Gregory B. McKenna
- Courses0
- Reviews0
- School: Texas Tech University
- Campus:
- Department: Chemical Engineering
- Email address: Join to see
- Phone: Join to see
-
Location:
2500 Broadway
Lubbock, TX - 79409 - Dates at Texas Tech University: -
- Office Hours: Join to see
Biography
Texas Tech University - Chemical Engineering
Experience
Texas Tech University
Professor
Gregory worked at Texas Tech University as a Professor
National Institute of Standards and Technology (NIST)
Research Scientist/Group Leader
Gregory worked at National Institute of Standards and Technology (NIST) as a Research Scientist/Group Leader
Education
Massachusetts Institute of Technology
MS
University of Utah
Ph.D.
Materials Science and Engineering
United States Air Force Academy
B.S.
Engineering Mechanics
Publications
Mechanical responses of a polymer graphene-sheet nano-sandwich
Polymer
The interfacial mechanics and reinforcement by the graphene sheets in polymer matrix nanocomposites are important to their understanding. However, the methods available for their investigation remain a challenge. Here we report on a novel study in which the mechanical responses of a nano-sandwich model structure made of a single graphene sheet sandwiched between ultrathin polymer layers are determined using a nano-bubble inflation method. The stress-strain behavior of the graphene nano-sandwich shows that significant reinforcement is obtained at small strains and that the method also provides a measurement of the interfacial shear strength. In addition, the study provides data related to internal stresses that develop between the graphene layer and the polymer sandwich faces.
Mechanical responses of a polymer graphene-sheet nano-sandwich
Polymer
The interfacial mechanics and reinforcement by the graphene sheets in polymer matrix nanocomposites are important to their understanding. However, the methods available for their investigation remain a challenge. Here we report on a novel study in which the mechanical responses of a nano-sandwich model structure made of a single graphene sheet sandwiched between ultrathin polymer layers are determined using a nano-bubble inflation method. The stress-strain behavior of the graphene nano-sandwich shows that significant reinforcement is obtained at small strains and that the method also provides a measurement of the interfacial shear strength. In addition, the study provides data related to internal stresses that develop between the graphene layer and the polymer sandwich faces.
Startup shear of a highly entangled polystyrene solution deep into the nonlinear viscoelastic regime
Rheological Acta
Melt flow instability; Edge fracture; Shear banding; Nonlinear rheology; Wall slip; Entangled polymer
Mechanical responses of a polymer graphene-sheet nano-sandwich
Polymer
The interfacial mechanics and reinforcement by the graphene sheets in polymer matrix nanocomposites are important to their understanding. However, the methods available for their investigation remain a challenge. Here we report on a novel study in which the mechanical responses of a nano-sandwich model structure made of a single graphene sheet sandwiched between ultrathin polymer layers are determined using a nano-bubble inflation method. The stress-strain behavior of the graphene nano-sandwich shows that significant reinforcement is obtained at small strains and that the method also provides a measurement of the interfacial shear strength. In addition, the study provides data related to internal stresses that develop between the graphene layer and the polymer sandwich faces.
Startup shear of a highly entangled polystyrene solution deep into the nonlinear viscoelastic regime
Rheological Acta
Melt flow instability; Edge fracture; Shear banding; Nonlinear rheology; Wall slip; Entangled polymer
Forced Assembly by Multilayer Coextrusion to Create Oriented Graphene Reinforced Polymer Nanocomposites
Polymer
A potential advantage of platelet-like nanofillers as nanocomposite reinforcements is the possibility of achieving two-dimensional stiffening through planar orientation of the platelets. The ability to achieve improved properties through in-plane orientation of the platelets is a challenge and, here, we present the first results of using forced assembly to orient graphene nanoplatelets in poly(methyl methacrylate)/polystyrene (PMMA/PS) and PMMA/PMMA multilayer films produced through multilayer coextrusion. The films exhibited a multilayer structure made of alternating layers of polymer and polymer containing graphene as evidenced by electron microscopy. Significant single layer reinforcement of 118 % at a concentration of 2 wt % graphene was achieved—higher than previously reported reinforcement for randomly dispersed graphene. The large reinforcement is attributed to the planar orientation of the graphene in the individual polymer layers. Anisotropy of the stiffening was also observed and attributed to imperfect planar orientation of the graphene lateral to the extrusion flow.
Mechanical responses of a polymer graphene-sheet nano-sandwich
Polymer
The interfacial mechanics and reinforcement by the graphene sheets in polymer matrix nanocomposites are important to their understanding. However, the methods available for their investigation remain a challenge. Here we report on a novel study in which the mechanical responses of a nano-sandwich model structure made of a single graphene sheet sandwiched between ultrathin polymer layers are determined using a nano-bubble inflation method. The stress-strain behavior of the graphene nano-sandwich shows that significant reinforcement is obtained at small strains and that the method also provides a measurement of the interfacial shear strength. In addition, the study provides data related to internal stresses that develop between the graphene layer and the polymer sandwich faces.
Startup shear of a highly entangled polystyrene solution deep into the nonlinear viscoelastic regime
Rheological Acta
Melt flow instability; Edge fracture; Shear banding; Nonlinear rheology; Wall slip; Entangled polymer
Forced Assembly by Multilayer Coextrusion to Create Oriented Graphene Reinforced Polymer Nanocomposites
Polymer
A potential advantage of platelet-like nanofillers as nanocomposite reinforcements is the possibility of achieving two-dimensional stiffening through planar orientation of the platelets. The ability to achieve improved properties through in-plane orientation of the platelets is a challenge and, here, we present the first results of using forced assembly to orient graphene nanoplatelets in poly(methyl methacrylate)/polystyrene (PMMA/PS) and PMMA/PMMA multilayer films produced through multilayer coextrusion. The films exhibited a multilayer structure made of alternating layers of polymer and polymer containing graphene as evidenced by electron microscopy. Significant single layer reinforcement of 118 % at a concentration of 2 wt % graphene was achieved—higher than previously reported reinforcement for randomly dispersed graphene. The large reinforcement is attributed to the planar orientation of the graphene in the individual polymer layers. Anisotropy of the stiffening was also observed and attributed to imperfect planar orientation of the graphene lateral to the extrusion flow.
Considering Viscoelastic Micromechanics for the Reinforcement of Graphene Polymer Nanocomposites
ACS Macro Letters
There has been much recent work investigating the reinforcement of glassy polymers with nanoparticles, and much excitement has been generated by some apparent synergies that suggest reinforcements greater than expected from elastic bound models. Here we show that it is necessary to consider the thermoviscoelastic response of the polymer matrix in nanocomposites (PNCs) to fully understand the reinforcement of the filler. This is especially so because polymer nanocomposites are frequently used at high fractions of the glass transition temperature Tg, where the time dependence of the polymer is significant. Therefore it is a conceptual error to examine the modulus behavior of PNCs via only elastic micromechanics. When the glass transition temperature increases due to the interactions between reinforcement and polymer, it is more reasonable to use a viscoelastic micromechanics approach to estimate the bounds on modulus behavior of PNCs. Here we use new results for grapheme oxide reinforced poly(ethyl methacrylate) (PEMA) and literature results for reinforced poly(methyl methacrylate) (PMMA) and show that the ultralow loading of graphene oxide raises the Tg of PEMA and PMMA significantly and leads to a large shift of the frequency–temperature properties of the polymer matrix. Our thermoviscoelastic approach shows that apparent extreme reinforcements can be attributed to the changing Tg of the polymer, and the corrected mechanical reinforcement from graphene oxide is much weaker than previously reported.
Mechanical responses of a polymer graphene-sheet nano-sandwich
Polymer
The interfacial mechanics and reinforcement by the graphene sheets in polymer matrix nanocomposites are important to their understanding. However, the methods available for their investigation remain a challenge. Here we report on a novel study in which the mechanical responses of a nano-sandwich model structure made of a single graphene sheet sandwiched between ultrathin polymer layers are determined using a nano-bubble inflation method. The stress-strain behavior of the graphene nano-sandwich shows that significant reinforcement is obtained at small strains and that the method also provides a measurement of the interfacial shear strength. In addition, the study provides data related to internal stresses that develop between the graphene layer and the polymer sandwich faces.
Startup shear of a highly entangled polystyrene solution deep into the nonlinear viscoelastic regime
Rheological Acta
Melt flow instability; Edge fracture; Shear banding; Nonlinear rheology; Wall slip; Entangled polymer
Forced Assembly by Multilayer Coextrusion to Create Oriented Graphene Reinforced Polymer Nanocomposites
Polymer
A potential advantage of platelet-like nanofillers as nanocomposite reinforcements is the possibility of achieving two-dimensional stiffening through planar orientation of the platelets. The ability to achieve improved properties through in-plane orientation of the platelets is a challenge and, here, we present the first results of using forced assembly to orient graphene nanoplatelets in poly(methyl methacrylate)/polystyrene (PMMA/PS) and PMMA/PMMA multilayer films produced through multilayer coextrusion. The films exhibited a multilayer structure made of alternating layers of polymer and polymer containing graphene as evidenced by electron microscopy. Significant single layer reinforcement of 118 % at a concentration of 2 wt % graphene was achieved—higher than previously reported reinforcement for randomly dispersed graphene. The large reinforcement is attributed to the planar orientation of the graphene in the individual polymer layers. Anisotropy of the stiffening was also observed and attributed to imperfect planar orientation of the graphene lateral to the extrusion flow.
Considering Viscoelastic Micromechanics for the Reinforcement of Graphene Polymer Nanocomposites
ACS Macro Letters
There has been much recent work investigating the reinforcement of glassy polymers with nanoparticles, and much excitement has been generated by some apparent synergies that suggest reinforcements greater than expected from elastic bound models. Here we show that it is necessary to consider the thermoviscoelastic response of the polymer matrix in nanocomposites (PNCs) to fully understand the reinforcement of the filler. This is especially so because polymer nanocomposites are frequently used at high fractions of the glass transition temperature Tg, where the time dependence of the polymer is significant. Therefore it is a conceptual error to examine the modulus behavior of PNCs via only elastic micromechanics. When the glass transition temperature increases due to the interactions between reinforcement and polymer, it is more reasonable to use a viscoelastic micromechanics approach to estimate the bounds on modulus behavior of PNCs. Here we use new results for grapheme oxide reinforced poly(ethyl methacrylate) (PEMA) and literature results for reinforced poly(methyl methacrylate) (PMMA) and show that the ultralow loading of graphene oxide raises the Tg of PEMA and PMMA significantly and leads to a large shift of the frequency–temperature properties of the polymer matrix. Our thermoviscoelastic approach shows that apparent extreme reinforcements can be attributed to the changing Tg of the polymer, and the corrected mechanical reinforcement from graphene oxide is much weaker than previously reported.
Graphene-based Multilayered Poly(methyl methacrylate) Nanocomposites via Forced Assembly Coextrusion
ANTEC® 2014 - Proceedings of the Technical Conference, Society of Plastics Engineers
The ability to achieve enhanced mechanical properties through in-plane orientation of platelet-like nanofillers is a challenge for nanocomposite fabrication and performance. Here we use forced assembly to orient graphene nanoplatelets in PMMA/PMMA-graphene films produced through multilayer coextrusion. Electron microscopy confirms the alternating layer structure of PMMA and PMMA containing oriented graphene. Relative reinforcement of 11 % at a concentration of 0.2 wt % graphene in the total film was achieved without loss of toughness. The reinforcement is attributed to the planar orientation and improved dispersion of the graphene as the layer thickness decreases.
Possible Matching Profiles
The following profiles may or may not be the same professor:
- Gregory B Mckenna (100% Match)
Horn Professor
Texas Tech University - Texas Tech University