Entrapment, free-energy

Crystallization in miscible blends can occur with rejection of the noncrystallizing component, so that its concentration in the amorphous phase increases. Alternatively, if it can be accommodated in the unit cell, it may be entrapped, with consequent alteration in the mean unit cell volume (Tomlin and Roland, 1993). In NR, there is also a shift to formation from a-lamellae to the )3-lamellar form (Zemel and Roland, 1992b) (Figure 3.25). These crystal structures have the same unit cell, but the latter has a greater fold-surface free energy. Thus, the noncrystallizing blend component is more readily accommodated into the fold plane at the crystal surface. 

In the low salt limit, atCp > the coronal contribution to the free energy is dominated by the translational entropy of counterions entrapped inside the corona, int = k TabNAi riCp - 1). In this case, all results of the blob model are recovered both for osmotic starlike and crew-cut spherical micelles (59), (61), and (62). 

Thus, to decrease the free energy of MIX contact between water and hydrophobic silica should be minimal. A high viscosity of the MIX system and absence of bulk water prevent floating of MS particles that can occur at small amounts of both oxides in a diluted suspension. Therefore, primary particles of A-300 and their aggregates form dense shells (micelles) around MS particles with entrapped air that create a barrier preventing contact of water with MS and the formation of separated MS phase. The LT H NMR and NMR cryoporometry methods give useful structural information on the hydrophilic/hydrophobic silica-water mixtures and can be used to characterize the properties of dry water materials. 

Another possibility, perhaps more appropriate in the case of a continuous phase-separated network, is that the retractive force of the gel arises from a minimization of interfacial energy. For example, if the gel structure is imagined to be cellular, consisting of approximately spherical holes in the polymer-rich phase entrapping the dilute phase, then small deformations at constant volume (illustrated in two dimensions in Fig. 8) would result in an increase in interfacial area and, thus, an increase in free energy. The retractive force in such a... 

Theoretical analyses (75-77) of the matrix-induced changes in the optical spectra of isolated, noble-metal atoms have also been made. The spectra were studied in Ar, Kr, and Xe, and showed a pronounced, reversible-energy shift of the peaks with temperature. The authors discussed the matrix influence in terms of level shift-differences, as well as spin-orbit coupling and crystal-field effects. They concluded that an increase in the matrix temperature enhances the electronic perturbation of the entrapped atom, in contrast to earlier prejudices that the temperature dilation of the surrounding cage moves the properties of the atomic guest towards those of the free atom. 

Fig. 40. Optical spectra of matrix-entrapped (A) Cu(CjH,),jj in Ar, (B) Ag(CtH4> in C2H4, and (C) AuCCaH,) in C,H4 at 10-12K where dotted lines indicate correlations between corresponding "low-energy 6a i —> 3bj and "high-energy 5a i — 6a i excitations of M(CjH4), where M = Cu, Ag, Au. Lines ascribed to free Cu and Au atoms in the matrix are indicated with arrows 143, 148).

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