Shear Thickening in Dilute Polymer Solutions: Transient Analysis

Kamerkar, P. A.; Edwards, Brian J.; Keffer, David J.; Reneau, C. W.

doi:10.1080/00986440590473263

Cited by 7 publications

(4 citation statements)

References 15 publications

(35 reference statements)

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“…PFCB/chloroform and PFCB/THF solutions exhibited slight shear thickening over the measured shear rate range (data given in Supporting Information). Shear thickening behavior of dilute polymer solutions is known to occur for dilute solutions of polymers with molecular weight higher than 1 × 10 5 Da in low viscosity Newtonian fluids at moderate shear rates (100 to 3000 s −1 ) 18–20. Shear thickening may be explained by entanglement of polymer chains resulting from shear, turbulence, and Brownian motion 21.…”

Section: Resultsmentioning

confidence: 99%

Formation and characterization of perfluorocyclobutyl polymer thin films

Zhou

Jin

Haldeman

et al. 2013

J of Applied Polymer Sci

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Perfluorocyclobutyl (PFCB) polymers are a new class of materials that show promise as selective layer materials in the development of composite membranes for gas separations, such as carbon dioxide/methane (a pure gas ¼ 38.6) and oxygen/nitrogen (a pure gas ¼ 4.8) separations. In many of the flat sheet applications, a thin film of the selective layer that is free of major defects must be coated onto a support membrane. A focus of this study was to elucidate the impacts of solvents, polymer concentration, and dipcoating withdrawal speed on PFCB thin film thickness and uniformity. An extension was proposed to the Landau-Levich model to estimate the polymer film thickness. The results show that the extended model fits the thickness-withdrawal speed data well above about 55 mm/min, but, at lower withdrawal speeds, the data deviated from the model. This deviation could be explained by the phenomenon of polymer surface excess. Static surface excesses of polymer solutions were estimated by applying the Gibbs adsorption equation using measured surface tension data. Prepared films were characterized by ellipsometry. Refractive index was found to increase with decreasing film thickness below about 50 nm, indicating densification of ultrathin films prepared from PFCB solutions below the overlap concentration. Atomic force microscopy was used to characterize surface morphologies. Films prepared from tetrahydrofuran and chloroform yielded uniform nanolayers. However, films prepared using acetone as solvent yielded a partial dewetting pattern, which could be explained by a surface depletion layer of pure solvent between the bulk PFCB/acetone solution and the substrate.

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Section: Resultsmentioning

confidence: 99%

Formation and characterization of perfluorocyclobutyl polymer thin films

Zhou

Jin

Haldeman

et al. 2013

J of Applied Polymer Sci

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“…1. Further validation of the model may be obtained by examining transient experimental data taken during start up and cessation of shear flow 20…”

Section: Discussionmentioning

confidence: 99%

Modeling shear thickening in dilute polymer solutions: Temperature, concentration, and molecular weight dependencies

Jiang

Keffer

Edwards

et al. 2003

J of Applied Polymer Sci

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The Two Coupled Maxwell Modes (TCMM)Model is applied to give quantitative descriptions of shearthickening behavior, which can be observed under certain conditions for high molecular weight polymers dissolved in low viscosity solvents. The TCMM Model is written in terms of five parameters representing the relaxation time of each mode, the concentration of each mode, and a coupling parameter between the two modes. Using all of the available experimental data for steady-shear viscosity and dichroism we found in the literature, we performed a full parameterization of these five quantities. Furthermore, from this parameterization we can describe the functional dependencies of the relaxation times, modal concentrations, and coupling parameter as functions of temperature, concentration, and molecular weight of the polymer. These functional dependencies are explained in light of the underlying physics imbedded in the TCMM Model. We demonstrate that by optimizing to only the viscosity data, we were able to obtain the same relaxation times, modal concentrations, and coupling parameter as using both the viscosity and dichroism data. This is useful because typically the experimental dichroism data is not available.

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“…However, development of high-fidelity models to describe the rapid unravelling of entangled macromolecules in strong flows has been a longstanding challenge for the rheology and the polymer physics communities. Specifically, the intense molecular deformations realized in this class of flows lead to a host of flow-induced phenomena, including mixing, demixing, phase transitions, crystallization, − concentration fluctuations and inhomogeneities, − and phase separation. − …”

Section: Introductionmentioning

confidence: 99%

Flow-Induced Phase Separation and Crystallization in Entangled Polyethylene Solutions under Elongational Flow

2020

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Flow-induced phenomena in entangled solutions of linear C1000H2002 polyethylene dissolved in n-hexadecane and benzene solvents were simulated via nonequilibrium molecular dynamics at concentrations of 14.5C* and 13.5C*, respectively, of the coil overlap concentration, C*. The simulations revealed that both solutions undergo a chemical phase separation when subject to planar extensional flow at extension rates faster than the inverse Rouse time of the solution. The onset of phase separation initiated after roughly two Hencky strain units of deformation for both solutions and attained a stationary state at about ten Hencky strain units. Furthermore, the simulations revealed that at very high extension rates the polymer phase forms semicrystalline domains regardless of the solvent; however, the critical extension rate for flow-induced crystallization appeared to be affected by a number of variables, including solution temperature and the chemical nature of the solvent.

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Shear Thickening in Dilute Polymer Solutions: Transient Analysis

Cited by 7 publications

References 15 publications

Formation and characterization of perfluorocyclobutyl polymer thin films

Formation and characterization of perfluorocyclobutyl polymer thin films

Modeling shear thickening in dilute polymer solutions: Temperature, concentration, and molecular weight dependencies

Flow-Induced Phase Separation and Crystallization in Entangled Polyethylene Solutions under Elongational Flow

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