Polymers: Neutron Scattering

Higgins, Julia S.

doi:10.1016/b0-08-043152-6/01376-0

Cited by 298 publications

(483 citation statements)

References 4 publications

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“…For an open, three-dimensional network of linked rods or discs with a fixed volume fraction of subunits, a = 1/3. In the Q-range where the internal structure of an object is probed, the scattering is independent of z and a scaling argument [Higgins and Benoit 1994] may be used to show that the intensity, I(Q), decays as a power law:…”

Section: Discussion Of Q -3 Scattering and Crossover Pointsmentioning

confidence: 99%

Large scale structures in liquid crystal/clay colloids

Duijneveldt¹,

Klein²,

Leach³

et al. 2005

J. Phys.: Condens. Matter

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liquid crystal, colloid, SAXS Suspensions of three different clays in K15, a thermotropic liquid crystal have been studied by optical microscopy and small angle X -ray scattering. The three clays were Claytone AF, a surface treated natural montmorillonite, Laponite RD, a synthetic hectorite and mined Sepiolite. The Claytone and Laponite were sterically stabilized whereas Sepiolite formed a relatively stable suspension in K15 without any surface treatment. Micrographs of the different suspensions revealed that all three suspensions contained large scale structures. The nature of these aggregates was investigated using small angle X-ray scattering. For the clays with sheet-like particles, Claytone and Laponite, the flocs contain a mixture of stacked and single platelets. The basal spacing in the stacks was independent of particle concentration in the suspension and the phase of the solvent. The number of platelets in the stack and their percentage in the suspension varied with concentration and the aspect ratio of the platelets. The lath shaped Sepiolite did not show any tendency to organize into ordered structures. Here the aggregates are networks of randomly oriented single rods. [Pizzey 2004], particularly for platelets with a high aspect ratio, for example sterically stabilised montmorillonite particles. Small angle X-ray scattering (SAXS) revealed that these platelets dispersed in K15 (4-pentyl-4'-cyanobiphenyl) form stacks of 5±2 platelets with a basal layer spacing of 37Å independent of the temperature and concentration of the suspension. The spacing and stack size is however influenced by the host. The non-mesogenic host toluene favoured a higher percentage of single platelets and the stacks formed had on average two platelets with a basal layer spacing of 48Å. Particles with a smaller aspect ratio, for example sterically stabilised Laponite, a synthetic hectorite of 1 nm thickness and ~13 nm radius, seemed to delaminate almost completely in both solvents. Only 10% of the particles were found in stacks of 2±1 platelets with the same spacings as for montmorillonite, i.e. 37Å in K15 and 52±7 Å in toluene. The minimum scattering vector, Q, probed in these experiments was 0.03 Å -1 so it was not possible to determine whether the stacks and platelets were isolated or part of a larger aggregate. In this paper we report SAXS measurements extended to a lower Q range (0.003 Å -1 to 0.3 Å -1 ) to investigate the possibility of larger scale aggregation. The low Q was achieved using station 2.1 at the Daresbury Synchrotron Radiation Source [Daresbury] and beamline BM02 at the ESRF in Grenoble [Grenoble] rather than the laboratory based SAXS apparatus employed in the previous work. Furthermore, the high intensity of synchrotron radiation allowed short measurement times so that the flocculation could be monitored as a function of time. In addition results are presented on suspensions of Sepiolite, a naturally occurring clay consisting of lath shaped particles.

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Section: Discussion Of Q -3 Scattering and Crossover Pointsmentioning

confidence: 99%

Large scale structures in liquid crystal/clay colloids

Duijneveldt¹,

Klein²,

Leach³

et al. 2005

J. Phys.: Condens. Matter

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“…49 If such a system is first crosslinked into a network and subsequently subjected to a macroscopic strain, one can obtain information on the microscopic deformations of labeled random paths through the network. 49 In order to interpret the results, they need to be compared to the predictions of theories of rubber elasticity. Unfortunately, for randomly crosslinked networks it is quite difficult to calculate the relevant structure factors even in the simplest cases.…”

Section: Tube Modelsmentioning

confidence: 99%

Tube Models for Rubber−Elastic Systems

Mergell

Everaers

2001

Macromolecules

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In the first part of the paper we show that the constraining potentials introduced to mimic entanglement effects in Edward's tube model and Flory's constrained junction model are diagonal in the generalized Rouse modes of the corresponding phantom network. As a consequence, both models can formally be solved exactly for arbitrary connectivity using the recently introduced constrained mode model. In the second part, we solve a double tube model for the confinement of long paths in polymer networks which is partially due to crosslinking and partially due to entanglements. Our model describes a non-trivial crossover between the Warner-Edwards and the Heinrich-Straube tube models. We present results for the macroscopic elastic properties as well as for the microscopic deformations including structure factors.

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“…1,2 Due to the unique properties of the neutron, this technique has a number of advantages over alternative approaches and has been used to study both dynamic and thermodynamic behaviour. Among the disadvantages when studying mixtures, however, is the fact that the hydrogen atoms on one of the components usually have to be replaced with deuterium in order to achieve enough scattering intensity.…”

Section: Introductionmentioning

confidence: 99%

Effect of Deuterium Substitution on the Physical Properties of Polymer Melts and Blends

2010

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Using our simple lattice-based equation of state we capture the effect of deuterium substitution in polystyrene (PS), predicting both the pure component melt properties as well as the remarkable shift in the coexistence curve when hPS is replaced by dPS in forming a blend with poly(vinyl methyl ether) (PVME). Taking advantage of a rare opportunity to compare with experimental pure component data, we demonstrate that by characterizing the deuterated component through analysis of neutron scattering data we are able to make predictions for the pure dPS PVT properties which are in superb agreement with experiment. Calculations and measurement show that the dPS volume (per repeat unit) is slightly larger than that for hPS at low pressure, an effect which can be correlated with a difference in the model energetic parameter, (ε). In addition, we find that the dPS coefficient of thermal expansion (α) is larger than that for hPS and thus closer to the value for PVME. We propose that the increased similarity of the α's for dPS and PVME is connected to the increased miscibility of the dPS/PVME blend, a linkage which may be helpful to experimentalists in anticipating the potential effect on phase stability of polymer blends when deuterium substitution is employed.

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Polymers: Neutron Scattering

Cited by 298 publications

References 4 publications

Large scale structures in liquid crystal/clay colloids

Large scale structures in liquid crystal/clay colloids

Tube Models for Rubber−Elastic Systems

Effect of Deuterium Substitution on the Physical Properties of Polymer Melts and Blends

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