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Articles 451 - 458 of 458

Full-Text Articles in Materials Science and Engineering

Extreme Strain Localization And Sliding Friction In Physically Associating Polymer Gels, Kendra Erk, Jeffrey D. Martin, Y. Thomas Hu, Kenneth R. Shull Jan 2012

Extreme Strain Localization And Sliding Friction In Physically Associating Polymer Gels, Kendra Erk, Jeffrey D. Martin, Y. Thomas Hu, Kenneth R. Shull

School of Materials Engineering Faculty Publications

Model physically associating gels deformed in shear over a wide range of reduced rates displayed evidence of strain localization. The non-linear stress responses and inhomogeneous velocity profiles observed during shear rheometry coupled with particle tracking velocimetry were associated with the occurrence of rate-dependent, banding and fracture-like responses in the gel. Scaling law analysis from traditional sliding friction studies suggests that at the molecular level, deformation is confined to a shear zone with thickness comparable to the gel’s mesh size, the smallest structurally relevant length scale in the gel.

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Shear And Dilational Interfacial Rheology Of Surfactant-Stabilized Droplets, Kendra Erk, Jeffrey D. Martin, Jonathan T. Schwalbe, Frederick R. Phelan Jr., Steven D. Hudson Jan 2012

Shear And Dilational Interfacial Rheology Of Surfactant-Stabilized Droplets, Kendra Erk, Jeffrey D. Martin, Jonathan T. Schwalbe, Frederick R. Phelan Jr., Steven D. Hudson

School of Materials Engineering Faculty Publications

A new measurement method is suggested that is capable of probing the shear and dilational interfacial rheological responses of small droplets, those of size comparable to real emulsion applications. Freely suspended aqueous droplets containing surfactant and non-surface-active tracer particles are transported through a rectangular microchannel by the plane Poiseuille flow of the continuous oil phase. Optical microscopy and high-speed imaging record the shape and internal circulation dynamics of the droplets. Measured circulation velocities are coupled with theoretical descriptions of the droplet dynamics in order to determine the viscous (Boussinesq) and elastic (Marangoni) interfacial effects. A new Marangoni-induced stagnation point is …

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Interfacial Effects On Droplet Dynamics In Poiseuille Flow, Kendra Erk, Jonathan T. Schwalbe, Frederick R. Phelan Jr., Petia M. Vlahovska, Steven D. Hudson Mar 2011

Interfacial Effects On Droplet Dynamics In Poiseuille Flow, Kendra Erk, Jonathan T. Schwalbe, Frederick R. Phelan Jr., Petia M. Vlahovska, Steven D. Hudson

School of Materials Engineering Faculty Publications

Many properties of emulsions arise from interfacial rheology, but a theoretical understanding of the effect of interfacial viscosities on droplet dynamics is lacking. Here we report such a theory, relating to isolated spherical drops in a Poiseuille flow. Stokes flow is assumed in the bulk phases, and a jump in hydrodynamic stress at the interface is balanced by Marangoni and surface viscous forces according to the Boussinesq–Scriven constitutive law. Our model employs a linear equation of state for the surfactant. Our analysis predicts slip, cross-stream migration and droplet-circulation velocities. These results and the corresponding interfacial parameters are separable: e.g., cross-stream …

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Rate-Dependent Stiffening And Strain Localization In Physically Associating Solutions, Kendra Erk, Kenneth R. Shull Jan 2011

Rate-Dependent Stiffening And Strain Localization In Physically Associating Solutions, Kendra Erk, Kenneth R. Shull

School of Materials Engineering Faculty Publications

Model physically associating solutions of acrylic triblock copolymer molecules in a midblock-selective solvent displayed non-linear strain-stiffening behavior which transitioned to rapid strain softening during shear start-up experiments at reduced rates spanning almost four orders of magnitude. Softening was believed to result from the shear-induced formation of highly localized regions of deformation in the macromolecular network. This behavior was accurately captured by a model that incorporated the strain energy and relaxation behavior of individual network strands in the solution. Flow curves predicted from the model were non-monotonic, consistent with the onset of flow instabilities at high shear rates. The non-linear stress …

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Strain-Stiffening In Synthetic And Biopolymer Networks, Kendra Erk, Kevin J. Henderson, Kenneth R. Shull Jan 2010

Strain-Stiffening In Synthetic And Biopolymer Networks, Kendra Erk, Kevin J. Henderson, Kenneth R. Shull

School of Materials Engineering Faculty Publications

Strain-stiffening behavior common to biopolymer networks is difficult to reproduce in synthetic networks. Physically associating synthetic polymer networks can be an exception to this rule and can demonstrate strain-stiffening behavior at relatively low values of strain. Here, the stiffening behavior of model elastic networks of physically associating triblock copolymers is characterized by shear rheometry. Experiments demonstrate a clear correlation between network structure and strain-stiffening behavior. Stiffening is accurately captured by a constitutive model with a single fitting parameter related to the midblock length. The same model is also effective for describing the stiffening of actin, collagen, and other biopolymer networks. …

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Strain Energy And Lateral Friction Force Distributions Of Carbon Nanotubes Manipulated Into Shapes By Atomic Force Microscopy, Mark C. Strus, Roya R. Lahiji, Pablo Ares, Vincente Lopez, Arvind Raman, Ron R. Reifenberger Aug 2009

Strain Energy And Lateral Friction Force Distributions Of Carbon Nanotubes Manipulated Into Shapes By Atomic Force Microscopy, Mark C. Strus, Roya R. Lahiji, Pablo Ares, Vincente Lopez, Arvind Raman, Ron R. Reifenberger

Other Nanotechnology Publications

The interplay between local mechanical strain energy and lateral frictional forces determines the shape of carbon nanotubes on substrates. In turn, because of its nanometer-size diameter, the shape of a carbon nanotube strongly influences its local electronic, chemical, and mechanical properties. Few, if any, methods exist for resolving the strain energy and static frictional forces along the length of a deformed nanotube supported on a substrate. We present a method using nonlinear elastic rod theory in which we compute the flexural strain energy and static frictional forces along the length of single walled carbon nanotubes (SWCNTs) manipulated into various shapes …

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Interfacial Energy Between Carbon Nanotubes And Polymers Measured From Nanoscale Peel Tests In The Atomic Force Microscope, Mark C. Strus, Camilo I. Cano, R. Byron Pipes, Cattien V. Nguyen, Arvind Raman Mar 2009

Interfacial Energy Between Carbon Nanotubes And Polymers Measured From Nanoscale Peel Tests In The Atomic Force Microscope, Mark C. Strus, Camilo I. Cano, R. Byron Pipes, Cattien V. Nguyen, Arvind Raman

Other Nanotechnology Publications

The future development of polymer composite materials with nanotubes or nanoscale fibers requires the ability to understand and improve the interfacial bonding at the nanotube-polymer matrix interface. In recent work [Strus MC, Zalamea L, Raman A, Pipes RB, Nguyen CV, Stach EA. Peeling force spectroscopy: exposing the adhesive nanomechanics of one-dimensional nanostructures. Nano Lett 2008;8(2):544–50], it has been shown that a new mode in the Atomic Force Microscope (AFM), peeling force spectroscopy, can be used to understand the adhesive mechanics of carbon nanotubes peeled from a surface. In the present work, we demonstrate how AFM peeling force spectroscopy can be …

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The Effect Of Texture And Microstructure On Equibiaxial Fracture In Gallium Embrittled Aluminum Sheet, Michael Daniel Grah Oct 1993

The Effect Of Texture And Microstructure On Equibiaxial Fracture In Gallium Embrittled Aluminum Sheet, Michael Daniel Grah

Open Access Dissertations

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