| 1. |
- Dintcheva, N. T., et al.
(författare)
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Rheological behavior of PAN-based electrolytic gel containing tetrahexylammonium and magnesium iodide for photoelectrochemical applications
- 2013
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Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 1435-1528 .- 0035-4511. ; 52:10-12, s. 881-889
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Tidskriftsartikel (refereegranskat)abstract
- Polymeric gel electrolyte systems have gained great interest in the last few years due to their suitability for the manufacturing of ionic devices, for example, for dye-sensitized solar cells (DSSCs). In this work, the rheological behavior at fixed temperatures and at fixed frequency of complex systems based on polyacrylonitrile (PAN) and plasticizers such as ethylene carbonate (EC) and propylene carbonate (PC) containing tetrahexylammonium (Hex(4)NI) and magnesium iodide (MgI2) was studied. These results for these PAN-EC-PC gels suggest a structural change of the "strong-to-weak" type at about 60 A degrees C and the beginning of the gel-sol transition at about 75 A degrees C. These transitions occur at higher temperatures for polymer electrolyte gels containing Hex(4)NI and even higher with MgI2, suggesting the possibility of post-factum treatments of the gels and of the DSSCs to improve their performance. The rheological results suggest that the progressive substitution of Hex(4)NI with MgI(2)leads to a significant improvement in the rheological behavior of the PAN-based electrolytic gel due to the decrease of the mobility of the macromolecules and probably to an increase of the interaction between the inorganic ions and the macromolecules. Moreover, when these gels were used in DSSCs, the sample containing 80(Hex(4)NI)/40(MgI2) showed the best performance considering its rheological and calorimetric behavior as well as energy conversation efficiency and short-circuit current density.
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| 2. |
- Djalili-Moghaddam, M., et al.
(författare)
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Fibre suspension rheology : Effect of concentration, aspect ratio and fibre size
- 2006
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Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 0035-4511 .- 1435-1528. ; 45:3, s. 315-320
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Tidskriftsartikel (refereegranskat)abstract
- Viscosity data for fibre suspensions are produced using cone-and-plate geometry of enhanced dimensions for the reduced influence of fibre-wall interactions. Semi-concentrated suspensions of monodisperse polyamide fibres in silicone oil, with a variety of fibre concentrations (2, 5 and 8%), lengths and diameters, were studied. The suspension viscosity was measured in a range of shear stress in order to study the stress dependence. The study here focuses on the nature of the forces and interactions that contribute to the suspension viscosity. The results show that at sufficiently high stress levels, the suspension viscosity tends to reach a steady-state. At very low stress levels the suspension viscosity increases over time, most likely due to structures formed by adhesive forces. At higher concentrations, the viscosity depends on the absolute size of the fibres, again indicating the presence of non-hydrodynamic interactions.
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| 3. |
- Djalili-Moghaddam, M, et al.
(författare)
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Study of geometry effects in torsional rheometry of fibre suspensions
- 2004
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Ingår i: Rheologica Acta. - : Springer-Verlag. - 0035-4511 .- 1435-1528. ; 44:44, s. 29-37
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Tidskriftsartikel (refereegranskat)abstract
- This work concerns the problem of measuring the viscosity of a suspension of fibres that are not short compared to the dimensions of the measurement device. We have examined various geometry effects in shear using parallel-plate and cone-and-plate configurations. Steady state viscosity, transient viscosity and first normal stress difference have been studied. Silicone oil with milled glass fibres at 8 vol.% was used as a model fibre suspension. The conventional parallel-plate geometry exhibits a significant gap dependence of the apparent viscous response. Too small gaps constrain the fibre rotations, thus lowering the initial stress peak and delaying the development of steady state. Too large gaps lead to a loss of liquid at the sample perimeter, which reduces the apparent steady state viscosity. The steady state response, however, seems to be correct for gaps in the range 1 - 2 mm when the maximum fibre length is 1.5 mm. The cone-and-plate geometry is less sensitive to large gaps. Too small a gap at the ( truncated) cone apex leads to anomalous response due to bridging of the gap by fibres. The use of unusually large plates ( 100 mm diameter) and different cone angles and truncations was explored. It was shown that cone-and-plate configurations of large diameter and large truncation can effectively decrease the geometry disturbances both due to fibre bridging at the cone apex and loss of liquid at the edge.
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| 4. |
- Djalili-Moghaddam, M., et al.
(författare)
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Study of geometry effects in torsional rheometry of fibre suspensionsIs The “Creative Class” Necessarily Urban?
- 2004
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Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 0035-4511 .- 1435-1528. ; 44:1, s. 29-37
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Tidskriftsartikel (refereegranskat)abstract
- This work concerns the problem of measuring the viscosity of a suspension of fibres that are not short compared to the dimensions of the measurement device. We have examined various geometry effects in shear using parallel-plate and cone-and-plate configurations. Steady state viscosity, transient viscosity and first normal stress difference have been studied. Silicone oil with milled glass fibres at 8 vol.% was used as a model fibre suspension. The conventional parallel-plate geometry exhibits a significant gap dependence of the apparent viscous response. Too small gaps constrain the fibre rotations, thus lowering the initial stress peak and delaying the development of steady state. Too large gaps lead to a loss of liquid at the sample perimeter, which reduces the apparent steady state viscosity. The steady state response, however, seems to be correct for gaps in the range 1-2 mm when the maximum fibre length is 1.5 mm. The cone-and-plate geometry is less sensitive to large gaps. Too small a gap at the (truncated) cone apex leads to anomalous response due to bridging of the gap by fibres. The use of unusually large plates (100 mm diameter) and different cone angles and truncations was explored. It was shown that cone-and-plate configurations of large diameter and large truncation can effectively decrease the geometry disturbances both due to fibre bridging at the cone apex and loss of liquid at the edge.
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| 5. |
- Drake, Birger, et al.
(författare)
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Food crushing sounds : An analytic approach
- 1974
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Ingår i: Rheologica Acta. - 0035-4511 .- 1435-1528. ; 13:3, s. 608-612
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Tidskriftsartikel (refereegranskat)abstract
- As a complement to the study of human mastication sounds, crushing sounds produced with a mechanical device were tape recorded and played back in such a way as to obtain acoustical line spectra for short intervals around the points of time when the sounds were loudest. The spectra were then evaluated to give measures calculated from amplitudes belonging to sets of such frequencies. These measures aimed at, e.g., estimating the width of the frequency band occupied by the major part of the sound, the two theoretically possible extremes being a pure tone and a "white noise". In a way, this analytical method results in discrete Fourier transforms. In studies with various brands of crisp bread it was found that the crushing sound differed in a reproducible way among the brands. The sounds, however, do not measure the same properties as ordinary rheological analyses. They can therefore be considered as a potential complement to flexure and compression data. © 1974 Dr. Dietrich Steinkopff Verlag.
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| 6. |
- Ericsson, K. A., et al.
(författare)
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Sliding plate rheometry of planar oriented concentrated fiber suspension
- 1997
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Ingår i: Rheologica Acta. - 0035-4511 .- 1435-1528. ; 36:4, s. 397-405
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Tidskriftsartikel (refereegranskat)abstract
- The rheology of concentrated planar fiber suspensions is investigated. A new experimental technique for fiber suspensions based on a sliding plate rheometer incorporating a shear stress transducer is developed. It is shown that this instrument works well for the tested material systems. The Theological behavior in steady shear is subsequently investigated. The results can be largely explained by a combination of frictional and hydrodynamic interaction. Despite this evidence of friction no yield stress could be detected for the investigated shear rates. It was also found that the fiber aspect ratio did not influence the steady shear viscosity.
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| 7. |
- Gomez-Martinez, Diana, et al.
(författare)
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Viscoelasticity and microstructure of a hierarchical soft composite based on nano-cellulose and kappa-carrageenan
- 2013
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Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 1435-1528 .- 0035-4511. ; 52:10-12, s. 823-831
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Tidskriftsartikel (refereegranskat)abstract
- Soft composites consisting of kappa-carrageenan gel interspersed with nano-cellulose were produced mimicking soft material structures. Microfibrillar cellulose (MFC) with a broad distribution of nano-fibre lengths was used as well as nano-crystalline cellulose (NCC) consisting of 20-nm nano-rods. The nano-fibre concentration, as well as the potassium ion concentration, was varied. The composites were characterized by rheology and light and electron microscopy. The incorporation of NCC into the carrageenan gel led to significant stiffening, and a sharp peak in the storage modulus occurred during gelation. This peak was not observed with MFC, which produced softer composites. An increase in the potassium concentration generally led to a more aggregated carrageenan structure with coarser network strands and increased modulus. By choosing suitable amount of nano-fibres and potassium concentration, soft composites with tailored properties could be produced.
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| 8. |
- Holm, Richard, et al.
(författare)
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Shear influence on fibre orientation : Dilute suspension in the near wall region
- 2007
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Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 0035-4511 .- 1435-1528. ; 46:5, s. 721-729
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this experimental work was to study the influence of shear close to a solid boundary on the fibre orientation in suspensions with different fibre aspect ratios and concentrations. We have studied a laminar suspension flow down an inclined plate. The fibre orientation in different wall parallel planes were measured. We applied an index-of-refraction (IR) matching method together with particle tracking techniques to obtain the fibre motion. The fibre orientation was extracted using a two-dimensional wavelet transform. The shear flow resulted in fibres perpendicularly oriented to the streamwise direction (rollers) in the near wall region. These rollers were observed in the experiment to perform a rolling-sliding motion down the inclined plate around a stable perpendicular orientation. As the distance to the wall increased the number of rollers decreased and the fibre orientation was unaffected from its initial streamwise orientation. As the aspect ratio increased the influence of shear on the fibre orientation decreased for all measured wall parallel planes. This was also the case for higher fibre concentrations. The purpose of this study was to contribute to the development of the capacity to control the sheet network structure in papermaking.
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| 9. |
- Jarahnejad, Mariam, et al.
(författare)
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Experimental investigation on viscosity of water-based Al2O3 and TiO2 nanofluids
- 2015
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Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 0035-4511 .- 1435-1528. ; 54:5, s. 411-422
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Tidskriftsartikel (refereegranskat)abstract
- This article investigates the influence of temperature, concentration, and size of nanoparticles, and addition of surfactants on dynamic viscosity of water-based nanofluids containing alumina (Al2O3) and titania (TiO2) nanoparticles. Two viscometers, a capillary and a falling ball, were used for the measurements in the temperature range of 20-50 A degrees C and the particle concentration of 3-14.3 wt.%. The results indicate that the viscosity of nanofluids is reduced by increasing the temperature, similar to their base fluids. Moreover, surfactants, which are used to improve the shelf stability of nanofluids, most likely increase their viscosity. The correlations derived from the linear fluid theory such as Einstein and Batchelor, especially for solid concentration above 1.5 wt.% are not accurate to predict viscosity of nanofluids, while the modified Krieger-Dougherty equation estimates viscosity of nanofluids with acceptable accuracy in a specific range of solid particle size to aggregate size.
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| 10. |
- Kádár, Roland, 1982, et al.
(författare)
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Nonlinear “oddities” at the percolation of 3D hierarchical graphene polymer nanocomposites
- 2020
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Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 1435-1528 .- 0035-4511. ; 59:5, s. 333-347
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Tidskriftsartikel (refereegranskat)abstract
- The nonlinear rheology of a novel 3D hierarchical graphene polymer nanocomposites was investigated in this study. Based on an isotactic polypropylene, the nanocomposites were prepared using simple melt mixing, which is an industrially relevant and scalable technique. The novel nanocomposites stand out as having an electrical percolation threshold (≈0.94 wt%) comparable to solution mixing graphene-based polymer nanocomposites. Their nonlinear flow behavior was investigated in oscillatory shear via Fourier-transform (FT) rheology and Chebyshev polynomial decomposition. It was shown that in addition to an increase in the magnitude of nonlinearities with filler concentration, the electrical percolation threshold corresponds to a unique nonlinear rheological signature. Thus, in dynamic strain sweep tests, the nonlinearities are dependent on the applied angular frequency, potentially detecting the emergence of a weakly connected network that is being disrupted by the flow. This is valid for both the third relative higher harmonic from Fourier-transform rheology, I3/1, as well as the third relative viscous, v3/1, Chebyshev coefficient. The angular frequency dependency comprised non-quadratic scaling in I3/1 with the applied strain amplitude and a sign change in v3/1. The development of the nonlinear signatures was monitored up to concentrations in the conductor region to reveal the influence of a more robust percolated network.
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