The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Vivek Sharma - One of the best experts on this subject based on the ideXlab platform.
-
the rheology of aqueous solutions of ethyl hydroxy ethyl cellulose ehec and its hydrophobically modified analogue hmehec extensional flow response in capillary break up jetting rojer and in a cross slot extensional rheometer
Soft Matter, 2015Co-Authors: Vivek Sharma, Simon J Haward, James G Serdy, Bavand Keshavarz, Asa Soderlund, Phil Threlfallholmes, Gareth H MckinleyAbstract:Cellulose derivatives containing associating hydrophobic groups along their hydrophilic backbone are used as rheology modifiers in the formulation of water-based spray paints, medicinal sprays, cosmetics and printable inks. Jetting and spraying applications of these materials involve progressive thinning and break-up of a Fluid Column or sheet into drops. Strong extensional kinematics develop in the thinning Fluid neck. In viscous Newtonian Fluids, inertial and viscous stresses oppose the surface tension-driven instability. In aqueous solutions of polymers such as Ethyl Hydroxy-Ethyl Cellulose (EHEC), chain elongation provides additional elastic stresses that can delay the capillary-driven pinch-off, influencing the sprayability or jettability of the complex Fluid. In this study, we quantify the transient response of thinning filaments of cellulose ether solutions to extensional flows in a Capillary Break-up Extensional Rheometer (CaBER) and in a forced jet undergoing break-up using Rayleigh Ohnesorge Jetting Extensional Rheometry (ROJER). We also characterize the steady state molecular deformations using measurements of the flow-induced birefringence and excess pressure drop in an extensional stagnation point flow using a Cross-Slot Extensional Rheometer (CSER). We show that under the high extension rates encountered in jetting and spraying, the semi-dilute solutions of hydrophobically modified ethyl hydroxy-ethyl cellulose (hmEHEC) exhibit extensional thinning, while the unmodified bare chains of EHEC display an increase in extensional viscosity, up to a plateau value. For both EHEC and hmEHEC dispersions, the low extensibility of the cellulose derivatives limits the Trouton ratio observed at the highest extension rates attained (close to 105 s−1) to around 10–20. The reduction in extensional viscosity with increasing extension rate for the hydrophobically modified cellulose ether is primarily caused by the disruption of a transient elastic network that is initially formed by intermolecular association of hydrophobic stickers. This extensional thinning behavior, in conjunction with the low extensibility of the hydrophobically modified cellulose ether additives, makes these rheology modifiers ideal for controlling the extensional rheology in formulations that require jetting or spraying, with minimal residual stringiness or stranding.
Simon J Haward - One of the best experts on this subject based on the ideXlab platform.
-
the rheology of aqueous solutions of ethyl hydroxy ethyl cellulose ehec and its hydrophobically modified analogue hmehec extensional flow response in capillary break up jetting rojer and in a cross slot extensional rheometer
Soft Matter, 2015Co-Authors: Vivek Sharma, Simon J Haward, James G Serdy, Bavand Keshavarz, Asa Soderlund, Phil Threlfallholmes, Gareth H MckinleyAbstract:Cellulose derivatives containing associating hydrophobic groups along their hydrophilic backbone are used as rheology modifiers in the formulation of water-based spray paints, medicinal sprays, cosmetics and printable inks. Jetting and spraying applications of these materials involve progressive thinning and break-up of a Fluid Column or sheet into drops. Strong extensional kinematics develop in the thinning Fluid neck. In viscous Newtonian Fluids, inertial and viscous stresses oppose the surface tension-driven instability. In aqueous solutions of polymers such as Ethyl Hydroxy-Ethyl Cellulose (EHEC), chain elongation provides additional elastic stresses that can delay the capillary-driven pinch-off, influencing the sprayability or jettability of the complex Fluid. In this study, we quantify the transient response of thinning filaments of cellulose ether solutions to extensional flows in a Capillary Break-up Extensional Rheometer (CaBER) and in a forced jet undergoing break-up using Rayleigh Ohnesorge Jetting Extensional Rheometry (ROJER). We also characterize the steady state molecular deformations using measurements of the flow-induced birefringence and excess pressure drop in an extensional stagnation point flow using a Cross-Slot Extensional Rheometer (CSER). We show that under the high extension rates encountered in jetting and spraying, the semi-dilute solutions of hydrophobically modified ethyl hydroxy-ethyl cellulose (hmEHEC) exhibit extensional thinning, while the unmodified bare chains of EHEC display an increase in extensional viscosity, up to a plateau value. For both EHEC and hmEHEC dispersions, the low extensibility of the cellulose derivatives limits the Trouton ratio observed at the highest extension rates attained (close to 105 s−1) to around 10–20. The reduction in extensional viscosity with increasing extension rate for the hydrophobically modified cellulose ether is primarily caused by the disruption of a transient elastic network that is initially formed by intermolecular association of hydrophobic stickers. This extensional thinning behavior, in conjunction with the low extensibility of the hydrophobically modified cellulose ether additives, makes these rheology modifiers ideal for controlling the extensional rheology in formulations that require jetting or spraying, with minimal residual stringiness or stranding.
Gareth H Mckinley - One of the best experts on this subject based on the ideXlab platform.
-
the rheology of aqueous solutions of ethyl hydroxy ethyl cellulose ehec and its hydrophobically modified analogue hmehec extensional flow response in capillary break up jetting rojer and in a cross slot extensional rheometer
Soft Matter, 2015Co-Authors: Vivek Sharma, Simon J Haward, James G Serdy, Bavand Keshavarz, Asa Soderlund, Phil Threlfallholmes, Gareth H MckinleyAbstract:Cellulose derivatives containing associating hydrophobic groups along their hydrophilic backbone are used as rheology modifiers in the formulation of water-based spray paints, medicinal sprays, cosmetics and printable inks. Jetting and spraying applications of these materials involve progressive thinning and break-up of a Fluid Column or sheet into drops. Strong extensional kinematics develop in the thinning Fluid neck. In viscous Newtonian Fluids, inertial and viscous stresses oppose the surface tension-driven instability. In aqueous solutions of polymers such as Ethyl Hydroxy-Ethyl Cellulose (EHEC), chain elongation provides additional elastic stresses that can delay the capillary-driven pinch-off, influencing the sprayability or jettability of the complex Fluid. In this study, we quantify the transient response of thinning filaments of cellulose ether solutions to extensional flows in a Capillary Break-up Extensional Rheometer (CaBER) and in a forced jet undergoing break-up using Rayleigh Ohnesorge Jetting Extensional Rheometry (ROJER). We also characterize the steady state molecular deformations using measurements of the flow-induced birefringence and excess pressure drop in an extensional stagnation point flow using a Cross-Slot Extensional Rheometer (CSER). We show that under the high extension rates encountered in jetting and spraying, the semi-dilute solutions of hydrophobically modified ethyl hydroxy-ethyl cellulose (hmEHEC) exhibit extensional thinning, while the unmodified bare chains of EHEC display an increase in extensional viscosity, up to a plateau value. For both EHEC and hmEHEC dispersions, the low extensibility of the cellulose derivatives limits the Trouton ratio observed at the highest extension rates attained (close to 105 s−1) to around 10–20. The reduction in extensional viscosity with increasing extension rate for the hydrophobically modified cellulose ether is primarily caused by the disruption of a transient elastic network that is initially formed by intermolecular association of hydrophobic stickers. This extensional thinning behavior, in conjunction with the low extensibility of the hydrophobically modified cellulose ether additives, makes these rheology modifiers ideal for controlling the extensional rheology in formulations that require jetting or spraying, with minimal residual stringiness or stranding.
-
stress relaxation and elastic decohesion of viscoelastic polymer solutions in extensional flow
Journal of Non-newtonian Fluid Mechanics, 1996Co-Authors: Stephen H Spiegelberg, Gareth H MckinleyAbstract:Abstract The evolution of the transient extensional stresses in dilute and semi-dilute viscoelastic polymer solutions was measured with a filament stretching rheometer of a design similar to that first introduced by Sridhar et al. The solutions were polystyrene-based Boger Fluids which were stretched at constant strain rates in the range 0.6 ⩽ ϵ 0 ⩽ 4 s−1 and to Hencky strains of ϵ > 4. The test Fluids all strain-hardened and Trouton ratios exceeding 1000 were obtained at high strains. In addition to measuring the transient tensile stress growth, the decay of the tensile viscoelastic stress in the Fluid Column following cessation of uniaxial elongation was also monitored as a function of the total imposed Hencky strain and the strain rate. The measured relaxation functions were found to be significantly different from those observed following cessation of steady shear flow. The extensional stresses initially decayed very rapidly upon cessation of uniaxial elongation followed by a slower viscoelastic relaxation. For the most elastic Fluids, partial decohesion of the Fluid filament from the endplates of the rheometer was observed in tests conducted at high strain rates. This elastic instability is initiated near the rigid endplate fixtures of the device and it results in the progressive breakup of the Fluid Column into individual threads or ‘fibrils’ with a regular azimuthal spacing. These fibrils elongate and bifurcate as the Fluid sample is elongated further. In tests conducted at the highest Deborah numbers, complete sample decohesion from the endplates and rapid elastic recoil were sometimes observed. The critical stress and strain at the onset of the instability were determined by monitoring the tensile force exerted by the filament, the sample radius, and were used to construct an approximate stability diagram. Flow visualization experiments using a modified stretching device showed that the instability develops as a consequence of an axisymmetry-breaking meniscus instability in the non-homogeneous region of highly deformed Fluid near the rigid endplate.
-
the role of end effects on measurements of extensional viscosity in filament stretching rheometers
Journal of Non-newtonian Fluid Mechanics, 1996Co-Authors: Stephen H Spiegelberg, David C Ables, Gareth H MckinleyAbstract:Abstract The transient extensional viscosity function of two semi-dilute polyisobutylene polymer solutions is investigated in a filament stretching rheometer of the type developed by Tirtaatmadja and Sridhar (J. Rheol., 37 (1993) 1081). A velocity compensation algorithm which yields a constant deformation rate at a single point in both Newtonian and non-Newtonian Fluid samples is detailed. Good experimental reproducibility is obtained in the device and measurements with a viscous Newtonian oil yield steady-state Trouton ratios of η μ = 3 ± 0.5 . Both viscoelastic Fluids show the onset of significant strain-hardening for Hencky strains greater than two, and transient extensional viscosities that increase by three orders of magnitude. Good agreement between the results for the two different Fluids is obtained when tests are performed at identical values of the Deborah number. The maximum Hencky strain achievable in the device is ϵ = 5 and steady-state values of the extensional viscosity are never achieved over the range of strain rates attainable. Measurements show that the evolution of the tensile force exerted by the deforming filament is a strong function of the initial aspect ratio of the cylindrical test sample. A lubrication analysis for small sample aspect ratios demonstrates that this variation results from large radial pressure gradients arising from the non-homogeneous shear flow near the rigid disks. This simplified analysis provides a good description of the experimental observations, and tests conducted with the Newtonian oil suggest that only at Hencky strains ϵ > 2 does the extensional deformation of the filament dominate the shearing flow. In the case of viscoelastic Fluid filaments, the initial shearing motion near the fixed endplates significantly affects the measured tensile stress in the filament at all later times in the extension. Careful attention is focused on the non-homogeneous deformation induced at the endplates that constrain the Fluid sample at each end of the test apparatus. Measurements of the filament profile and surface curvature with a video-imaging system show distinct differences in the evolution of Newtonian and non-Newtonian samples. In both cases, different strain histories are experienced by Fluid elements at different axial positions in the filament, and a spatially homogenous deformation is not achieved in the viscoelastic filaments until Hencky strains ϵ > 4 are attained. Observations at larger strains and high Deborah numbers, De > 3, indicate the onset of an elastic instability near the stationary endplate which results in the deforming Fluid Column partially decohering from the endplate.
Norman M Wereley - One of the best experts on this subject based on the ideXlab platform.
-
Vertical Axis Inductance Monitoring System to Measure Stratification in a Column of Magnetorheological Fluid
IEEE Transactions on Magnetics, 2017Co-Authors: Jonathan M. Chambers, Norman M WereleyAbstract:This paper addresses an automated method and experimental apparatus to measure the sedimentation of magnetorheological Fluids (MRFs) in a vertical Column. The automated vertical axis inductance system (AVAIMS) developed at the University of Maryland monitored the particle concentration (i.e., particle volume fraction) of an MRF as a function of Column height and standing time through an automatic process of scanning with an inductance sensor driven by a stepper motor. With the acquired data, the extent and the concentration gradients of four distinct sedimentation zones were monitored and automatically determined without human decision-based post-processing of data: supernatant zone, original concentration zone, variable concentration zone, and sediment zone. The evolution of these sedimentation zones provides a characterization of an MRF's sedimentation behavior. Insights gained from these studies enable a better understanding of the dynamics of hindered settling of MRFs in closed systems, such as in rotary or linear stroke magnetorheological energy absorbers. An MRF sample consisting of carbonyl iron powder in a silicone carrier Fluid with an initially uniform 21% particle volume fraction (hereinafter 21 vol%) was synthesized to demonstrate the method and the automated analysis of the AVAIMS. The 130 mm Fluid Column was scanned from top to bottom in 0.5 mm increments every 3 h for a total sedimentation period of six days (144 h). The results proved to be comparable to the characterizations obtained from our previous study with a manually operated VAIMS.
-
measuring the sedimentation rate in a magnetorheological Fluid Column via thermal conductivity monitoring
Smart Materials and Structures, 2016Co-Authors: Haibin Cheng, Xiaopeng Zhang, Guizhen Liu, Norman M WereleyAbstract:Measuring sedimentation rate of magnetorheological Fluids (MRFs) is of great importance when designing and synthesizing MRFs for engineering applications. A method of characterizing sedimentation rate in an MRF Column is proposed utilizing thermal conductivity correlated with particle concentration. A series of MRF samples composed of carbonyl iron particles suspended in silicone oil were prepared, and their concentrations (measured as volume fraction, ∅) and thermal conductivities, k, were tested. A calibration curve was developed to relate particle concentration, ∅, to thermal conductivity, k, using this set of MRF samples with known concentration. The particle concentration, ∅, in the MRF Column was then monitored by measuring thermal conductivities (k) at a fixed location and using this calibration relationship. Finally, sedimentation rate in the MRF Column was determined by examining how particle concentration varied with time. The sedimentation rate measured in the MRF Column was validated using visual observation of mudline (boundary between the topmost clarified Fluid zone and MRF below).
-
testing and analysis of magnetorheological Fluid sedimentation in a Column using a vertical axis inductance monitoring system
Smart Materials and Structures, 2016Co-Authors: Youngtai Choi, Lei Xie, Norman M WereleyAbstract:This study investigates the sedimentation of magnetorheological Fluids (MRFs) in a vertical Column using a vertical axis inductance monitoring system (VAIMS). The particle concentration (i.e., particle volume fraction) of MRF samples consisting of carbonyl iron powder in a silicone carrier Fluid was monitored as a function of Column height for 156 h with a measurement nominally every 12 h. In addition, the extent and concentration gradients in four distinct sedimentation zones were monitored: supernatant zone, original concentration zone, variable concentration zone, and sediment zone. In order to obtain the settling velocity of the MRF with respect to particle concentration, MRF samples with different volume fractions (i.e., 15, 19, 26, 30 and 40 vol%) were synthesized, and mudline (i.e., the boundary between clarified supernatant Fluid zone and the original concentration zone below) descent of each sample was measured using both the VAIMS and visual observation. In this study, three different settling velocity models (i.e., Vesilind, Richardson and Zaki, and Dick models) were considered in order to capture settling velocity as a function of concentration. Vesilind's settling velocity model was found to be most suitable for the MRF sample in our study, and the setting velocity distribution in the vertical Column could be measured for each MRF sample. Based on Kynch's sedimentation analysis, the mass balance equation was obtained and integrated with Vesilind's settling velocity model to obtain the concentration propagation velocity. In addition, the solids flux within the Fluid Column was obtained to provide insight in sedimentation stability as a function of particle concentration.
Phil Threlfallholmes - One of the best experts on this subject based on the ideXlab platform.
-
the rheology of aqueous solutions of ethyl hydroxy ethyl cellulose ehec and its hydrophobically modified analogue hmehec extensional flow response in capillary break up jetting rojer and in a cross slot extensional rheometer
Soft Matter, 2015Co-Authors: Vivek Sharma, Simon J Haward, James G Serdy, Bavand Keshavarz, Asa Soderlund, Phil Threlfallholmes, Gareth H MckinleyAbstract:Cellulose derivatives containing associating hydrophobic groups along their hydrophilic backbone are used as rheology modifiers in the formulation of water-based spray paints, medicinal sprays, cosmetics and printable inks. Jetting and spraying applications of these materials involve progressive thinning and break-up of a Fluid Column or sheet into drops. Strong extensional kinematics develop in the thinning Fluid neck. In viscous Newtonian Fluids, inertial and viscous stresses oppose the surface tension-driven instability. In aqueous solutions of polymers such as Ethyl Hydroxy-Ethyl Cellulose (EHEC), chain elongation provides additional elastic stresses that can delay the capillary-driven pinch-off, influencing the sprayability or jettability of the complex Fluid. In this study, we quantify the transient response of thinning filaments of cellulose ether solutions to extensional flows in a Capillary Break-up Extensional Rheometer (CaBER) and in a forced jet undergoing break-up using Rayleigh Ohnesorge Jetting Extensional Rheometry (ROJER). We also characterize the steady state molecular deformations using measurements of the flow-induced birefringence and excess pressure drop in an extensional stagnation point flow using a Cross-Slot Extensional Rheometer (CSER). We show that under the high extension rates encountered in jetting and spraying, the semi-dilute solutions of hydrophobically modified ethyl hydroxy-ethyl cellulose (hmEHEC) exhibit extensional thinning, while the unmodified bare chains of EHEC display an increase in extensional viscosity, up to a plateau value. For both EHEC and hmEHEC dispersions, the low extensibility of the cellulose derivatives limits the Trouton ratio observed at the highest extension rates attained (close to 105 s−1) to around 10–20. The reduction in extensional viscosity with increasing extension rate for the hydrophobically modified cellulose ether is primarily caused by the disruption of a transient elastic network that is initially formed by intermolecular association of hydrophobic stickers. This extensional thinning behavior, in conjunction with the low extensibility of the hydrophobically modified cellulose ether additives, makes these rheology modifiers ideal for controlling the extensional rheology in formulations that require jetting or spraying, with minimal residual stringiness or stranding.