Ordering Of Microdomains Research Articles

Time-resolved small-angle x-ray-scattering study of ordering kinetics in diblock styrene-butadiene.

A detailed study of the kinetics of phase transformations of the diblock copolymer, styrene-butadiene, is reported. The technique of in situ time-resolved small-angle x-ray scattering with the use of synchrotron radiation has been used to study the first-order phase transitions of microphase separation and microdomain ordering. These transitions occur following a rapid, thermal quench from the homogeneous, disordered state to temperatures below the transition point. The isothermal ordering process is discussed in the context of classical theories of nucleation and growth. Anomalous temporal oscillations in the ordered-volume fraction are observed following quenches to temperatures just below the ordering transition. These results are reported and qualitatively discussed.

Effects of matrix polarity and ambient aging on the morphology of sulfonated polyurethane ionomers

Ethylene oxide units were incorporated into the backbone of Na+ sulfonated polyurethane ionomers in an attempt to induce aggregate dissociation at elevated, but observable, temperatures by reducing the incompatibility between ions and polymer. However, no dissociation could be observed by small-angle x-ray scattering (SAXS) before the onset of degradation, even when the polyol was pure EO. At 100°C and above, the SAXS patterns for all samples were quite similar, indicating morphological similarity. However, after annealing for several days at room temperature, two of the specimens appeared to develop a greater degree of microdomain order as evidenced by a narrowing of the main peak at q* and the development of a shoulder at 2q*x.

The effect of surface constraints on the ordering of block copolymer domains

The effect of surfaces on the ordering of block copolymer microdomains has been studied by TEM observation of thin-film droplets. Poly(styrene butadiene) block copolymers exhibiting spherical, cylindrical and lamellar microdomain morphologies were formed by solvent evaporation on a carbon substrate, annealed aboveT g, and stained with OsO4 prior to TEM observation. Samples with lamellar morphologies exhibited orientations of the lamellae in which the domains were either perpendicular to the substrate surface, or parallel to the substrate surface in which a layered structure resulted. Specimens in which cylinders were formed revealed sheets in which the cylinder axes lie parallel to the substrate, as well as parallel to each other. Stacking of such layers was observed, with exceptional registration between layers such that the cylinders in one layer were located over the inter-domain regions of the cylinders in adjacent layers. Specimens with spherical microdomain morphologies revealed a layer structure that consisted of hexagonally packed arrays of the spherical micelles. The stacking of layers of discrete thickness of all three types of microdomain morphology to produce the observed geometries indicates that the exterior of bulk samples may also exhibit such surface steps that reflect the ordering of the microdomains within the sample. Regardless of the microdomain type, all samples revealed a peripheral region in the thinnest area of the droplets in which the formation of the normal microdomain morphology (i.e. that of spheres, cylinders or lamellae) was inhibited. The uniform thickness of this region provides evidence that preferential segregation of the block component with the lowest surface energy takes place regardless of the sample composition.