Shell-core model

In the presence of more than one space-separated set of molecules in the system and also when the exchange between the two subensembles is slow, the contributions of each 

Counterion (with ionic head groups only) 

With the above approximation, the anisotropy decay is given below 

the parallel and perpendicular pump-probe signals due to component i are denoted by 7 and 7, respectively, and the respective orientational correlation functions are given by C2(i). When the two components display a large separation of timescales for both their vibrational lifetimes and orientational dynamics, then the long-time anisotropy decay can be an accurate representation of the anisotropy of the slow component. However, bofii of the two components can be mixed at intermediate times, making interpretation complicated. In such a case, a model hke Eq. (17.3) can be invoked to extraet information about the orientational dynamies. 

Water in and around micelles, reverse micelles, and microemulsions 

Particles with useful properties can be obtained with lesser amounts of conducting polymer. 

There is technological interest concerning the use of composite particles in functional coatings, and a number of excellent reviews have been prepared on conductive nanocomposites [53-56]. Although the synthesis of composites always demands some entrapment (encapsulation) of polymers, the following sections will illustrate mainly the core-shell composite particles. These composite particles can be divided broadly into either organic-ICP or inorganic-ICP. 

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Sir Ernest Rutherford (1871-1937 Nobel Prize for chemistry 1908, which as a physicist he puzzled over) was a brilliant experimentalist endowed with an equal genius of being able to interpret the results. He recognized three types of radiation (alpha, beta, and gamma). He used scattering experiments with alpha radiation, which consists of helium nuclei, to prove that the atom is almost empty. The diameter of the atomic nucleus is about 10 000 times smaller than the atom itself. Furthermore, he proved that atoms are not indivisible and that in addition to protons, there must also be neutrons present in their nucleus. With Niels Bohr he developed the core-shell model of the atom. 

Core damage frequency (CDF), for nuclear power facilities, 17 540 Coreless induction furnaces, 12 309-311 Core level electron energy loss spectroscopy (CEELS), 24 74 Coremans, Paul, 11 398 Core-shell model, 14 464 Core-shell particles, in polymer blends, 20 354-355... 

Figure 2. Two morphological models used to describe the origin of the ionic SAXS maximum observed for Nafion (a) the modified hard-sphere model depicting interparticle scattering and (b) the depleted-zone core—shell model depicting intraparticle scattering. (Adapted with permission from ref 36. Copyright 1981 American Chemical Society.)...

On a finer level, spherical grains that have an average diameter of 11 A are seen. A section analysis, which consisted of a plot of image contrast intensity versus distance, indicated that there is a mean periodicity of around 49 A, which is close to the values of the SAXS Bragg spacing usually associated with intercluster distances. This, as well as other microscopic studies, favors the model of phase separation as opposed to the core—shell model as applied to the interpretation of scattering data. The hydrated... 

A core-shell model for positively charged complexes... 

Fig. 15 A core-shell model of PVCL-Co nanoparticles. (Adapted from Ref. [54])...

A series of block copolymers were studied by SANS in which the C02-philic PFOA block length was varied (16,600 < Mn (g/mol) < 61,100) and the C02-phobic polystyrene block was held constant (Mn = 3,700 g/mol). Fitting of the scattering curves to a core shell model predicts spherical structures with an average degree of association of 7 surfactant molecules per micelle. This value was constant for the series of materials as would be expected... 

The work of James and Piirtna and of Piirma et al. is important because, inter alia, it highlights the role of several commonly used surfactants (e.g., Triton X) as transfer agents. This discovery complicates the interpretation of many experimental results reported in the literature. Inclnded in this category is the rise in molecular weight with conversion in Interval II, used by Grancio and Williams (1970) as evidence for the core-shell model of latex particle morphology. 

Fig. 3 (A) SANS data for water-in-hexane microemulsions stabilized by d-DDAB. The simultaneous fit to the Schultz core-shell model and error bars on the data are shown (B) SANS data for water-in-hexane microemulsions stabilized by fi-DDAB. The simultaneous fit to the Schultz core-shell model and error bars on the data are shown. (Reproduced from Ref. l)...

A number of workers have suggested that emulsion polymerization may not occur homogeneously throughout a polymer particle but either at the particle surface [75] or within an outer monomer-rich shell surrounding an inner polymer-rich core [76]. The latter has been referred to as the shell or core-shell model. The latter model has been proposed to explobserved constant rate behavior up to about 60 percent conversion, which according to Eq. (6.232) requires [M] to be constant, and the considerable experimental evidence which indicates that emulsified monomer droplets (serving as monomer reservoirs) disappear at 25 to 30 percent conversion and the monomer concentration drops thereafter. 

According to the core-shell model, the growing particle is actually heterogeneous rather than homogeneous, and it consists of an expanding polymer-rich (monomer-starved) core surrounded by a monomer-rich (polymer-starved) outer spherical shell. It is the outer shell that serves as the major locus of polymerization and Smith-Ewart (on-off) mechanism prevails while virtually no polymerization occurs in the core because of its monomer-starved condition. Reaction within an outer shell or at the particle surface would be most likely to be operative for those polymerizations in which the polymer is insoluble in its own monomer or under conditions where the polymerization is diffusion-controlled such that a propagating radical cannot diffuse into the center of the particle. 

Figure 8. Two models describing the spatial organization of the ionic sites, a Two-phase model composed of ionic clusters (ion-rich regions) dispersed in a matrix of the intermediate ionic phase, which is composed of fluorocarbon chains and nonclustered ions. The ionic scattering maximum arises from an interparticle interference effect, reflecting an average intercluster distance S. b Core-shell model in which the ion-rich core is surrounded by an ion-poor shell composed mostly of perfluorocarbon chains. The core-shell particles are dispersed in the intermediate ionic phase. The scattering maximum arises from an interparticle interference effect, reflecting a short-range order distance S of the core-shell particle. Note that the crystalline region was not drawn in the model for the sake of simplification and that the shape of the core-shell particle may not necessarily be spherical.

Later the growth model developed for a neodymium catalyst system was applied for the butadiene polymerization in gas phase. The ideas concerning the initial polymerization stages are in agreement with a core—shell model .The subsequent polymerization stages correspond to the polymeric flow model . 

The scattering data thus corrected are solely due to the radial excess electron density of the particles. Fig. 14 displays the measured intensity (filled circles) of the polystyrene latex discussed in conjunction with Fig. 10. The solid line is the fit of the experimental data by a core-shell model and a slightly asymmetric size distribution ([46] see below) taken from the analysis by ultracentrifugation [87]. In terms of a Gaussian size distribution the polydispersity corresponds to a standard deviation of 4.2%. The thin shell having a higher electron density stems from the adsorbed surfactant used in the synthesis of the latex. This effect and its detection by SAXS will be discussed further below (see Sect. 4.4). 

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