concentration and the stress prevail at x = 0. The new Landau transform that fixes the rubbery solvent interface is... 

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