Flow of Colloidal Mesophases

University dissertation from Uppsala : Acta Universitatis Upsaliensis

Abstract: 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.

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