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The phase behavior of gels of E40B10 in 0.2 mol dm-3 aqueous K2SO4 was studied as a function of temperature and concentration. E40B10 is a diblock copolymer of poly(oxyethylene) (E) and poly(oxybutylene) (B), where the subscripts denote the number of repeats. The phase of the material was characterized by both simultaneous rheology and small-angle X-ray scattering, (SAXS). Depending on polymer volume fraction in the range 23−38% a body-centered cubic (bcc) structure or a face-centered cubic (fcc) structure was observed at low temperature, and at high temperature a hexagonally packed rod structure was formed. The phase transitions were shown to be characterized by discontinuous changes in the values of the dynamic shear moduli. A bcc−fcc transition was observed at high concentration, the corresponding transition temperature increasing with increasing polymer concentration. The effects of reciprocating shear were shown to increase the degree of order, manifested as a sharpening of the diffraction peaks in the SAXS pattern. The dynamic moduli decreased rapidly on the application of oscillatory shear and recovered equally rapidly when the deformation ceased. The decrease in moduli was shown, via the SAXS patterns acquired simultaneously, to be correlated to structural changes within the gel.

The simultaneous time-resolved study of structure development and reaction kinetics during polymer processing is an experimental method that has great potential in developing a deeper understanding of the parameters that govern the formation of structure and therefore polymer properties. A combination of synchrotron radiation small-angle x-ray scattering and Fourier-transform infrared spectroscopy experiments have been performed on a series of model segmented block copolyurethanes. These studies confirm that the driving force for structure development in polyurethanes is the thermodynamics of phase separation rather than hydrogen bonding.

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Abstract:The mechanisms by which complicated structures assemble from atoms and/or molecules to macroscale entities are far from understood. Clear insights into the rules concerning complete assembly processes, whether they be organic, inorganic or hybrid organic ± inorganic, are of general use. Here, we report on the assembly of the tetrapropylammonium-containing (TPA) puresilica zeolite ZSM-5 (MFI), by monitoring in situ the processes that occur over scales spanning more than four orders of magnitude (0.17 nm ± 6 mm). The combination of wide-angle, small-angle and ultra-small-angle X-ray scattering (WAXS, SAXS and USAXS, respectively) allows the direct imaging of the assembly process of the hybrid material TPA-MFI. It is shown that 2.8 nm entities, comprised of TPA and silicate, function as primary building units that aggregate to form structures up to 10 nm in size, which in turn form viable nuclei that initiate the growth of zeolite crystals. The nucleation mechanism of TPA-MFI thus involves ordering initially on the nanometer scale, followed by order at larger scales derived from the primary building units. The primary building units are specific for the crystal structure formed. The sequential formation of order from small (primary units), to medium (nuclei), to large scales (crystals) is consistent with other assembly processes, such as the construction of biological entities.

A new instrument for simultaneous small-angle X-ray scattering and rheology experiments on soft solids is described. This device is based on a commercial rheometer with a shear sandwich geometry in which the sample is subjected to a planar oscillatory deformation. This instrument has been used for time-resolved small-angle X-ray scattering/rheology experiments at the Synchrotron Radiation Source, Daresbury Laboratory, England. The focus has been in particular on the effect of large-amplitude shearing on the orientation of cubic phases in gels of block copolymers formed in concentrated solutions, and on the bicontinuous cubic phase of a block copolymer melt. Representative results are presented for face-centred cubic (f.c.c.) and bodycentred cubic (b.c.c.) phases in gels of poly(oxyethylene)±poly(oxybutylene) diblock copolymers, and for the bicontinuous cubic`gyroid' structure in a poly-(ethylene-alt-propylene)±poly(dimethylsiloxane) diblock copolymer melt. The orientations of the micellar b.c.c. phases in the gels and the gyroid structure (belonging to the b.c.c. space group Ia " 3d) following large-amplitude shearing are shown to be the same, i.e. directionally oriented crystals are produced in both cases, in which (111) directions are oriented along the shear direction.

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