Core-corona interface

The fozs-2,2/ 6/,2/terpyridine-ruthenium(II) complexes are assumed to be located at the core/corona interface, as schematically depicted in Fig. 23. 

Small-angle scattering intensity in the high angle (q) region can be analysed to provide information on interface thickness (e.g. the lamellar interface thickness block in copolymer melts or core-corona interface widths in micelles). For a perfectly sharp interface, the scattered intensity in the POrod regime falls as q A (Porod 1951). For an interface of finite width this is modified to... 

Fig. 2 Tentative structures of the bi-layered membrane of PBig5- -PLLysg8 vesicles at different pH b denotes the average distance of chains at the core-corona interface. Reprinted with permission from [22], copyright (2007) American Chemical Society...

Here, the second virial coefficient (excluded-volume parameter), vb = [1 -2x T)]<0, is negative because water is a poor solvent for the hydrophobic block B. The third virial coefficient, Wb, is positive, and x= T- e /d is the relative deviation from the theta temperature. At small deviations from the theta point, r < 1, the surface tension y and the polymer volume fraction (p are related as y/k T = (p. However, at larger deviations from the theta point, (p becomes comparable to unity and the latter relationship breaks down. Because in a typical experimental situation (p = 1, we treat (p and y as two independent parameters. Note that in a general case, surface tension y and width A of the core-corona interface depend on both the polymer-solvent interaction parameter Xbs T) for the core-forming block and the incompatibility Xab between monomers of blocks A and B. That is, y could depend on the concentration of monomers of the coronal block A near the core surface. We, however, neglect this (weak) dependence and assume that the surface tension y is not affected by conformations of the coronal blocks in a micelle. 

For strongly asymmetric copolymers, Na > Nb, the structure of a micelle is controlled by the balance of the coronal free energy, corona, and the excess free energy of the core-corona interface, Finterfaoe-... 

It decreases as a function of the salt concentration. Balancing the free energy, (91), with the excess free energy of the core-corona interface, (24), gives the equilibrium interfacial area per copolymer chain ... 

As expected, the aggregation number increases with increasing salt concentration Oion. The corresponding power law exponent, 6/5, is remarkably larger than in the case of starlike micelles. This is due to stronger repulsive interactions between PE blocks in the quasi-planar corona of a crew-cut micelle as compared to those in a starlike corona. Similarly to the case of a starlike micelle, the thickness of the corona, //corona, in a crew-cut micelle decreases as a function of the salt concentration, ion, although the area x(Oion) per PE chain at the core-corona interface decreases ... 

The scattering amplitude for the core including a graded core-corona interface (Gaussian distribution) can thus for a spherical or cylindrical core be written as ... 

Deviations of the parameter a from the theoretical value may be due to small variations in local structural properties of the activated complex during the expulsion process. Here, factors like screening of solvent/core polymer contacts by the corona block and ill-defined core-corona interfaces might come into play. However, discrepancies could also arise from small uncertainties in the determination of polymer characteristics. However, these discrepancies are obviously system-specific and depend on selective solvent, type of block polymer, temperature, and degree of polymerization and are thus of minor relevance for the general understanding of equdibrium kinetics. From the experimental point of view, a more systematic study... 

In addition to factors affecting the properties of the micelles, the localization of the drug within the micellar assembly is expected to influence the release, with molecules located at the core/corona interface or within the corona diffusing faster than those located in the core. ... 

Here, the term Fcorona includes contributions of conformational entropy of the coronal blocks and the (repulsive) interactions in the coronal domain. The term Finterface is the excess free energy of the core-corona interface it is proportional to the interfacial area s per copolymer molecule ... 

The first three terms are similar to those in Eq. (59). The first is the reduction in interaction energy when the incompatible copolymer blocks avoid contacts with the host by forming the micelle cores. The second term is the interfacial energy, in this case arising primarily from the core-corona interface. The third is the stretching term, which differs for the core and corona blocks but has the same functional form for each one. The final, and new, term is due to the reduction in entropy that occurs when the copolymers are localized to micelles. 

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