• Title/Summary/Keyword: Rheology Materials

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Non-Newtonian fluid mechanics for polymeric liquids: A status report

  • Leal, L.Gary;Oberhauser, James P.
    • Korea-Australia Rheology Journal
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    • v.12 no.1
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    • pp.1-25
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    • 2000

  • In this paper, we review recent progress in the development of constitutive models for both dilute and entangled polymeric liquids. The status of recent applications of these models for fluid dynamics predictions is then discussed, as well as possible future research directions.

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Modeling of rheological behavior of nanocomposites by Brownian dynamics simulation

  • Song Young Seok;Youn Jae Ryoun
    • Korea-Australia Rheology Journal
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    • v.16 no.4
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    • pp.201-212
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    • 2004

  • Properties of polymer based nanocomposites depend on dispersion state of embedded fillers. In order to examine the effect of dispersion state on rheological properties, a new bi-mode FENE dumbbell model was proposed. The FENE dumbbell model includes two separate ensemble sets of dumbbells with different fric­tion coefficients, which simulate behavior of well dispersed and aggregated carbon nanotubes (CNTs). A new parameter indicating dispersion state of the CNT was proposed to account for degree of dispersion quantitatively as well as qualitatively. Rheological material functions in elongational, steady shear, and oscillatory shear flows were obtained numerically. The CNT/epoxy nanocomposites with different dis­persion state were prepared depending on whether a solvent is used for the dispersion of CNTs or not. Dis­persion state of the CNT in the epoxy nanocomposites was morphologically characterized by the field emission scanning electronic microscope and the transmission electron microscope images. It was found that the numerical prediction was in a good agreement with experimental results especially for steady state shear flow.

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Conformation of single polymer molecule in a slot coating flow

  • Lee, Jeong-Yong;Ryu, Bo-Kyung;Lee, Joo-Sung;Jung, Hyun-Wook;Hyun, Jae-Chun
    • Korea-Australia Rheology Journal
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    • v.20 no.2
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    • pp.89-94
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    • 2008

  • To satisfy good mechanical and optical properties of polymer-coated film products, it will be indispensable to elucidate the molecular orientation of polymer chains within coating liquids in coating flows. Using hybridized numerical method between computational fluid dynamics (CFD) and Brownian dynamics (BD) simulations can provide the useful information for the better quality control of coated films. Flexible polymer chains, e.g., ${\lambda}$-DNA molecules here, change their conformation according to the flow strength and the flow type. The molecular conformation within the coated film on the web or substrate is quite different, because the polymer chains experience the complicated flow strength and flow types in flow field. Especially in the slot coating flow, these chains are more extended by the extension-like flow field generated in the free surface curvature just beyond the downstream die region. Also, the polymer chain extension beneath the free surface can be affected by the die geometry, e.g., the coating gap, changing flow field.

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Hydrogel microrheology near the liquid-solid transition

  • Larsen, Travis;Schultz, Kelly;Furst, Eric M.
    • Korea-Australia Rheology Journal
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    • v.20 no.3
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    • pp.165-173
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    • 2008

  • Multiple particle tracking microrheology is used to characterize the viscoelastic properties of biomaterial and synthetic polymer gels near the liquid-solid transition. Probe particles are dispersed in the gel precursors, and their dynamics are measured as a function of the extent of reaction during gel formation. We interpret the dynamics using the generalized Stokes-Einstein relationship (GSER), using a form of the GSER that emphasizes the relationship between the probe particle mean-squared displacement and the material creep compliance. We show that long-standing concepts in gel bulk rheology are applicable to microrheological data, including time-cure superposition to identify the gel point and critical scaling exponents, and the power-law behavior of incipient network's viscoelastic response. These experiments provide valuable insight into the rheology, structure, and kinetics of gelling materials, and are especially powerful for studying the weak incipient networks of dilute gelators, as well as scarce materials, due to the small sample size requirements and rapid data acquisition.

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