Spinodal Mode

The location of the growth rate maximum and thus of the long spacing dac change with the crystallization temperature. As demonstrated by Fig. 4.23, dac shifts to larger values with increasing temperature and its dependence can be approximately described as 

The temperature Tc is located near to the equilibrium melting point of poly(ethylene terephthalate) dac,o is a limiting value of the long spacing, reached at the lowest temperatures. 

The second example concerns the crystallization of poly(vinylidene fluoride) (PVDF) during a melt spinning process. Extrusion of the melt through a 

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The intercept of the Q,q/q )/q plot is proportional to AT and the slope is independent of AT. Further, there is a cutoff wavevector qo delineating growing modes and decaying modes and qo is proportional to /AT. Therefore, if spinodal decomposition occurs, all of the following features must be simultaneously observed ... 

Linear Dynamics of Surface Mode Surface Spinodal Decomposition.114... 

Various modes of ordering are feasible. In systems with amphoteric cations (< .., Al34-), the fraction of Al3+ in tetrahedral or octahedral sites is a possible order parameter. Strain may lead to a bending of Si-O bonds. Periodic distributions of the components in space, along with elastic and/or electrostatic interactions, indicate spinodal ordering (demixing). Some examples will illustrate these general features. 

Microstructural characteristics of spinodal decomposition are periodicity and alignment. Periodicity arises from wavelengths associated with the fastest-growing initial mode. At later times, the characteristic periodic length increases due to microstructural coarsening. Periodicity can be detected by diffraction experiments. 

Without driving (a = 0) one has the typical scenario of spinodal decomposition and there is no anisotropy in the behavior of lx and ly (Fig. 23). Thus, small perturbations grow exponentially and at about t 15 (not shown) a nonlinear saturation of the fastest growing mode becomes important and sharp domain boundaries form. At about t 30 the late stage coarsening starts and the well-known scaling lx ly t1/3 is observed. In Fig. 24 snapshots of the phase separation process are presented for a particular run. 

Along with the traditional manner of the description of the chemical structure of linear copolymers by means of the hierarchy of probabilities P Uk of sequences of units Uk(k = 1,2,...), there is one more mode of the description of this structure. It is based on the consideration of the hierarchy of chemical correlation functions (so-called chemical correlators) (Kuchanov, 1978, 2000). The simplest among them, Yaj3(fc), has the meaning of probability to find two randomly chosen monomer units of types a and j3 divided along a macromolecule by any sequence Uk consisting of k units. This two-point correlator is of the utmost importance because its generating function enters into the expression for spinodal (Kuchanov,... 

The determination of the conformational and segregation properties of polymer brushes, created by diblock copolymers, has triggered their application to more complex problems. Diblock copolymers have been used to increase adhesion [277] or to eliminate the interfacial tension [256] between immiscible polymers. They may also modify the surface induced mode [116] and the bulk mode [278] of the spinodal decomposition observed in homopolymer blends. 

One of the most serious obstacles in the phase equilibrium studies of polymer blends is the viscosity of the system. At temperahires limited by the degradation the self-diffusion coefficient of macromolecules is of the order of magnitude 10 to 10 m /s [Kausch and Tirrell, 1989]. As a result the phase separation is slow. To accelerate the process a low speed centrifuge, the centrifugal homogenizer (CH), with PICS has been used [Koningsveld et al, 1982]. In short, centrifugation within the immiscibility zone permits determination of binodal and critical points, while the use of PICS mode allows location of the spinodal. 

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