Christopher M. Martin

Structure, rheology and shear alignment of Pluronic block copolymer mixtures

The structure and flow behaviour of binary mixtures of Pluronic block copolymers P85 and P123 is investigated by small-angle scattering, rheometry and mobility tests. Micelle dimensions are probed by dynamic light scattering. The micelle hydrodynamic radius for the 50/50 mixture is larger than that for either P85 or P123 alone, due to the formation of mixed micelles with a higher association number. The phase diagram for 50/50 mixtures contains regions of cubic and hexagonal phases similar to those for the parent homopolymers, however the region of stability of the cubic phase is enhanced at low temperature and concentrations above 40 wt%. This is ascribed to favourable packing of the mixed micelles containing core blocks with two different chain lengths, but similar corona chain lengths. The shear flow alignment of face-centred cubic and hexagonal phases is probed by in situ small-angle X-ray or neutron scattering with simultaneous rheology. The hexagonal phase can be aligned using steady shear in a Couette geometry, however the high modulus cubic phase cannot be aligned well in this way. This requires the application of oscillatory shear or compression.

In situ observation of homogeneous nucleation of nanosized zeolite A

The formation of zeolite A (LTA) in the presence of tetramethylammonium cations is studied using in situ small angle and wide angle X-ray scattering (SAXS/WAXS) techniques. The SAXS measurements show the formation of homogeneous precursors 10 nm in size prior to the crystallization of LTA which were consumed during the crystallization. The crystal size is estimated by fitting the SAXS patterns with an equation for a cubic particle, and it is revealed that the final crystal size of the LTA depends on the synthesis temperature. However, although such temperature dependence is noted for the final crystal size, the initial precursor particles size appears to be closely similar (ca. 10 nm) irrespective of the synthesis temperature.

Structural models of metastable phases occurring during the crystallization process of saturated/ unsaturated triacylglycerols

Isothermal crystallizations of saturated and mixed saturated/unsaturated triacylglycerols (TAGs) have been studied by simultaneous time-resolved small-angle and wide-angle X-ray scattering measurements (SAXS/WAXS). The projection of the electron density profile along the layer normal derived from the lamellar peaks of the α2-phase can be assembled from two types of molecular dimers initially formed in the liquid state. One dimer corresponds to a typical two-chain packing of TAGs and the other is formed by opposing molecules overlapping by their two-acyl-chain sides. This structure occurs only in triacylglycerols containing both saturated and unsaturated acyl chains. The structural organization of the α2-phase is analogous to smectic A interdigitated phases. In the particular case of 1,3-distearoyl-2-oleoyl-sn-glycerol, StOSt, the α2-phase can evolve into a mixture of two phases (α1 and γ) with double and triple (2L and 3L) chain packing, respectively. A calculation of X-ray scattering patterns for simulated structures of randomly packed three-chain and two-chain layers of StOSt (2L + 3L) reproduced the three diffuse scattering peaks observed in the experimental SAXS patterns.

Energy-dependent in-situ small-angle x-ray scattering study of nano-ceramics

Energy-dependent small-angle X-ray scattering (SAXS) measurements near the Zr–K absorption edge of a nano-scale alumina–zirconia–silicate ceramic are reported. The in situ experiments cover the temperature range from 250 to 725°C, during which the sol-gel prepared nano-particles consolidate and the glass matrix phase begins to soften, leading to a compaction of the ceramic. The dominant scattering mechanism changes from a surface-fractal type to a mass-fractal type linked to direct contact areas between nano-particles and matrix. The energy-dependent data identify the zirconium-bearing phase as dominant in the high-q range. The experimental data are placed in the context of recent advances in in situ anomalous small-angle X-ray scattering (ASAXS) and some experimental problems and solutions of near-edge scattering are discussed. Contents 1. Introduction 4 2. Anomalous small-angle scattering 4 3. Experimental 6 4. Results 7 5. Discussion 8 6. Conclusions and outlook 10 Acknowledgments 10 References 11 Subject  Index 12