Browsing by Author "Rogers, Simon A."
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Item Dynamic shear rheology of a thixotropic suspension: Comparison of an improved structure-based model with large amplitude oscillatory shear experiments(The Society of Rheology, 2016-03-29) Armstrong, Matthew J.; Beris, Antony N.; Rogers, Simon A.; Wagner, Norman J.; Matthew J. Armstrong, Antony N. Beris, Simon A. Rogers, and Norman J. Wagner; Armstrong, Matthew J.; Beris, Antony N.; Rogers, Simon A.; Wagner, Norman J.Rheological measurements on a model thixotropic suspension by Dullaert and Mewis [J. Non-Newtonian Fluid Mech. 139(1–2), 21–30 (2006); Rheol. Acta 45, 23–32 (2005)] are extended to include large amplitude oscillatory shear (LAOS) flow, shear flow reversal, and a novel unidirectional LAOS flow to provide an extended rheological data set for testing constitutive models. We use this extended data set to test a new structure-based model developed by improving the Delaware thixotropic model [A. Mujumdar et al., J. Non-Newtonian Fluid Mech. 102, 157–178 (2002); A. J. Apostolidis et al., J. Rheol. 59, 275–298 (2015)]. Model parameters are determined from steady, small amplitude oscillatory, and step shear rate tests. Holding those parameters fixed, model predictions are compared to LAOS experiments. Similar comparisons are made for three contemporary models from the literature. Two of these models use a scalar internal structural parameter and include the modified Jeffreys model proposed by de Souza Mendes and Thompson [Rheol. Acta 52, 673–694 (2013)]. The third model is based on fluidity additivity [F. Bautista et al., J. Non-Newtonian Fluid Mech. 80, 93–113 (1999)]. A common weakness in all models is shown to be the use of scalar order parameters that cannot account for the reversal of flow directionality inherent in LAOS flow. This is further illustrated by comparison with flow reversal and unidirectional LAOS experiments.Item Dynamic shear rheology of a thixotropic suspension: Comparison of an improved structure-based model with large amplitude oscillatory shear experiments(The Society of Rheology, 2016-03-29) Armstrong, Matthew J.; Beris, Antony N.; Rogers, Simon A.; Wagner, Norman J.; Matthew J. Armstrong, Antony N. Beris, Simon A. Rogers, and Norman J. Wagner; Armstrong, Matthew J.; Beris, Antony N; Rogers, Simon A.; Wagner, Norman J.Rheological measurements on a model thixotropic suspension by Dullaert and Mewis [J. Non-Newtonian Fluid Mech. 139(1–2), 21–30 (2006); Rheol. Acta 45, 23–32 (2005)] are extended to include large amplitude oscillatory shear (LAOS) flow, shear flow reversal, and a novel unidirectional LAOS flow to provide an extended rheological data set for testing constitutive models. We use this extended data set to test a new structure-based model developed by improving the Delaware thixotropic model [A. Mujumdar et al., J. Non-Newtonian Fluid Mech. 102, 157–178 (2002); A. J. Apostolidis et al., J. Rheol. 59, 275–298 (2015)]. Model parameters are determined from steady, small amplitude oscillatory, and step shear rate tests. Holding those parameters fixed, model predictions are compared to LAOS experiments. Similar comparisons are made for three contemporary models from the literature. Two of these models use a scalar internal structural parameter and include the modified Jeffreys model proposed by de Souza Mendes and Thompson [Rheol. Acta 52, 673–694 (2013)]. The third model is based on fluidity additivity [F. Bautista et al., J. Non-Newtonian Fluid Mech. 80, 93–113 (1999)]. A common weakness in all models is shown to be the use of scalar order parameters that cannot account for the reversal of flow directionality inherent in LAOS flow. This is further illustrated by comparison with flow reversal and unidirectional LAOS experiments.Item An optimized protocol for the analysis of time-resolved elastic scattering experiments(Royal Society of Chemistry, 2016-01-12) Calabrese, Michelle A.; Wagner, Norman J.; Rogers, Simon A.; Michelle A. Calabrese, Norman J. Wagner and Simon A. Rogers; Calabrese, Michelle A.; Wagner, Norman J.; Rogers, Simon A.A deconvolution protocol is developed for obtaining material responses from time-resolved small-angle scattering data from light (SALS), X-rays (SAXS), or neutrons (SANS). Previously used methods convolve material responses with information from the procedure used to group data into discrete time intervals, known as binning. We demonstrate that enhanced signal resolution can be obtained by using methods of signal processing to analyze time-resolved scattering data. The method is illustrated for a timeresolved rheo-SANS measurement of a complex, structured surfactant solution under oscillatory shear flow. We show how the underlying material response can be clearly decoupled from the binning procedure. This method greatly reduces the experimental acquisition time, by approximately one-third for the aforementioned rheo-SANS experiment.Item An optimized protocol for the analysis of time-resolved elastic scattering experiments(Royal Society of Chemistry, 2016-01-12) Calabrese, Michelle A.; Wagner, Norman J.; Rogers, Simon A.; Michelle A. Calabrese, Norman J. Wagner and Simon A. Rogers; Calabrese, Michelle A.; Wagner, Norman J.; Rogers, Simon A.A deconvolution protocol is developed for obtaining material responses from time-resolved small-angle scattering data from light (SALS), X-rays (SAXS), or neutrons (SANS). Previously used methods convolve material responses with information from the procedure used to group data into discrete time intervals, known as binning. We demonstrate that enhanced signal resolution can be obtained by using methods of signal processing to analyze time-resolved scattering data. The method is illustrated for a time-resolved rheo-SANS measurement of a complex, structured surfactant solution under oscillatory shear flow. We show how the underlying material response can be clearly decoupled from the binning procedure. This method greatly reduces the experimental acquisition time, by approximately one-third for the aforementioned rheo-SANS experiment.Item Unlocking Chain Exchange in Highly Amphiphilic Block Polymer Micellar Systems: Influence of Agitation(American Chemical Society, 2014-10-14) Murphy, Ryan P.; Kelley, Elizabeth G.; Rogers, Simon A.; Sullivan, Millicent O.; Epps, Thomas H. III; Ryan P. Murphy, Elizabeth G. Kelley, Simon A. Rogers, Millicent O. Sullivan, and Thomas H. Epps, III; Murphy, Ryan P.; Kelley, Elizabeth G.; Rogers, Simon A.; Sullivan, Millicent O.; Epps, Thomas H. IIIChain exchange between block polymer micelles in highly selective solvents, such as water, is well-known to be arrested under quiescent conditions, yet this work demonstrates that simple agitation methods can induce rapid chain exchange in these solvents. Aqueous solutions containing either pure poly(butadiene-b-ethylene oxide) or pure poly(butadiene-b-ethylene oxide-d4) micelles were combined and then subjected to agitation by vortex mixing, concentric cylinder Couette flow, or nitrogen gas sparging. Subsequently, the extent of chain exchange between micelles was quantified using small angle neutron scattering. Rapid vortex mixing induced chain exchange within minutes, as evidenced by a monotonic decrease in scattered intensity, whereas Couette flow and sparging did not lead to measurable chain exchange over the examined time scale of hours. The linear kinetics with respect to agitation time suggested a surface-limited exchange process at the air–water interface. These findings demonstrate the strong influence of processing conditions on block polymer solution assemblies.