Diffusion miscibility, polymer

The solution of the resulting modified equation takes the form of a sharp front that moves into the polymer, not as the square root of time, but at a constant velocity. Ahead of this fi-ont is a small Fickian precursor, which may be detected by ion beam analysis techniques. This type of diffusion - known as case II diffusion - is very important and widespread for the case of penetration of glassy polymers by solvent. Analogous phenomena will take place when two miscible polymers are brought together, one of which is below its glass transition temperature and one above. Such situations are not difficult to realise in practice (Jabbari and Peppas 1995). 

Figure 4.25. (a) The mutual diffusion coefficient in the miscible polymer blend poly(vinyl chloride)-polycaprolactone (PVC-PCL) at 91 °C, as measured by x-ray microanalysis in the scanning electron microscope (Jones et al. 1986). The solid line is a fit assuming that the mutual diffusion coefficient is given by equation (4.4.11), with the composition dependence of the tracer diffusion coefficient of the PCL given by a combination of equations (4.4.9) and (4.4.10). The tracer diffusion coefficient of the PVC is assumed to be small in comparison, (b) The calculated profile of diffusion between pure PVC and pure PCL, on the basis of the concentration dependence of the mutual diffusion coefficient shown in (a). The reduced length u — where the... 

The determination of phase separation in partially miscible polymer blends by means of thermal analysis is often difficult because of the small demixing enthalpy and the slow rate of the diffusion-controlled process. Dreezen et al. (2001) smdied the phase separation of PEO/PES and PEO/Aramid blends by optical microscopy, conventional DSC and MTDSC. The onset of phase separation from optical microscopy corresponds very well to the onset of a small stepwise increase in the MTDSC heat capacity (Fig. 10.31). 

For miscible polymer systems with low values of diffusion coefficient, the polymers form lamellar structures with crisp material surfaces, that is, sheets of one polymer intimately intertwined in the other in a nested three-dimensional structure. The lamellar structures appear as alternating striations on a cross-sectional plane as in Figure 8.5a, with a characteristic striation thickness, s, which follows a distribution, defined as the striation thickness distribution [141]. A usual definition of striation thickness s is ... 

This is a three-part book with the first part devoted to polymer blends, the second to copolymers and glass transition tanperatme and to reversible polymerization. Separate chapters are devoted to blends Chapter 1, Introduction to Polymer Blends Chapter 2, Equations of State Theories for polymers Chapter 3, Binary Interaction Model Chapter 4, Keesome Forces and Group Solubility Parameter Approach Chapter 5, Phase Behavior Chapter 6, Partially Miscible Blends. The second group of chapters discusses copolymers Chapter 7, Polymer Nanocomposites Chapter 8, Polymer Alloys Chapter 9, Binary Diffusion in Polymer Blends Chapter 10, Copolymer Composition Chapter 11, Sequence Distribution of Copolymers Chapter 12, Reversible Polymerization. 

Ellipsometry is a powerful tool [16] for measuring the interfacial thickness between two polymers, whether in the case of immiscible or miscible polymer blends. In the case of miscible blends, investigations of changes in interfadal thickness with time at a fixed temperature allow the calculation of mutual diffusion coefficients [22]. In contrast, for immiscible blends the Flory-Huggins interadion parameter x can be deduced by measuring the interfacial thickness in an equilibrium state, and using the theory of Helfand [41] and its extended version [42]. 

Mutual Diffusion in the Miscible Polymer Blend Polystyrene ... 

MUTUAL DIFFUSION IN THE MISCIBLE POLYMER BLEND POLYSTYRENE.POLY (XYLENYL ETHER)... 

We have used forward recoil spectrometry to measure the mutual diffusion and tracer diffusion coefficients, D and D, in the miscible polymer blend of deuterated polystyrene (d-PS) poly(xylenyl ether) (PXE). Using the fast theory of mutual diffusion, D is related to the D, degree of polymerization N, and volume fraction of the individual blend components by,... 

In a miscible polymer blend, mutual diffusion measurements provide a very sensitive method for probing the thermodynamics of interaction between two chemically different segments. From the relationship between the transport coefficient Dt and the D s of the polymer components one can extract the Flory parameter X from the measured values of D and the D s. Upon rewriting Eq. 1, x is given by... 

Information on the monomeric friction coefficients of the constituent components in a miscible polymer blend is therefore vital for a better understanding of the rheological behavior (the dynamics) of miscible blends. Efforts to obtain such information have been reported by some investigators (Composto et al. 1990, 1992 Kim et al. 1994), who employed forward recoil spectrometry to measure the reptation (tracer) diffusion coefficients of the constituent components in a miscible polymer blend. Specifically, measurements of tracer diffusion coefficient (D ) allowed them to calculate monomeric friction coefficients using the following expression, which is based on the tube model (Kim et al. 1994) 3... 

The miscibility of a polymer blend depends on temperature and blend composition, making the investigation of the dynamic behavior of miscible polymer blends very challenging. Associated with the dynamics of miscible polymer blends is the mutual diffusion that, as in determining the self-diffusion coefficient in polymer melts and solutions presented in Chapter 4, can be discussed using molecular theory. Thermodynamic interactions and free-volume effects determine the mutual diffusivity in miscible polymer blends. 

Compatibilized blends with addition of nanoparticles can become an alternative for conventional compatibilized blends containing block copolymers. Addition of oragnoclays to polymer blend affects multiple features thermodynamic phase behavior of the blend, the kinetics of phase separation and also the morphology formed in the two-phase region. Hemmati et al. proved that incorporation of organoclay evidently enhances the miscibility of PE and ethylene-vinyl acetate [EVA] phases in the amorphous regions of nanocomposites. In addition, the studies revealed that nanofiller influences the diffusion of polymer chains, which contributes to... 

Polymers dynamics of polymer chains microviscosity free volume orientation of chains in stretched samples miscibility phase separation diffusion of species through polymer networks end-to-end macrocyclization dynamics monitoring of polymerization degradation... 

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