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The mechanisms of flow of a face-centred cubic micellar phase were investigated using small-angle X-ray scattering (SAXS)
for samples under either steady or oscillatory shear in two different geometries: Couette cell and planar shear sandwich.
The system studied was a gel formed by a poly(oxyethylene)–poly(oxypropylene) diblock copolymer in water. SAXS indicated that
under steady shear in a Couette cell, flow occurs via sliding of hexagonal close-packed (hcp) layers with a close-packed [110]
direction along the shear direction. Under oscillatory shear in the planar shear sandwich, coexistence between this orientation
and one in which the hcp layers are rotated by 30° (and flow is in a [211] direction) was observed; however, when subject
to oscillatory shear in the Couette cell, flow only occurred along a [110] direction. This observation of flow in a non-close-packed
direction may be due to alignment induced by the walls of the shear sandwich.
Received: 24 February 2001 Accepted: 21 March 2001 相似文献
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V. Castelletto I. W. Hamley P. Holmqvist C. Rekatas C. Booth J. G. Grossmann 《Colloid and polymer science》2001,279(7):621-628
The structure and flow behaviour of a micellar “cubic” phase is studied, using small-angle X-ray scattering (SAXS) and constant
stress rheometry on a poly(oxyphenylethylene)–poly(oxyethylene) diblock copolymer in water. The predominant structure is a
face-centred cubic (fcc) array of spherical micelles, which under shear undergoes layer sliding to give a scattering pattern
from stacked hexagonal close-packed layers. A detailed analysis of the SAXS data indicates the presence of a fraction of grains
with a structure distorted from a fcc phase. The additional reflections that characterize this structure can be indexed to
a rhombohedral unit cell, space group R3ˉm, with the same volume as the fcc unit cell. The rhombohedral unit cell corresponds to a cubic cell that has been “stretched”
along a [111] direction, and it is suggested that such a structure results from the gradient in shear velocity in the Couette
cell employed. Shearing at high shear rates leads to a “smearing out” of the reflections, but upon cessation of shear under
these conditions a highly oriented SAXS pattern is obtained, which confirms the persistence of rhombohedral ordering. The
shear-induced changes in orientation are correlated to a plateau observed in the stress plotted against shear rate, such a
plateau being a sign of inhomogeneous flow.
Received: 8 September 2000 Accepted: 29 November 2000 相似文献
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Ian W. Hamley 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(27):6984-7000
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We demonstrate nondestructive (lossless) fluorescent state detection of individual neutral atom qubits trapped in an optical lattice. The hyperfine state of the atom is measured with a 95% accuracy and an atom loss rate of 1%. Individual atoms are initialized and detected over 100 times before being lost from the trap, representing a 100-fold improvement in data collection rates over previous experiments. Microwave Rabi oscillations are observed with repeated measurements of one and the same single atom. 相似文献
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Low-molecular-weight gelators: elucidating the principles of gelation based on gelator solubility and a cooperative self-assembly model 总被引:1,自引:0,他引:1
Hirst AR Coates IA Boucheteau TR Miravet JF Escuder B Castelletto V Hamley IW Smith DK 《Journal of the American Chemical Society》2008,130(28):9113-9121
This paper highlights the key role played by solubility in influencing gelation and demonstrates that many facets of the gelation process depend on this vital parameter. In particular, we relate thermal stability ( T gel) and minimum gelation concentration (MGC) values of small-molecule gelation in terms of the solubility and cooperative self-assembly of gelator building blocks. By employing a van't Hoff analysis of solubility data, determined from simple NMR measurements, we are able to generate T calc values that reflect the calculated temperature for complete solubilization of the networked gelator. The concentration dependence of T calc allows the previously difficult to rationalize "plateau-region" thermal stability values to be elucidated in terms of gelator molecular design. This is demonstrated for a family of four gelators with lysine units attached to each end of an aliphatic diamine, with different peripheral groups (Z or Boc) in different locations on the periphery of the molecule. By tuning the peripheral protecting groups of the gelators, the solubility of the system is modified, which in turn controls the saturation point of the system and hence controls the concentration at which network formation takes place. We report that the critical concentration ( C crit) of gelator incorporated into the solid-phase sample-spanning network within the gel is invariant of gelator structural design. However, because some systems have higher solubilities, they are less effective gelators and require the application of higher total concentrations to achieve gelation, hence shedding light on the role of the MGC parameter in gelation. Furthermore, gelator structural design also modulates the level of cooperative self-assembly through solubility effects, as determined by applying a cooperative binding model to NMR data. Finally, the effect of gelator chemical design on the spatial organization of the networked gelator was probed by small-angle neutron and X-ray scattering (SANS/SAXS) on the native gel, and a tentative self-assembly model was proposed. 相似文献
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Self-assembly of Peptide nanotubes in an organic solvent 总被引:1,自引:0,他引:1
Krysmann MJ Castelletto V McKendrick JE Clifton LA W Hamley I Harris PJ King SM 《Langmuir : the ACS journal of surfaces and colloids》2008,24(15):8158-8162
The self-assembly of a modified fragment of the amyloid beta peptide, based on sequence Abeta(16-20), KLVFF, extended to give AAKLVFF is studied in methanol. Self-assembly into peptide nanotubes is observed, as confirmed by electron microscopy and small-angle X-ray scattering. The secondary structure of the peptide is probed by FTIR and circular dichroism, and UV/visible spectroscopy provides evidence for the important role of aromatic interactions between phenylalanine residues in driving beta-sheet self-assembly. The beta-sheets wrap helically to form the nanotubes, the nanotube wall comprising four wrapped beta-sheets. At higher concentration, the peptide nanotubes form a nematic phase that exhibits spontaneous flow alignment as observed by small-angle neutron scattering. 相似文献
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