| 1. |
- Dintcheva, N. T., et al.
(författare)
-
Rheological behavior of PAN-based electrolytic gel containing tetrahexylammonium and magnesium iodide for photoelectrochemical applications
- 2013
-
Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 1435-1528 .- 0035-4511. ; 52:10-12, s. 881-889
-
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.
|
|
| 2. |
- Djalili-Moghaddam, M., et al.
(författare)
-
Fibre suspension rheology : Effect of concentration, aspect ratio and fibre size
- 2006
-
Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 0035-4511 .- 1435-1528. ; 45:3, s. 315-320
-
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.
|
|
| 3. |
- Djalili-Moghaddam, M, et al.
(författare)
-
Study of geometry effects in torsional rheometry of fibre suspensions
- 2004
-
Ingår i: Rheologica Acta. - : Springer-Verlag. - 0035-4511 .- 1435-1528. ; 44:44, s. 29-37
-
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.
|
|
| 4. |
- Djalili-Moghaddam, M., et al.
(författare)
-
Study of geometry effects in torsional rheometry of fibre suspensionsIs The “Creative Class” Necessarily Urban?
- 2004
-
Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 0035-4511 .- 1435-1528. ; 44:1, s. 29-37
-
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.
|
|
| 5. |
- Drake, Birger, et al.
(författare)
-
Food crushing sounds : An analytic approach
- 1974
-
Ingår i: Rheologica Acta. - 0035-4511 .- 1435-1528. ; 13:3, s. 608-612
-
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.
|
|
| 6. |
- Ericsson, K. A., et al.
(författare)
-
Sliding plate rheometry of planar oriented concentrated fiber suspension
- 1997
-
Ingår i: Rheologica Acta. - 0035-4511 .- 1435-1528. ; 36:4, s. 397-405
-
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.
|
|
| 7. |
- Gomez-Martinez, Diana, et al.
(författare)
-
Viscoelasticity and microstructure of a hierarchical soft composite based on nano-cellulose and kappa-carrageenan
- 2013
-
Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 1435-1528 .- 0035-4511. ; 52:10-12, s. 823-831
-
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.
|
|
| 8. |
- Holm, Richard, et al.
(författare)
-
Shear influence on fibre orientation : Dilute suspension in the near wall region
- 2007
-
Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 0035-4511 .- 1435-1528. ; 46:5, s. 721-729
-
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.
|
|
| 9. |
- Jarahnejad, Mariam, et al.
(författare)
-
Experimental investigation on viscosity of water-based Al2O3 and TiO2 nanofluids
- 2015
-
Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 0035-4511 .- 1435-1528. ; 54:5, s. 411-422
-
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.
|
|
| 10. |
- Kádár, Roland, 1982, et al.
(författare)
-
Nonlinear “oddities” at the percolation of 3D hierarchical graphene polymer nanocomposites
- 2020
-
Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 1435-1528 .- 0035-4511. ; 59:5, s. 333-347
-
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.
|
|
| 11. |
- Meurer, Michael, et al.
(författare)
-
Nonlinear oscillatory shear tests of pressure-sensitive adhesives (PSAs) designed for transdermal therapeutic systems (TTS)
- 2021
-
Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 1435-1528 .- 0035-4511. ; 60:10, s. 553-570
-
Tidskriftsartikel (refereegranskat)abstract
- Transdermal therapeutic systems (TTS) based on pressure-sensitive adhesives (PSAs) allow for the application of pharmaceutical substances via diffusion through the skin. The rheological performance of PSA is largely investigated within small amplitude oscillatory shear (typically up to 1 %), although the skin motions exceed strains beyond 40 %. In this paper, amine-compatible (AC) and non-amine-compatible (NAC) silicone-based PSA compounds differing in the resin content were subjected to strain amplitude sweeps in a twin drive rheometer. Carreau-Yasuda-like fitting of storage and loss moduli curves intercepts the substantial effect of resin content on both compounds; up to four times higher, moduli of AC compounds were determined in SAOS, and their higher molecular mass combined with enhanced interactions contributed to an earlier transition to the nonlinear viscoelastic region. In the nonlinear range, elastic and viscous properties are affected by strains in a different manner with the trend favorable for the PSA application as TTS. The third relative higher harmonic from Fourier transformation I3/1 as well as intra-cycle strain stiffening and shear thickening ratios provide information relevant for an optimization of PSA subjected to large deformations.
|
|
| 12. |
- Naue, Ingo F.C., et al.
(författare)
-
High sensitivity measurements of normal force under large amplitude oscillatory shear
- 2018
-
Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 1435-1528 .- 0035-4511. ; 57:11, s. 757-770
-
Tidskriftsartikel (refereegranskat)abstract
- The two aims of this publication are to introduce a new and rheometer-independent rheometric tool for measuring the axial normal force in oscillatory shear rheology and to study the normal forces of polyolefin melts under large amplitude oscillatory shear (LAOS). A new plate geometry with an incorporated highly sensitive piezoelectric normal force sensor was designed for a rotational rheometer. The new geometry was used to investigate normal forces of polyethylene (PE) melts under LAOS. The resulting stress and normal force data was compared with the data from measurements in commercial high performance rotational rheometers. The stress and the normal force response were Fourier-transformed and their resulting spectra were analysed. The non-linear contributions to the FT-magnitude spectra (i.e. the intensities of the higher harmonics) were analysed using the framework of the Q-parameter, \(Q=I_{3/1}/{\gamma ^{2}_{0}}\) for both the stress spectrum and the normal force spectrum, resulting in the strain-dependent \(Q\left (\gamma _{0}\right )\) and \(Q_{NF}\left (\gamma _{0}\right )\), respectively. The newly designed normal force geometry had a sensitivity in the measurement starting from \(5\times 10^{-5}\) N up to 20 N, and respectively a signal-to-noise ratio (SNR) of \(1:\) 16.000, which is about a factor of 1.8 times better than the best performing commercial rheometers. The new geometry was used to determine \(Q\left (\gamma _{0}\right )\) and \(Q_{NF}\left (\gamma _{0}\right )\), to characterize the shear rheological behaviour of the PE melts. Even rather simple rheometers, those without normal force detection, can be extended utilizing the here presented tools for high sensitive FT-rheology analysing the normal forces.
|
|
| 13. |
- Nyström, Magda, 1984, et al.
(författare)
-
Extracting extensional properties through excess pressure drop estimation in axisymmetric contraction and expansion flows for constant shear viscosity, extension strain-hardening fluids
- 2016
-
Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 1435-1528 .- 0035-4511. ; 55:5, s. 373-396
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, hyperbolic contraction-expansion flow (HCF) devices have been investigated with the specific aim of devising new experimental measuring systems for extensional rheological properties. To this end, a hyperbolic contraction-expansion configuration has been designed to minimize the influence of shear in the flow. Experiments have been conducted using well-characterized model fluids, alongside simulations using a viscoelastic White-Metzner/FENE-CR model and finite element/finite volume analysis. Here, the application of appropriate rheological models to reproduce quantitative pressure drop predictions for constant shear viscosity fluids has been investigated, in order to extract the relevant extensional properties for the various test fluids in question. Accordingly, experimental evaluation of the hyperbolic contraction-expansion configuration has shown rising corrected pressure drops with increasing elastic behaviour (D e=0 similar to 16), evidence which has been corroborated through numerical prediction. Moreover, theoretical to predicted solution correspondence has been established between extensional viscosity and first normal stress difference. This leads to a practical means to measure extensional viscosity for elastic fluids, obtained through the derived pressure drop data in these HCF devices.
|
|
| 14. |
- Nyström, Magda, 1984, et al.
(författare)
-
Numerical simulations of Boger fluids through different contraction configurations for the development of a measuring system for extensional viscosity
- 2012
-
Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 1435-1528 .- 0035-4511. ; 51:8, s. 713-727
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports the flow behaviour of Newtonian and Boger fluids through various axisymmetric contraction configurations by means of numerical predictions. A principal aim has been to evaluate the geometrical design choice of the hyperbolic contraction flow. The FENE-CR model has been used to reflect the behaviour of Boger fluids, with constant shear viscosity, finite (yet large) extensional viscosity and less than quadratic first normal stress difference. Numerical calculations have been performed on six different contraction configurations to evaluate an optimized geometry for measuring extensional viscosity in uniaxial extensional flow. The influence of a sharp or rounded recess-corner on the nozzle has also been investigated. Few commercial measuring systems are currently available for measurement of the extensional rheology of medium-viscosity fluids, such as foods and other biological systems. In this context, a technique based on the hyperbolic contraction flow would be a suitable alternative. The pressure drop, the velocity field, the first normal stress difference and the strain rate across the geometry have each been evaluated for Newtonian and Boger fluids. This numerical study has shown that the hyperbolic configuration is superior to the other geometry choices in achieving a constant extension rate. In this hyperbolic configuration, no vortices are formed, the measuring range is broader and the strain rate is constant throughout the geometric domain, unlike in the alternative configurations tested. The difference between sharp and rounded recess-corner configurations proved to be negligible and a rise in excess pressure drop (epd) for increasing deformation rates has been observed.
|
|
| 15. |
- Shamu, John, 1990-, et al.
(författare)
-
Radial Flow Velocity Profiles of a Yield Stress Fluid between Smooth Parallel Disks
- 2020
-
Ingår i: Rheologica Acta. - : Springer Science and Business Media LLC. - 0035-4511 .- 1435-1528.
-
Tidskriftsartikel (refereegranskat)abstract
- In rock grouting, idealized 2D-radial laminar flow of yield stress fluids (YSF) is a fundamental flow configuration that is used for cement grout spread estimation. A limited amount of works have presented analytical and numerical solutions on the radial velocity profiles between parallel disks. However, to the best of our knowledge, there has been no experimental work that has presented measured velocity profiles for this geometry. In this paper, we present velocity profiles of Carbopol (a simple YSF), measured by pulsed ultrasound velocimetry within a radial flow model. We describe the design of the physical model and then present the measured velocity profiles while highlighting the plug-flow region and slip effects observed for three different apertures and volumetric flow rates. Although the measured velocity profiles exhibited wall slip, there was a reasonably good agreement with the analytical solution. We then discuss the major implications of our work on radial flow.
|
|
| 16. |
|
|
| 17. |
- Villone, Massimiliano M., et al.
(författare)
-
Numerical simulations of oscillatory shear flow of particle suspensions at finite inertia
- 2019
-
Ingår i: Rheologica Acta. - : Springer. - 0035-4511 .- 1435-1528. ; 58:11-12, s. 741-753
-
Tidskriftsartikel (refereegranskat)abstract
- We perform immersed-boundary-method numerical simulations of oscillatory shear flow of suspensions of mono-disperse non-colloidal rigid spherical particles in a Newtonian liquid from the dilute to the concentrated regime. Both small and large amplitude oscillatory shear flow (SAOS and LAOS, respectively) are studied and the effects of particle concentration, fluid inertia, particle-to-fluid density ratio, and deformation amplitude on the measured apparent viscoelastic moduli of the suspensions are quantified. In the SAOS regime, a non-zero storage modulus G '-values significantly change with inertia, but depend on the volume fraction of the solid phase only for suspensions of particles denser than the fluid. On the other hand, the loss modulus G '' increases with both inertia and particle concentration. In the LAOS regime, the moduli are only weakly dependent on the deformation amplitude for a dilute suspension, whereas non-monotonic variations are observed at high concentrations.
|
|
| 18. |
- Killander Cariboni, Carla
(författare)
-
La sceneggiatura teatrale inedita di “La Virtù di Checchina” : Discorso indiretto libero e modo iterativo nel transfer intermediale
- 2017
-
Ingår i: Revue Romane. - : John Benjamins Publishing Company. - 0035-3906. ; 52:2, s. 283-301
-
Tidskriftsartikel (refereegranskat)abstract
- This article deals with a comparison between Matilde Serao’s short story “Checchina’s Virtue” ( 1884 ) and the homonymous unpublished theatrical script written by Massimo Franciosa ( 1995 ), of which a summary is provided. The comparison between the source text and the adaptation draws on the debate about the narrativity of drama in which many scholars have engaged in the last decades: Richardson (1987) , Chatman (1990) , Jahn (2001) , Fludernik (2008) and Nünning & Sommer (2008) . The analysis focuses on two forms of diegetic narrativity that appear in the short story, i. e. free indirect discourse and the iterative mode, in order to see how the theatrical script deals with them. The analysis shows that the script preserves the narrative contents of the source text and highlights how diegetic and mimetic narrativity collaborate to the reworking and redistribution of those contents.
|
|
