External polymers, blend morphology

As previously mentioned, the quantity tc is governed by inner parameters of the system. When one considers morphology evolution in polymer blend solutions, tc has to be compared with the externally imposed pinning-down time tp after which no further phase changes occur. For blend solutions, the quantity tp is related to the rate of solvent evaporation. 

A mean field theory has recently been developed to describe polymer blend confined in a thin film (Sect. 3.2.1). This theory includes both surface fields exerted by two external interfaces bounding thin film. A clear picture of this situation is obtained within a Cahn plot, topologically equivalent to the profile s phase portrait d( >/dz vs < >. It predicts two equilibrium morphologies for blends with separated coexisting phases a bilayer structure for antisymmetric surfaces (each attracting different blend component, Fig. 32) and two-dimensional domains for symmetric surfaces (Fig. 31), both observed [94,114,115,117] experimentally. Four finite size effects are predicted by the theory and observed in pioneer experiments [92,121,130,172,220] (see Sect. 3.2.2) focused on (i) surface segregation (ii) the shape of an intrinsic bilayer profile (iii) coexistence conditions (iv) interfacial width. The size effects (i)-(iii) are closely related, while (i) and (ii) are expected to occur for film thickness D smaller than 6-10 times the value of the intrinsic (mean field) interfacial width w. This cross-over D/w ratio is an approximate evaluation, as the exact value depends strongly on the... 

The properties of the external surface can significantly alter phase separation in a thin polymer film. In extensive experimental investigations of the phase separation of polymer blends directed by patterned substrates [1,56,58,60,80-88] it was observed that the domain size evolved in a power law relation with time. The composition wave was normal to, and propagates inward from, the functionalized substrate. Likewise, processing parameters such as pattern size in the substrate were seen to affect refinement of the morphology. 

The biocatalysts obtained were evaluated with respect to the composition, morphology, activity and stability of the immobilised enzyme in the starch hydrolysis reaction. In general, two alternative methods can be used, considering the bioartificial matrix as a substrate for the enzyme (this method is used for example to drive drug release into erosion control devices), or alternatively, as in the case of this work, after blending the enzyme with a polymer, and investigating its activity against an external substrate. The apparent kinetic parameters of the reaction catalyzed by the immobilised and native enzymes were determined and compared. 

Figure 18.4 Effect of particle morphology on MFT (a) curves of polymer compositions in different morphology particles vs MFTs of onulsions for the MMA-BA system ( ) I BA/n MMA, ( ) blend, ( ) copolymer (b) curves of polymer compositions in gradient latex particles vs MFTs of emulsions for the A4MA-BA system ( ) from internally soft to externally hard, (A) from internally hard to externally soft, ( ) homogeneous copolymer latexes (c) curves of polymer compositions in different morphology particles vs MFTs of emulsions for the styrene-EA system ( ) blend, ( ) copolymer, (V) I EA/n styrene, (O) I styrene/n EA. (Reproduced with permission from Cao et al. f561.1...

Electronic impedance spectroscopy (EIS) is used to measure the polymer dielectric properties and the changes in these properties with exposure time. This is based on the interaction of an external field with the electric dipole moment of the sample, often expressed by permittivity. Dielectric thermal analysis (DETA) measures the permittivity, capacitance and dielectric loss of a polymer sample under an oscillating electric field as a function of temperature. The dielectric properties of a blend system in general depend on structure, crystallinity, morphology and additives. " ... 

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