The Experts below are selected from a list of 165 Experts worldwide ranked by ideXlab platform
A K Sood - One of the best experts on this subject based on the ideXlab platform.
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Experimental signatures of a nonequilibrium phase transition near the crossover point of a Langmuir monolayer.
Journal of physics. Condensed matter : an Institute of Physics journal, 2019Co-Authors: Pradip K. Bera, Rema Krishnaswamy, A. K. Kandar, A K SoodAbstract:We investigate the response of the two-dimensional (2D) continuous non-particulate film of surfactant Sorbitan Tristearate confined at the air-water interface under oscillatory shear deformation. The time dependence of various rheological parameters show critical-like behavior at a value of strain amplitude close to the crossover point of elastic ([Formula: see text]) and viscous ([Formula: see text]) shear moduli. Imposing oscillatory shear of different strain amplitudes ([Formula: see text]) above and below the crossover strain amplitude ([Formula: see text]) over a large number of cycles, we quantify the temporal dependence of interfacial viscous modulus, phase angle ([Formula: see text]) as well as higher harmonic components of stress. The number of shear cycles ([Formula: see text]) required for these quantities to reach the steady state value diverges near [Formula: see text]. The steady state values of the third harmonic ([Formula: see text]) show order parameter like behavior indicating the importance of higher order harmonics near the nonequilibrium transition. We further show that the energy dissipation per cycle per unit volume has a marked change near [Formula: see text], consistent with continuum level nonequilibrium shear-transformation-zone model of amorphous viscoplasticity.
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Shear banding in a yield stress bearing Langmuir monolayer
Soft Matter, 2011Co-Authors: Sayantan Majumdar, Rema Krishnaswamy, A K SoodAbstract:We examine the shear-thinning behaviour of a two dimensional yield stress bearing monolayer of Sorbitan Tristearate at air/water interface. The flow curve consists of a linear region at low shear stresses/shear rates, followed by a stress plateau at higher values. The velocity profile obtained from particle imaging velocimetry indicates that shear banding occurs, showing coexistence of the fluidized region near the rotor and solid region with vanishing shear-rate away from the rotor. In the fluidized region, the velocity profile, which is linear at low shear rates, becomes exponential at the onset of shear-thinning, followed by a time varying velocity profile in the plateau region. At low values of constant applied shear rates, the viscosity of the film increases with time, thus showing aging behaviour like in soft glassy three-dimensional (3D) systems. Further, at the low values of the applied stress in the yield stress regime, the shear-rate fluctuations in time show both positive and negative values, similar to that observed in sheared 3D jammed systems. By carrying out a statistical analysis of these shear-rate fluctuations, we estimate the effective temperature of the soft glassy monolayer using the Galavatti-Cohen steady state fluctuation relation.
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nonlinear viscoelasticity of Sorbitan Tristearate monolayers at liquid gas interface
Langmuir, 2007Co-Authors: Rema Krishnaswamy, Sayantan Majumdar, A K SoodAbstract:The interfacial rheology of Sorbitan Tristearate monolayers formed at the liquid/air interface reveal a distinct nonlinear viscoelastic behavior under oscillatory shear usually observed in many 3D metastable complex fluids with large structural relaxation times. At large strain amplitudes (γ), the storage modulus (G‘) decreases monotonically whereas the loss modulus (G‘ ‘) exhibits a peak above a critical strain amplitude before it decreases at higher strain amplitudes. The power law decay exponents of G‘ and G‘ ‘ are in the ratio 2:1. The peak in G‘ ‘ is absent at high temperatures and low concentration of Sorbitan Tristearate. Strain-rate frequency sweep measurements on the monolayers do indicate a strain-rate dependence on the structural relaxation time. The present study on Sorbitan Tristearate monolayers clearly indicates that the nonlinear viscoelastic behavior in 2D Langmuir monolayers is more general and exhibits many of the features observed in 3D complex fluids.
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Nonlinear viscoelasticity of Sorbitan Tristearate monolayers at liquid/gas interface.
Langmuir : the ACS journal of surfaces and colloids, 2007Co-Authors: Rema Krishnaswamy, Sayantan Majumdar, A K SoodAbstract:The interfacial rheology of Sorbitan Tristearate monolayers formed at the liquid/air interface reveal a distinct nonlinear viscoelastic behavior under oscillatory shear usually observed in many 3D metastable complex fluids with large structural relaxation times. At large strain amplitudes (γ), the storage modulus (G‘) decreases monotonically whereas the loss modulus (G‘ ‘) exhibits a peak above a critical strain amplitude before it decreases at higher strain amplitudes. The power law decay exponents of G‘ and G‘ ‘ are in the ratio 2:1. The peak in G‘ ‘ is absent at high temperatures and low concentration of Sorbitan Tristearate. Strain-rate frequency sweep measurements on the monolayers do indicate a strain-rate dependence on the structural relaxation time. The present study on Sorbitan Tristearate monolayers clearly indicates that the nonlinear viscoelastic behavior in 2D Langmuir monolayers is more general and exhibits many of the features observed in 3D complex fluids.
Lireny Aparecida Guaraldo Gonçalves - One of the best experts on this subject based on the ideXlab platform.
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Structural characteristics of crystals formed in palm oil using Sorbitan Tristearate and sucrose stearate
International Journal of Food Properties, 2018Co-Authors: Maria Aliciane Fontenele Domingues, Thais Lomonaco Teodoro Da Silva, Ana Paula Badan Ribeiro, Ming Chih Chiu, Lireny Aparecida Guaraldo GonçalvesAbstract:ABSTRACTThe formation and stabilization of fat crystals in palm oil (PO) by the templating effects of Sorbitan Tristearate (STS) and sucrose stearate (S-370) were examined. We observed that the cry...
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Sorbitan and sucrose esters as modifiers of the solidification properties of zero trans fats
LWT - Food Science and Technology, 2015Co-Authors: Maria Aliciane Fontenele Domingues, Ana Paula Badan Ribeiro, Ming Chih Chiu, Lireny Aparecida Guaraldo GonçalvesAbstract:Crystallization is the most important physical problem encountered in the industrial use of fats and oils. In this context, the objective of the present study was to analyze the action of Sorbitan Tristearate (STS) and sucrose stearate (SE) as potential modifiers of crystallization of the unsaturated triacylglycerols and to evaluate their effects on the physical properties of zero trans fat from soybean oil and fully hydrogenated soybean oil. The zero trans fat was obtained via chemical interesterification of a blend of soybean oil (70 g/100 g) and fully hydrogenated soybean oil (30 g/100 g). Samples containing 1 g/100 g, 3 g/100 g, and 5 g/100 g STS or SE were prepared and their crystallization properties were evaluated on the basis of the solid fat content (SFC), melting point, consistency, microstructure and visualization of the three-dimensional crystalline network. Both emulsifiers contributed to SFC adequacy, enhancing the consistency of the fat. As for compatibility, both emulsifiers were compatible with the interesterified fat. This was confirmed by the change in linearity of the curves at 15–20 °C. Samples with STS presented higher fractal dimension, indicating greater organization of the crystal lattice. Similarly, the visualization of three-dimensional crystalline network showed firmer structures for samples with STS compared with the samples SE.
Erich J. Windhab - One of the best experts on this subject based on the ideXlab platform.
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Sorbitan Tristearate layers at the air/water interface studied by shear and dilatational interfacial rheology.
Langmuir : the ACS journal of surfaces and colloids, 2005Co-Authors: Philipp Erni, Peter Fischer, Erich J. WindhabAbstract:The shear and dilatational rheology of condensed interfacial layers of the water-insoluble surfactant Sorbitan Tristearate at the air/water interface is investigated. A new interfacial shear rheometer allows measurements in both stress- and strain-controlled modes, providing comprehensive interfacial rheological information such as the interfacial dynamic shear moduli, the creep response to a stress pulse, the stress relaxation response to a strain step, or steady shear curves. Our experiments show that the interfacial films are both viscoelastic and brittle in nature and subject to fracture at small deformations, as was supported by in-situ Brewster angle microscopy performed during the rheological experiments. Although any large-deformation test is destructive to the sample, it is still possible to study the linear viscoelastic regime if the deformations involved are controlled carefully. Complementary results for the dilatational rheology in area step compression/expansion experiments are reported. The dilatational behavior is predominantly elastic throughout the frequency spectrum measured, whereas the layers exhibit generalized Maxwell behavior in shear mode within a deformation frequency regime as narrow as two decades, indicating the presence of additional relaxation mechanisms in shear as opposed to expansion/compression. If the transient rheological response from stress relaxation experiments is considered, then the data can be described well with a stretched exponential model both in the shear and dilatational deformations.
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Sorbitan Tristearate layers at the air water interface studied by shear and dilatational interfacial rheology
Langmuir, 2005Co-Authors: Philipp Erni, Peter Fischer, Erich J. WindhabAbstract:The shear and dilatational rheology of condensed interfacial layers of the water-insoluble surfactant Sorbitan Tristearate at the air/water interface is investigated. A new interfacial shear rheometer allows measurements in both stress- and strain-controlled modes, providing comprehensive interfacial rheological information such as the interfacial dynamic shear moduli, the creep response to a stress pulse, the stress relaxation response to a strain step, or steady shear curves. Our experiments show that the interfacial films are both viscoelastic and brittle in nature and subject to fracture at small deformations, as was supported by in-situ Brewster angle microscopy performed during the rheological experiments. Although any large-deformation test is destructive to the sample, it is still possible to study the linear viscoelastic regime if the deformations involved are controlled carefully. Complementary results for the dilatational rheology in area step compression/expansion experiments are reported. The dilatational behavior is predominantly elastic throughout the frequency spectrum measured, whereas the layers exhibit generalized Maxwell behavior in shear mode within a deformation frequency regime as narrow as two decades, indicating the presence of additional relaxation mechanisms in shear as opposed to expansion/compression. If the transient rheological response from stress relaxation experiments is considered, then the data can be described well with a stretched exponential model both in the shear and dilatational deformations.
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Rheology of gas/liquid and liquid/liquid interfaces with aqueous and biopolymer subphases
Mesophases Polymers and Particles, 2004Co-Authors: Philipp Erni, Peter Fischer, Erich J. Windhab, Victor Kusnezov, Patrick Heyer, Jorg LaugerAbstract:The stability, performance and quality of multiphase fluid products such as emulsions or foams are strongly influenced by the structure and rheology of the interfacial film between two immiscible liquids or between air and a liquid. In this study, an interfacial shear rheometer for both stress- and strain-controlled measurements at liquid/liquid and gas/liquid interfaces is used to study the interfacial rheology of the water-insoluble surfactant Sorbitan Tristearate. The subphase is either pure water or an aqueous viscous solution of κ-carrageenan. Air/water and air/solution as well as oil/solution interfaces with different bulk viscosity ratios are investigated. Experiments were performed in steady and oscillatory shear, as well as in stress relaxation (strain step) and creep recovery (stress pulse) mode. A setup combining interfacial rheometry with Brewster-angle microscopy (BAM) is presented and used for real-time imaging of the gas/liquid interface during rheological experiments. The problem of fracture in interfacial films during shear flow even at small deformations is addressed using both interfacial rheometry and BAM images.
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Interfacial Rheology of Gas/Liquid and Liquid/Liquid Interfaces
2004Co-Authors: Philipp Erni, Peter Fischer, Erich J. WindhabAbstract:An interfacial shear rheometer for stressand strain-controlled measurements at liquid interfaces is outlined. Experimental data are reported for the surfactant Sorbitan Tristearate on κ-carrageenan subphases. A setup combining interfacial rheometry with Brewster-angle Microscopy for realtime imaging of the interface is presented.
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stress and strain controlled measurements of interfacial shear viscosity and viscoelasticity at liquid liquid and gas liquid interfaces
Review of Scientific Instruments, 2003Co-Authors: Philipp Erni, Peter Fischer, Erich J. Windhab, Victor Kusnezov, Heiko Stettin, Jorg LaugerAbstract:An interfacial rheometer for both stress- and strain-controlled measurements of shear rheological properties at liquid/liquid and gas/liquid interfaces is presented. The device is based on a rotating or oscillating biconical bob design in combination with a low friction electronically commutated motor system. The interfacial shear stress, viscosity, and dynamic moduli are obtained by solving the Stokes equations (low Reynolds number) along with the Boussinesq–Scriven interfacial stress tensor, which is used for the boundary conditions at the interface. An improved and simple numerical method for the calculation of the velocity distribution in the measuring cell is presented. The scope and limitations of the rheometer are discussed. Results from steady shear and oscillatory experiments as well as creep recovery and stress relaxation tests at both oil/water and air/water interfaces with adsorbed films of a globular protein (ovalbumin) and spread films of a surfactant (Sorbitan Tristearate) are presented.
Rema Krishnaswamy - One of the best experts on this subject based on the ideXlab platform.
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Experimental signatures of a nonequilibrium phase transition near the crossover point of a Langmuir monolayer.
Journal of physics. Condensed matter : an Institute of Physics journal, 2019Co-Authors: Pradip K. Bera, Rema Krishnaswamy, A. K. Kandar, A K SoodAbstract:We investigate the response of the two-dimensional (2D) continuous non-particulate film of surfactant Sorbitan Tristearate confined at the air-water interface under oscillatory shear deformation. The time dependence of various rheological parameters show critical-like behavior at a value of strain amplitude close to the crossover point of elastic ([Formula: see text]) and viscous ([Formula: see text]) shear moduli. Imposing oscillatory shear of different strain amplitudes ([Formula: see text]) above and below the crossover strain amplitude ([Formula: see text]) over a large number of cycles, we quantify the temporal dependence of interfacial viscous modulus, phase angle ([Formula: see text]) as well as higher harmonic components of stress. The number of shear cycles ([Formula: see text]) required for these quantities to reach the steady state value diverges near [Formula: see text]. The steady state values of the third harmonic ([Formula: see text]) show order parameter like behavior indicating the importance of higher order harmonics near the nonequilibrium transition. We further show that the energy dissipation per cycle per unit volume has a marked change near [Formula: see text], consistent with continuum level nonequilibrium shear-transformation-zone model of amorphous viscoplasticity.
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Shear banding in a yield stress bearing Langmuir monolayer
Soft Matter, 2011Co-Authors: Sayantan Majumdar, Rema Krishnaswamy, A K SoodAbstract:We examine the shear-thinning behaviour of a two dimensional yield stress bearing monolayer of Sorbitan Tristearate at air/water interface. The flow curve consists of a linear region at low shear stresses/shear rates, followed by a stress plateau at higher values. The velocity profile obtained from particle imaging velocimetry indicates that shear banding occurs, showing coexistence of the fluidized region near the rotor and solid region with vanishing shear-rate away from the rotor. In the fluidized region, the velocity profile, which is linear at low shear rates, becomes exponential at the onset of shear-thinning, followed by a time varying velocity profile in the plateau region. At low values of constant applied shear rates, the viscosity of the film increases with time, thus showing aging behaviour like in soft glassy three-dimensional (3D) systems. Further, at the low values of the applied stress in the yield stress regime, the shear-rate fluctuations in time show both positive and negative values, similar to that observed in sheared 3D jammed systems. By carrying out a statistical analysis of these shear-rate fluctuations, we estimate the effective temperature of the soft glassy monolayer using the Galavatti-Cohen steady state fluctuation relation.
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nonlinear viscoelasticity of Sorbitan Tristearate monolayers at liquid gas interface
Langmuir, 2007Co-Authors: Rema Krishnaswamy, Sayantan Majumdar, A K SoodAbstract:The interfacial rheology of Sorbitan Tristearate monolayers formed at the liquid/air interface reveal a distinct nonlinear viscoelastic behavior under oscillatory shear usually observed in many 3D metastable complex fluids with large structural relaxation times. At large strain amplitudes (γ), the storage modulus (G‘) decreases monotonically whereas the loss modulus (G‘ ‘) exhibits a peak above a critical strain amplitude before it decreases at higher strain amplitudes. The power law decay exponents of G‘ and G‘ ‘ are in the ratio 2:1. The peak in G‘ ‘ is absent at high temperatures and low concentration of Sorbitan Tristearate. Strain-rate frequency sweep measurements on the monolayers do indicate a strain-rate dependence on the structural relaxation time. The present study on Sorbitan Tristearate monolayers clearly indicates that the nonlinear viscoelastic behavior in 2D Langmuir monolayers is more general and exhibits many of the features observed in 3D complex fluids.
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Nonlinear viscoelasticity of Sorbitan Tristearate monolayers at liquid/gas interface.
Langmuir : the ACS journal of surfaces and colloids, 2007Co-Authors: Rema Krishnaswamy, Sayantan Majumdar, A K SoodAbstract:The interfacial rheology of Sorbitan Tristearate monolayers formed at the liquid/air interface reveal a distinct nonlinear viscoelastic behavior under oscillatory shear usually observed in many 3D metastable complex fluids with large structural relaxation times. At large strain amplitudes (γ), the storage modulus (G‘) decreases monotonically whereas the loss modulus (G‘ ‘) exhibits a peak above a critical strain amplitude before it decreases at higher strain amplitudes. The power law decay exponents of G‘ and G‘ ‘ are in the ratio 2:1. The peak in G‘ ‘ is absent at high temperatures and low concentration of Sorbitan Tristearate. Strain-rate frequency sweep measurements on the monolayers do indicate a strain-rate dependence on the structural relaxation time. The present study on Sorbitan Tristearate monolayers clearly indicates that the nonlinear viscoelastic behavior in 2D Langmuir monolayers is more general and exhibits many of the features observed in 3D complex fluids.
Philipp Erni - One of the best experts on this subject based on the ideXlab platform.
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Sorbitan Tristearate layers at the air/water interface studied by shear and dilatational interfacial rheology.
Langmuir : the ACS journal of surfaces and colloids, 2005Co-Authors: Philipp Erni, Peter Fischer, Erich J. WindhabAbstract:The shear and dilatational rheology of condensed interfacial layers of the water-insoluble surfactant Sorbitan Tristearate at the air/water interface is investigated. A new interfacial shear rheometer allows measurements in both stress- and strain-controlled modes, providing comprehensive interfacial rheological information such as the interfacial dynamic shear moduli, the creep response to a stress pulse, the stress relaxation response to a strain step, or steady shear curves. Our experiments show that the interfacial films are both viscoelastic and brittle in nature and subject to fracture at small deformations, as was supported by in-situ Brewster angle microscopy performed during the rheological experiments. Although any large-deformation test is destructive to the sample, it is still possible to study the linear viscoelastic regime if the deformations involved are controlled carefully. Complementary results for the dilatational rheology in area step compression/expansion experiments are reported. The dilatational behavior is predominantly elastic throughout the frequency spectrum measured, whereas the layers exhibit generalized Maxwell behavior in shear mode within a deformation frequency regime as narrow as two decades, indicating the presence of additional relaxation mechanisms in shear as opposed to expansion/compression. If the transient rheological response from stress relaxation experiments is considered, then the data can be described well with a stretched exponential model both in the shear and dilatational deformations.
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Sorbitan Tristearate layers at the air water interface studied by shear and dilatational interfacial rheology
Langmuir, 2005Co-Authors: Philipp Erni, Peter Fischer, Erich J. WindhabAbstract:The shear and dilatational rheology of condensed interfacial layers of the water-insoluble surfactant Sorbitan Tristearate at the air/water interface is investigated. A new interfacial shear rheometer allows measurements in both stress- and strain-controlled modes, providing comprehensive interfacial rheological information such as the interfacial dynamic shear moduli, the creep response to a stress pulse, the stress relaxation response to a strain step, or steady shear curves. Our experiments show that the interfacial films are both viscoelastic and brittle in nature and subject to fracture at small deformations, as was supported by in-situ Brewster angle microscopy performed during the rheological experiments. Although any large-deformation test is destructive to the sample, it is still possible to study the linear viscoelastic regime if the deformations involved are controlled carefully. Complementary results for the dilatational rheology in area step compression/expansion experiments are reported. The dilatational behavior is predominantly elastic throughout the frequency spectrum measured, whereas the layers exhibit generalized Maxwell behavior in shear mode within a deformation frequency regime as narrow as two decades, indicating the presence of additional relaxation mechanisms in shear as opposed to expansion/compression. If the transient rheological response from stress relaxation experiments is considered, then the data can be described well with a stretched exponential model both in the shear and dilatational deformations.
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Rheology of gas/liquid and liquid/liquid interfaces with aqueous and biopolymer subphases
Mesophases Polymers and Particles, 2004Co-Authors: Philipp Erni, Peter Fischer, Erich J. Windhab, Victor Kusnezov, Patrick Heyer, Jorg LaugerAbstract:The stability, performance and quality of multiphase fluid products such as emulsions or foams are strongly influenced by the structure and rheology of the interfacial film between two immiscible liquids or between air and a liquid. In this study, an interfacial shear rheometer for both stress- and strain-controlled measurements at liquid/liquid and gas/liquid interfaces is used to study the interfacial rheology of the water-insoluble surfactant Sorbitan Tristearate. The subphase is either pure water or an aqueous viscous solution of κ-carrageenan. Air/water and air/solution as well as oil/solution interfaces with different bulk viscosity ratios are investigated. Experiments were performed in steady and oscillatory shear, as well as in stress relaxation (strain step) and creep recovery (stress pulse) mode. A setup combining interfacial rheometry with Brewster-angle microscopy (BAM) is presented and used for real-time imaging of the gas/liquid interface during rheological experiments. The problem of fracture in interfacial films during shear flow even at small deformations is addressed using both interfacial rheometry and BAM images.
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Interfacial Rheology of Gas/Liquid and Liquid/Liquid Interfaces
2004Co-Authors: Philipp Erni, Peter Fischer, Erich J. WindhabAbstract:An interfacial shear rheometer for stressand strain-controlled measurements at liquid interfaces is outlined. Experimental data are reported for the surfactant Sorbitan Tristearate on κ-carrageenan subphases. A setup combining interfacial rheometry with Brewster-angle Microscopy for realtime imaging of the interface is presented.
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stress and strain controlled measurements of interfacial shear viscosity and viscoelasticity at liquid liquid and gas liquid interfaces
Review of Scientific Instruments, 2003Co-Authors: Philipp Erni, Peter Fischer, Erich J. Windhab, Victor Kusnezov, Heiko Stettin, Jorg LaugerAbstract:An interfacial rheometer for both stress- and strain-controlled measurements of shear rheological properties at liquid/liquid and gas/liquid interfaces is presented. The device is based on a rotating or oscillating biconical bob design in combination with a low friction electronically commutated motor system. The interfacial shear stress, viscosity, and dynamic moduli are obtained by solving the Stokes equations (low Reynolds number) along with the Boussinesq–Scriven interfacial stress tensor, which is used for the boundary conditions at the interface. An improved and simple numerical method for the calculation of the velocity distribution in the measuring cell is presented. The scope and limitations of the rheometer are discussed. Results from steady shear and oscillatory experiments as well as creep recovery and stress relaxation tests at both oil/water and air/water interfaces with adsorbed films of a globular protein (ovalbumin) and spread films of a surfactant (Sorbitan Tristearate) are presented.