Intrinsic deformation

Steric stabilization is another well-established method of stabilizing colloidal suspensions of submicron to micron size [23]. The particles are coated with a layer of adsorbed or grafted polymer chains that provides a steric repulsion of entropie origin and helps disperse the particles by counterbalancing van der Waals attraction (Fig. la). The polymeric nature of the adsorbed or grafted layer softens the interparticle interactions and makes the particles intrinsically deformable. Many polymer chain/particle combinations have been synthesized and studied, and are described in the literature. Several popular colloidal systems consist of silica particles covered with various polymers such as polydimethylsiloxane [24], stearyl alcohol [25], alkyl chains [26], and polyethylene oxide [27]. Polymethylmethacrylate and polystyrene particles grafted with polymer chains have also been used extensively. For a review on the impressive literature on the subject we refer the interested reader to Vlassopoulos and Fytas [2]. 

In the volume of silicon the precipitate produces a stress field caused by mismatch between the lattice parameters of precipitate (fl ) and the surrounding matrix (02) (Kolesnikova et al., 2007). Then, the intrinsic deformation of the precipitate is defined as described bellow... 

In general, the precipitate intrinsic deformation in the matrix volume can be expressed as follows... 

In respect of a spherical precipitate with equiaxial intrinsic deformation, the calculation of elastic fields of the precipitate is substantially simplified. Let us assume that the intrinsic elastic strain energy of the precipitate before and after the formation of a dislocation loop of mismatch remains constant. Then the criterion of nucleation loop of misfit... 

Schrauwen BAG, Janssen RPM, Govaert LE, Meijer HEH (2004) Intrinsic deformation behavior of semicrystalline polymers. Macromolecules 37 6069-6078 Schultz JM (1974) Polymer materials science. Prentice Hall, Englewood Cliffs, NJ Schultz JM (1984) Microstructural aspects of failure in semicrystalline polymers. Polym Eng Sci 24 770-785... 

Schrauwen BAG, Janssen RPM, Govaert LE, Meijer HEH. Intrinsic deformation behavior of semiciystalline polymers. Macromolecules 2004 37( 16) 6069-6078. 

Inspired by the intrinsic deformation nature of polymer melt, various proposals have been put forward to constmct particular structure in polymer blend, aiming at the achievement of excellent performance. One of the typical examples is the methodology of in situ micro/nanofibrillation, in which, under the process of melt extrusion-hot stretching-quenching, the spherical dispersion domains in situ deform into micro/nanofibrils, realizing the scalable achievement of in situ micro/nanofibrillar composites, accompanied with greatly improved mechanical... 

Figure 15 Left Intrinsic deformation behavior of PC in uniaxial compression. Right Intrinsic deformation under a constant true compressive stress.

Figure 16 Left Mode of failure of PC (ductile) and PS (brittle). Right Comparison of the intrinsic deformation behavior of PC and PS.

Figure 37 Intrinsic deformation behavior of PLLA. Left True stress versus strain. Right Yield stress versus strain rate. Temperature is 37 °C.

The morphological variance appears more important with chrysotile than with amphiboles. The intrinsic stmcture of chrysotile, its higher flexibiUty, and interfibnl adhesion (10) allow a variety of intermediate shapes when fiber aggregates are subjected to mechanical shear. Amphibole fibers are generally more britde and accommodate less morphological deformation during mechanical treatment. 

As we saw in Chapter 10, the stress required to make a crystalline material deform plastically is that needed to make the dislocations in it move. Their movement is resisted by (a) the intrinsic lattice resistance and (b) the obstructing effect of obstacles (e.g. dissolved solute atoms, precipitates formed with undissolved solute atoms, or other dislocations). Diffusion of atoms can unlock dislocations from obstacles in their path, and the movement of these unlocked dislocations under the applied stress is what leads to dislocation creep. 

Viscoelastic polymers essentially dominate the multi-billion dollar adhesives market, therefore an understanding of their adhesion behavior is very important. Adhesion of these materials involves quite a few chemical and physical phenomena. As with elastic materials, the chemical interactions and affinities in the interface provide the fundamental link for transmission of stress between the contacting bodies. This intrinsic resistance to detachment is usually augmented several folds by dissipation processes available to the viscoelastic media. The dissipation processes can have either a thermodynamic origin such as recoiling of the stretched polymeric chains upon detachment, or a dynamic and rate-sensitive nature as in chain pull-out, chain disentanglement and deformation-related rheological losses in the bulk of materials and in the vicinity of interface. 

As is true for macroscopic adhesion and mechanical testing experiments, nanoscale measurements do not a priori sense the intrinsic properties of surfaces or adhesive junctions. Instead, the measurements reflect a combination of interfacial chemistry (surface energy, covalent bonding), mechanics (elastic modulus, Poisson s ratio), and contact geometry (probe shape, radius). Furthermore, the probe/sample interaction may not only consist of elastic deformations, but may also include energy dissipation at the surface and/or in the bulk of the sample (or even within the measurement apparatus). Study of rate-dependent adhesion and mechanical properties is possible with both nanoindentation and... 

Elastic vs. viscoelastic w hen = 0, no visco-plastic deformation occurs, Eq. 4.25 gives the intrinsic strength of the interface. 

The MaxEnt method will always deflate deformation features by the (<80 ) ,1S corresponding to measurements error [39]. To obtain an empirical estimate of this intrinsic spread allowed by the noise, twenty noisy data sets were generated as in formula (31), and fitted with BUSTER using the fragment and NUP already described in the previous paragraph. 

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