Search

Your search keyword '"Grabowski, Christopher A."' showing total 36 results
Start Over Author "Grabowski, Christopher A."
36 results on '"Grabowski, Christopher A."'

6. Effect of Molecular Weight and Layer Thickness on the Dielectric Breakdown Strength of Neat and Homopolymer Swollen Lamellar Block Copolymer Films

Author

Samant, Saumil, primary, Basutkar, Monali, additional, Singh, Maninderjeet, additional, Masud, Ali, additional, Grabowski, Christopher A., additional, Kisslinger, Kim, additional, Strzalka, Joseph, additional, Yuan, Guangcui, additional, Satija, Sushil, additional, Apata, Ikeoluwa, additional, Raghavan, Dharmaraj, additional, Durstock, Michael, additional, and Karim, Alamgir, additional

Published
2020
Full Text
View/download PDF

7. KalKi: A Software-Defined IoT Security Platform

Author

Echeverria, Sebastian, primary, Lewis, Grace, additional, Mazzotta, Craig, additional, Grabowski, Christopher, additional, O'Meara, Kyle, additional, Vasudevan, Amit, additional, Novakouski, Marc, additional, McCormack, Matthew, additional, and Sekar, Vyas, additional

Published
2020
Full Text
View/download PDF

9. Deoxyribonucleic acid-based hybrid thin films for potential application as high energy density capacitors.

Author

Joyce, Donna M., Venkat, Narayanan, Ouchen, Fahima, Singh, Kristi M., Smith, Steven R., Grabowski, Christopher A., Murray, P. Terry, and Grote, James G.

Subjects
ELECTRIC properties of thin films, DIELECTRIC materials, SOLID state electronics, ENERGY storage, EXCITON theory
Abstract

Deoxyribonucleic acid (DNA) based hybrid films incorporating sol-gel-derived ceramics have shown strong promise as insulating dielectrics for high voltage capacitor applications. Our studies of DNA-CTMA (cetyltrimethylammonium) complex/sol-gel ceramic hybrid thin film devices have demonstrated reproducibility and stability in temperature- and frequency-dependent dielectric properties with dielectric constant k∼5.0 (1 kHz), as well as reliability in DC voltage breakdown measurements, attaining values consistently in the range of 300-350 V/μm. The electrical/dielectric characteristics of DNA-CTMA films with sol-gel-derived ceramics were examined to determine the critical energy storage parameters such as voltage breakdown and dielectric constant. [ABSTRACT FROM AUTHOR]

Published
2014
Full Text
View/download PDF

10. Comparing the activation energy of diffusion in bulk and ultrathin fluid films.

Author

Grabowski, Christopher A. and Mukhopadhyay, Ashis

Subjects
*DIFFUSION, *SOLUTION (Chemistry), *THIN films, *SEMICONDUCTOR doping, *SPECTRUM analysis, *MOLECULES, *MOLECULAR spectra
Abstract

We have measured the activation energy (Eact) of translational diffusion for a dissolved fluorescent dye in bulk and within an ultrathin liquid film formed on a solid substrate. The experiments were performed using the single-molecule sensitive technique of fluorescence correlation spectroscopy. From the temperature-dependent measurements, we have determined that the activation energy for a few nanometer thick fluid film increases by a factor of ≈3–4 compared to bulk liquid. The results are confirmed for two distinctly different systems in regard to molecular shape, tetrakis (2-ethylhexoxy) silane and hexadecane. [ABSTRACT FROM AUTHOR]

Published
2007
Full Text
View/download PDF

11. Diffusion of nanoparticles in semidilute and entangled polymer solutions

Author

Omari, Rami A., Aneese, Andrew M., Grabowski, Christopher A., and Mukhopadhyay, Ashis

Subjects
Polystyrene -- Chemical properties, Spectrum analysis -- Usage, Gold -- Atomic properties, Gold -- Chemical properties, Nanoparticles -- Structure, Nanoparticles -- Chemical properties, Polymers -- Structure, Polymers -- Chemical properties, Chemicals, plastics and rubber industries
Published
2009

16. Nanoelectronics: Amorphous Boron Nitride: A Universal, Ultrathin Dielectric For 2D Nanoelectronics (Adv. Funct. Mater. 16/2016)

Author

Glavin, Nicholas R., primary, Muratore, Christopher, additional, Jespersen, Michael L., additional, Hu, Jianjun, additional, Hagerty, Phillip T., additional, Hilton, Al M., additional, Blake, Austin T., additional, Grabowski, Christopher A., additional, Durstock, Michael F., additional, McConney, Michael E., additional, Hilgefort, Drew M., additional, Fisher, Timothy S., additional, and Voevodin, Andrey A., additional

Published
2016
Full Text
View/download PDF

17. Amorphous Boron Nitride: A Universal, Ultrathin Dielectric For 2D Nanoelectronics

Author

Glavin, Nicholas R., primary, Muratore, Christopher, additional, Jespersen, Michael L., additional, Hu, Jianjun, additional, Hagerty, Phillip T., additional, Hilton, Al M., additional, Blake, Austin T., additional, Grabowski, Christopher A., additional, Durstock, Michael F., additional, McConney, Michael E., additional, Hilgefort, Drew M., additional, Fisher, Timothy S., additional, and Voevodin, Andrey A., additional

Published
2016
Full Text
View/download PDF

20. Physical aging and glass transition of hairy nanoparticle assemblies

Author

Koerner, Hilmar, primary, Opsitnick, Elizabeth, additional, Grabowski, Christopher A., additional, Drummy, Larry F., additional, Hsiao, Ming-Siao, additional, Che, Justin, additional, Pike, Megan, additional, Person, Vernecia, additional, Bockstaller, Michael R., additional, Meth, Jeff S., additional, and Vaia, Richard A., additional

Published
2015
Full Text
View/download PDF

27. Electrical Control of Shape in Voxelated Liquid Crystalline Polymer Nanocomposites

Author

Guin, Tyler, Kowalski, Benjamin A., Rao, Rahul, Auguste, Anesia D., Grabowski, Christopher A., Lloyd, Pamela F., Tondiglia, Vincent P., Maruyama, Benji, Vaia, Richard A., and White, Timothy J.

Abstract

Liquid crystal elastomers (LCEs) exhibit anisotropic mechanical, thermal, and optical properties. The director orientation within an LCE can be spatially localized into voxels [three-dimensional (3-D) volume elements] via photoalignment surfaces. Here, we prepare nanocomposites in which both the orientation of the LCE and single-walled carbon nanotube (SWNT) are locally and arbitrarily oriented in discrete voxels. The addition of SWNTs increases the stiffness of the LCE in the orientation direction, yielding a material with a 5:1 directional modulus contrast. The inclusion of SWNT modifies the thermomechanical response and, most notably, is shown to enable distinctive electromechanical deformation of the nanocomposite. Specifically, the incorporation of SWNTs sensitizes the LCE to a dc field, enabling uniaxial electrostriction along the orientation direction. We demonstrate that localized orientation of the LCE and SWNT allows complex 3-D shape transformations to be electrically triggered. Initial experiments indicate that the SWNT–polymer interfaces play a crucial role in enabling the electrostriction reported herein.

Published
2018
Full Text
View/download PDF

31. Physical aging and glass transition of hairy nanoparticle assemblies.

Author

Koerner, Hilmar, Opsitnick, Elizabeth, Grabowski, Christopher A., Drummy, Larry F., Hsiao, Ming-Siao, Che, Justin, Pike, Megan, Person, Vernecia, Bockstaller, Michael R., Meth, Jeff S., and Vaia, Richard A.

Subjects
GRAFT copolymers, GLASS transitions, POLYMER degradation, POLYMERIC nanocomposites, POLYSTYRENE, DIELECTRIC properties, SURFACE morphology, MOLECULAR self-assembly
Abstract

ABSTRACT Matrix free assemblies of polymer-grafted, 'hairy' nanoparticles (aHNP) exhibit novel morphology, dielectric, and mechanical properties, as well as providing means to overcome dispersion challenges ubiquitous to conventional polymer-inorganic nanocomposite blends. Physical aging of the amorphous polymer glass between the close-packed nanoparticles (NPs) will dominate long-term stability; however, the energetics of volume recovery within the aHNPs is unknown. Herein, we compare glass transition temperature ( Tg) and enthalpy recovery of aHNPs to NP-polymer blends, across different nano-silica loadings (0-50 v/v%) and canopy architecture of polystyrene (PS) grafted silica. For aHNPs, the grafting of PS to silica imposes an additional design constraint between silica volume fraction, graft density, and graft molecular weight. At low and intermediate silica volume fraction, the Tg of blended nanocomposites is independent of silica content, reflecting a neutral polymer-NP interface. For aHNPs, the Tg decreases with silica content, implying that chain tethering decreases local segment density more than the effect of molecular weight or polymer-NP interactions. Additionally, the Tg of the aHNPs is higher than a linear matrix of comparable molecular weight, implying a complementary effect to local segment density that constrains cooperativity. In contrast, enthalpy recovery rate in the blend or aHNP glass is retarded comparably. In addition, a cross-over temperature, Tx, emerges deep within the glass where the enthalpy recovery process of all nanocomposites becomes similar to linear unfilled matrices. Differences between structural recovery in aHNP and blended nanocomposites occur only at the highest silica loadings (∼ 50 v/v%), where enthalpy recovery for aHNPs is substantially suppressed relative to the blended counterparts. The absence of physical aging at these loadings is independent of brush architecture (graft density or molecular weight of tethered chains) and indicates that the impact of chain tethering on effective bulk structural relaxation starts to appear at particle-particle surface separations on the order of the Kuhn length. Overall, these observations can be understood within the context of how three separate structural characteristics impact local segment density and relaxation processes: the dimension and architecture of the tethered polymer chains, the separation between NP surfaces, and the confinement imposed by chain tethering and space filling within the aHNP. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 319-330 [ABSTRACT FROM AUTHOR]

Published
2016
Full Text
View/download PDF

33. Dielectric performance of high permitivity nanocomposites: impact of polystyrene grafting on BaTiO3and TiO2

Author

Grabowski, Christopher A., Fillery, Scott P., Koerner, Hilmar, Tchoul, Maxim, Drummy, Lawrence, Beier, Christopher W., Brutchey, Richard L., Durstock, Michael F., and Vaia, Richard A.

Abstract

AbstractPolymer nanocomposites are a promising concept to improve energy storage density of capacitors, but realizing their hypothetical gains has proved challenging. The introduction of high permittivity fillers often leads to reduction in breakdown strength due to field exclusion, which intensifies the applied electric field within the polymer matrix near nanoparticle interfaces. This has prompted research in developing new nanoparticle functionalization chemistries and processing concepts to maximize particle separation. Herein, we compare the dielectric performance of blended nanocomposites to matrix free assemblies of hairy (polymer grafted) nanoparticles (HNPs) that exhibit comparable overall morphology. The dielectric breakdown strength of polystyrene grafted BaTiO3(PS@BaTiO3) systems was over 40% greater than a blended nanocomposite with similar loading (~25% v/v BaTiO3). Hairy nanoparticles with TiO2cores followed similar trends in breakdown strength as a function of inorganic loading up to 40% v/v. Dielectric loss for PS@BaTiO3HNPs was 2–5 times lower than analogous blended films for a wide frequency spectrum (1 Hz to 100 kHz). For content above 7% v/v, grafting the polymer chains to the BaTiO3significantly improved energy storage efficiency. Overall this study indicates that polymer grafting improves capacitor performance relative to direct blending in likely two ways: (1) by mitigating interfacial transport to lower dielectric loss, irrespective of the dielectric contrast between matrix and nanoparticle, and (2) by restricting particle–particle hot-spots by establishing a finite minimum particle separation when the dielectric contrast between matrix and nanoparticle is large.

Published
2016
Full Text
View/download PDF

34. Synthesis of highly dispersed, block copolymer-grafted TiO2 nanoparticles within neat block copolymer films.

Author

Hailu, Shimelis T., Samant, Saumil, Grabowski, Christopher, Durstock, Michael, Karim, Alamgir, and Raghavan, Dharmaraj

Subjects
BLOCK copolymers, CHEMICAL synthesis, TITANIUM oxides synthesis, DISPERSION (Chemistry), NANOPARTICLES, POLYMER research
Abstract

ABSTRACT The objective of the study is to formulate exclusive block copolymer (BCP) nanocomposites by dispersing bcp end-grafted nanoparticles (bcp- g-nps) of PMMA- b-PS- g-TiO2 within PS- b-PMMA matrix. PMMA- b-PS- g-TiO2 is synthesized using a 'grafting-to' approach and characterized by XPS and TGA to establish that the copolymer chains were bonded to NPs. Good dispersion of bcp- g-nps in PMMA and PS-PMMA bcp films is observed, in contrast to poor dispersion in PS films. In PS-PMMA films, the compatible and identical bcp nature of the end-grafted polymer, and large NP size caused it to span across entire PS-PMMA domains. Poor and good dispersion in PS and PMMA matrices, respectively, can be rationalized by the fact that NPs interactions are driven by the PMMA at the outer corona of the bcp- g-nps. Developing bcp- g-nps as a strategic route to preparation of highly dispersed high permittivity NPs like titanium dioxide (TiO2) in bcp matrix can have important ramifications for energy storage devices. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 468-478 [ABSTRACT FROM AUTHOR]

Published
2015
Full Text
View/download PDF

36. Back to the Nest.

Author

Grabowski, Christopher

Subjects
*POOR children, *HUMANITARIAN assistance, *NONGOVERNMENTAL organizations, *CHILDREN, *INTERNATIONAL agencies
Abstract

This is an article that focuses on the efforts of Aschiana, an Afghan non-governmental organization, in helping children who are forced to panhandle on the street. Street-working children are one of the realities of post-war Afghanistan. Estimated to number some 37,000 in Kabul, sometimes missing one or both parents, they are forced to panhandle, work at low-paying menial jobs, and scrounge for basic necessities. Working with Terre des hommes, a Geneva-based group devoted to aiding children around the world, it runs a half-dozen drop-in centres in Kabul, helping about 2,600 boys and girls between the ages of 6 and 16. It also gives street children one simple meal a day. And Nick Putz, a circus arts teacher from London, England, gave a workshop on juggling, clowning and other circus skills.

Published
2004

Catalog

Books, media, physical & digital resources
See catalog results