Spinodal modulated structure

Thin films of blended deuterated polystyrene (dPS) and poly(vinyl methyl ether) (PVME) were imaged as a fimction of the dPS PVME ratio. Near the critical composition of 35% dPS, an imdulating, spinodal-like structure was observed, whereas for compositions away from the critical mixture ratio, regular mounds or holes (< dPS < < crit and < dPS > (pent, respectively) were present. These variations were assigned to surface tension effects (120). Blends of PBD, SBR, isobutylene-brominated p-methylstyrene, PP, PE, natural rubber, and isoprene-styrene-isoprene block rubbers were imaged (Fig. 18). Stiff, styrenic phases and rubbery core-shell phases were evident as the authors utilized force-modulated afm to determine detailed microstructure of blends, including those with fillers such as carbon-black and silica (121). 

For the case in which both ccr and cmo are within the spinodal region of an Fe-Cr-Mo ternary phase diagram, the ampUtude of Mo increases at the peak positions of Cr and the amplitude of Cr also increases at the peak positions of Mo. The wavelength of the modulated structure is shorter than those of Fe-Cr and Fe-Mo binary alloys. 

The authors themselves emphasize the two main Hmitations of this theory. The first Hmitation concerns the assumption of chemical quenching , i.e., that the polymerization kinetics and cross-finking are so rapid that any phase separation during the time needed for these processes is negligible. Their estimate of a typical time constant for the development of instability in the linear regime of spinodal decomposition, 10 s , shows that this limit may not be applicable to all cases of experimental interest. We cannot help accepting this statement. The second limitation is that their treatment does not allow us to describe the periodically modulated structures. 

The continuous sinusoidal composition change that occurs during spinodal decomposition can be considered to be a modulation of the solid structure. It is now known that many structures employ modulation in response to compositional or crystallographic variations, and in such cases the material flexibly accommodates changes without recourse to defect populations. (Other modulations, in, for example, magnetic moments or electron spins, although important, will not be discussed here.)... 

When a polymer solution is allowed to evaporate from a surface, dewetting instabilities can arise, producing modulated patterns like spinodal structures (68). Section IV addresses the applicability of these interesting phenomena to making opto-electronical devices. 

From the above mentioned results, it is expected that the morphology in the blends (50/50) of homo s-BPDA-PDA with PMDA-PDA ODA copolymer varies from inhomogeneous to homogeneous with increasing PDA content in the copolymers. In fact, the phase-contrast microscope observation indicated that a modulated phase structure formed by the spinodal decomposition in the blend film at PDA = 0... 

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