Core-shell inclusions

New concepts combining micromechanical models with the macromechanics of composite bodies were able to explain experimental data and predict limits of mechanical properties. Proposed models were used as the link between micro-and macromechanics of the composite body. In the calculations, in addition to properties of the matrix and the filler, properties and spatial arrangement of the interphase have been included (5). This model allows for a prediction of the structure-property relationships in PP filled wifh randomly distributed core-shell inclusions with EIL shell. This is of a pivotal importance in an attempt to develop and manufacture materials tailored to a particular end-use application. 

Figure 11.1 Effects of EIL polarity on morphology of oovered core shell inclusions in PP matrix. (From Ref, 30, courtesy of Chapman Hall.)...

Jancar et al. (154) attempted to calculate the effect of a soft interphase on the stress field around and in the platelet shaped and fibrous inclusions of small aspect ratio. Because of the presence of a shear component of the stress in the interphase, a transfer of a portion of the load from the matrix to the core-shell inclusion is possible, even when the interphase layer has modulus of elasticity substantially lower than the matrix. At least five to six times thicker soft interphase compared with spherical inclusion is necessary to reduce the reinforcing efficiency of platelets with aspect ratio of 5 to a negligible value. Above the elastomer interphase volume fraction equal to about 12 vol% of the inclusions, the elastic modulus of the complex core-shell inclusion equals that of the PP matrix. 

In the case of core-shell inclusions with soft interphase thicker than 1% of the particle diameter, the yield strength can be calculated using the simple idea of reduction of the matrix cross-section as the cause of stress concentration as proposed for example by Nicolais and Narkis (161) in the case of nonadhering particles embedded in a polymer matrix. The lower bound for the composite yield strength can be written as ... 

This Hamiltonian is written only for a valence subspace of electrons which are treated explicitly and denoted by indices and jv In practice, this subspace is often extended by inclusion of some outermost core shells for better... 

In the past, nucleation fields such as Eq. (15) have been obtained for several cases spherical particles in an infinitely hard matrix [110], small inclusions in a matrix of arbitrary anisotropy and exchange stiffness [105] [111], various types of multilayers [111, 113], and some core-shell and nanowire configurations [105, 114, 115], For a discussion of the unphysical limit of very small inclusions, L = 0, see e.g. [5],... 

As for the linear properties, numerous approaches have been proposed to predict and explain the nonlinear optical response of nanocomposite materials beyond the hypothesis leading to the simple model presented above ( 3.2.2). Especially, Eq. (27) does not hold as soon as metal concentration is large and, a fortiori, reaches the percolation threshold. Several EMT or topological methods have then been developed to account for such regimes and for different types of material morphology, using different calculation methods [38, 81, 83, 88, 96-116]. Let us mention works devoted to ellipsoidal [99, 100, 109] or cylindrical [97] inclusions, effect of a shape distribution [110, 115], core-shell particles [114, 116], layered composites [103], nonlinear inclusions in a nonlinear host medium [88], linear inclusions in a nonlinear host medium [108], percolated media and fractals [101, 104-106, 108]. Attempts to simulate in a nonlinear EMT the influence of temperature have also been reported [107, 113]. 

Epoxy toughening additives initially were based on rubbery inclusions or functionalized oligomers (carboxy or amine terminated butadiene/ acrylonitrile copolymers). More recently, impact modifiers (core-shell type) similar to that commonly employed with PVC have been proposed. For composites, tougher epoxy matrix candidates... 

The scattering function describing the time-dependent scattering intensity of micelles in a KZAC experiment involves a time-dependent core-shell model where the contrast is a function of the fraction of chains exchanged, /exc- Here, we shall limit the discussion to cylindrical and spherical structures using simple A-B diblock copolymers as an example. Inclusion of other structures such as vesicles could be shghtly more comphcated because the microscopic composition might be potentially different in the inner and outer shells. 

Temperature and pH responsiveness has been also recorded for a non covalently bonded DHBC inclusion complex, namely P4VP-PNIPAM [33]. The non-covalently connected copolymer tends to create micelles with PNIPAM cores at low pH values and at elevated temperatures. However, at room temperature and high pH values, the polymer formed vesicles instead of core-shell micelles. The formation of vesicles was confirmed by a number... 

The shape or form of the particles is referred to as the particle morphology. Particles may be uniformly spherical, have core-shell morphologies (51, 263), be hemispherical (382), have domains or inclusions (349), be nonspherical or irregular in shape, or may be inverted (in which the core and shell compositions are reversed). Figure 5 illustrates some of the possible particle morphologies. The particular morphology is determined by thermodynamic (equilibrium) (67,101) and kinetic (rate of phase separation versus rate of polymerisahon) considerations. In some cases, latex... 

Inspired by the work of Liu and co-workers who have described a new kind of core-shell (sUica-PEG) nanoparticles as platform for dmg-delivery [71], we have very recently proposed [93] a synthetic strategy that affords monodispersed and ordered core-shell silica nanoparticles. Such systems allow the irreversible inclusion of dye molecules in the silica core and present a stable biocompatible and water soluble polymeric protective shell. For these reasons these materials appear particularly promising in the development of luminescent probes for in vitro and, hopefully, in vivo medical and bio-analytical applications. 

Toughness enhancement can be realized by homogeneous rubber particles, core-shell particles, or heterogeneous modifier particles in the so-called disperse systems. The rubber content varies usually between 5 and 30 wt.%. An alternative is a network arrangement of the rubber in inclusion systems or network systems. 

Hgure 5.3 Core-shell particles (rubber shells with PS inclusions and SAN grafted surfaces) OSO4 stained, UDS, TEM... 

---