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Alignment of Dispersions of Plate-Like Colloidal Particles of Ni(OH)(2) Induced by Elongational Flow
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
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2011 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 115, no 13, 3271-3280 p.Article in journal (Refereed) Published
Abstract [en]

Small-angle neutron scattering, SANS, has been used to study the alignment of a sterically stabilized colloidal dispersion of nickel hydroxide induced by elongational flow. Two different concentrations, 20 and 23 wt %, of well-defined hexagonal platelets have been studied. Significant anisotropy in the scattering patterns has been observed for the higher concentration dispersion that increases with increasing elongational strain rate. The effect of pipe flow (shear flow) on the orientational ordering at the inlets is also described. Near the outlets there is also a shear stress and this tends to increase the alignment. The orientational distribution of the particles under flow is described in terms of an order parameter calculated with respect to an individual director for each scattering pattern. The experimental measurements are supported by comparison with computer simulations which help to explain the effects of local velocity on the alignment induced by elongational flow. A slight decrease in the observed alignment was found after continuous flow for approximately 30 min and possible reasons are discussed.

Place, publisher, year, edition, pages
2011. Vol. 115, no 13, 3271-3280 p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-151969DOI: 10.1021/jp108805mISI: 000288885700001OAI: oai:DiVA.org:uu-151969DiVA: diva2:412617
Available from: 2011-04-26 Created: 2011-04-20 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Flow of Colloidal Mesophases
Open this publication in new window or tab >>Flow of Colloidal Mesophases
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This dissertation presents new work and results in the flow of complex fluids and experimental methodologies for their investigation. Plate-like colloidal particles of kaolinite and nickel hydroxide are studied. A study of lamellar fragments and their mixture with the nickel hydroxide particles is also presented. The lamellar fragments are self-assembled structures of surfactant molecules that approximate disks.

Particles are seen to align with their large faces parallel to the flow direction under shear and elongational strains. Order parameters have been calculated to quantify the extent of preferential alignment and direction of orientation. The experimental data are supported by comparisons with finite-element fluid mechanics calculations that provide estimates of the flow patterns and the strain rates. Elongational strain rates in the range of 5 − 20 s−1 are required to induce a high degree of alignment with the various sizes of the particles whereas about two to three order of magnitude higher shear strain rates are required. The combination of both elongational and shear strain is an effective means to provide a uniform alignment. Comparison of the Peclet numbers calculated for both the shear and elongational flow are presented and this explains that alignment occurs when the energy per particle of the strain is larger than the thermal energy. Mixtures have shown complex behavior: significant changes in the structure are observed that are not seen to the same extent in samples at rest.

X-ray diffraction and small-angle neutron scattering techniques are used to characterize the samples and determine the structure in flowing systems. Laboratory X-ray diffraction can be used to characterize dispersed samples. The combination of dynamic light scattering and X-ray diffraction was used to estimate the thickness of the stabilizing layers of the polymer on the colloidal particles. Scattering of synchrotron radiation and neutrons are powerful complementary techniques to provide information about flow and the potential to apply them to systems that are beyond the scope of simple simulations has been demonstrated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 45 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 838
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-152872 (URN)978-91-554-8101-8 (ISBN)
Public defence
2011-06-14, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
Opponent
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Available from: 2011-05-24 Created: 2011-05-02 Last updated: 2011-07-01Bibliographically approved

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Rennie, Adrian R.

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