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Search Publications by: Christopher Stafford (Fed)

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Displaying 151 - 175 of 203

Measuring the Modulus of Hydrated Contact Lenses via Surface Wrinkling

April 6, 2008
Author(s)
Jun Y. Chung, Young Jong Lee, Peyton Hopson, Michael J. Fasolka, Christopher Stafford
One of the most important considerations in the evaluation of hydrogels for biomedical and contact lens applications is the elastic modulus. The elastic modulus relates to several important factors including flexibility, comfort, adhesion, swelling

Quantifying Interfacial Adhesion in Transfer Printing via a Cantilever Peel Test

April 6, 2008
Author(s)
Jiong Liu, Jun Y. Chung, Christopher Stafford
Transfer printing has been demonstrated as a fabrication method for flexible organic electronics. The transfer printing process relies on the differential adhesion of a printable layer (PL) that is pressed between two substrates: transfer substrate (TS)

Synthesis and Characterization of Polymer Brushes from PDMS Surfaces

April 6, 2008
Author(s)
Heqing Huang, Adam J. Nolte, Jun Y. Chung, Christopher Stafford
In recent years, poly(dimethylsiloxane) (PDMS) has found increased application in the areas of microfluidic devices, chromatographic packing materials and membranes, as well as in medical and drug delivery devices. However, the hydrophobic surface of PDMS

High throughput adhesion testing using a modified edge lift-off test

February 17, 2008
Author(s)
Jiong Liu, Martin Chiang, Michael J. Fasolka, Christopher Stafford
The strength of an adhesively bonded joint depends on a host of factors such as surface treatment, roughness, materials properties, cure conditions and environmental variables. Therefore testing of adhesion within this large parameter space can be very

JKR Adhesion Testing Between Biologically Relevant Surfaces

February 17, 2008
Author(s)
Adam J. Nolte, Heqing Huang, Christopher Stafford
In this work we report recent observations obtained using an adhesion testing device that utilizes the contact mechanics theory of Johnson, Kendall, and Roberts (JKR). Our goal is to develop a system capable of measuring adhesive forces between

Single cantilever peel test for analysis of adhesion strength in nanotransfer printing

February 17, 2008
Author(s)
Deuk Y. Lee, Gottlieb Oehrlein, Daniel R. Hines, Jiong Liu, Jun Y. Chung, Christopher Stafford, Christopher Soles, Eric K. Lin
Nanotransfer printing (NTP) has attracted much attention as a method for fabricating nanoscale structures using materials that are not generally compatible with conventional lithographic techniques. For NTP of a polymer film to a polymer substrate, thermal

Characterizing Polymer Brushes via Surface Wrinkling

November 21, 2007
Author(s)
Heqing Huang, Jun Y. Chung, Adam J. Nolte, Christopher M. Stafford
We present the application of surface wrinkling to measure the properties of polymer brush layers tethered to the surface of a deformable silicone substrate. It is demonstrated that the wavelength of the wrinkling pattern linearly increases with the length

Dynamics of Confined Polymer Films Measured via Thermal Wrinkling

October 19, 2007
Author(s)
Kirt A. Page, Derek L. Patton, Rui Huang, Christopher Stafford
In the past several years there have been a number of advances in the understanding of the physics of polymer thin films. However, there still remains a wide range of opportunities to further this understanding through the development of measurement tools

NCMC Workshop ReportNCMC-10: Persistent Challenges in Combinatorial Materials Science

February 1, 2007
Author(s)
Michael J. Fasolka, Carol E. Laumeier, Kathryn L. Beers, Christopher M. Stafford
Tremendous advances in the development and application of combinatorial and high-throughput methods for materials research have been accomplished over the past 15 years. Despite these accomplishments, today s combinatorial materials science is met by some

Anisotropic Wetting on Tunable Micro-Wrinkled Surfaces

January 1, 2007
Author(s)
Jun Y. Chung, Jeffrey Youngblood, Christopher M. Stafford
We demostrate that the buckling instability technique is promising for studying wettability because key elements of surface topography such as surface roughness can be precisely controlled by simple changes in experimental conditions. For demonstration, we

Buckling Modes of Elastic Thin Films on Elastic Substrates

January 1, 2007
Author(s)
Haixia Mei, Jun Y. Chung, Honghui Yo, Christopher Stafford, Rui Huang
Subject to compression, a thin elastic film bonded to an elastic substrate can buckle. Two buckling modes have been observed. On a stiff substrate, the film buckles when it is partly delaminated from the substrate, resulting in localized buckle patterns

Effect of Surface Properties on Wrinkling of Ultrathin Films

January 1, 2007
Author(s)
Rui Huang, Christopher Stafford, B D. Vogt
Thin films bonded to compliant substrates often develop wrinkles when subjected to an applied or inherent compressive stress. This paper presents a bilayer model to account for surface effects on the wrinkling of ultrathin solid films. Assuming a surface

Fabrication Strategies for Producing Gradient Roughness Libraries

January 1, 2007
Author(s)
Christopher Stafford, Jun Y. Chung, Xuesong Hu, Heqing Huang
New technologies, such as flexible electronics and functional coatings systems, consist of hierarchical structures fabricated out of combinations of both soft and hard materials, with each material type lending unique properties and performance

Wetting Behavior on Microscale Wrinkled Surfaces

January 1, 2007
Author(s)
Jun Y. Chung, Christopher M. Stafford
We present a systematic study of the wetting behavior on the anisotropic microstructure having a simple sinusoidal profile. The micro-patterned surface was generated by using the buckling-based technique, and its wetting properties were examined by contact

Elastic Moduli of Ultrathin Amorphous Polymer Films

July 1, 2006
Author(s)
Christopher Stafford, C Harrison, D Julthongpiput, B D. Vogt
The elastic moduli of ultrathin poly(styrene) and poly(methylmethacrylate) films of thickness ranging from 200 nm to 5 nm were investigated using a buckling-based metrology. Below 40 nm, the apparent modulus of the PS and PMMA films decreases dramatically

Wrinkling of Ultrathin Polymer Films

June 1, 2006
Author(s)
Rui Huang, Christopher Stafford, B D. Vogt
This paper presents a bilayer model to account for surface effects on the wrinkling of ultrathin polymer films. Assuming a surface layer of finite thickness, effects of surface properties on the critical strain, the equilibrium wavelength, and the wrinkle

Probing the Interfacial Adhesion Strength in Compositional Libraries of Epoxy Films

May 1, 2006
Author(s)
Christopher Stafford, J Y. Kim, D Kawaguchi, Gareth Royston, Martin Chiang
We are developing a measurement platform, based on the edge lift-off test geometry, geared towards combinatorial and high-throughput (C&HT) assessment of interfacial reliability in thermally cured epoxy materials. A critical parameter space to be explored

Measuring the Modulus of Soft Polymer Networks via a Buckling-Based Metrology

April 1, 2006
Author(s)
Elizabeth A. Wilder, Shu Guo, Sheng Lin-Gibson, Michael J. Fasolka, Christopher Stafford
We present a new method for measuring the modulus of soft polymer networks (E 10 MPa).This metrology utilizes compression-induced buckling of a sensor film applied to the surface of the specimen,where the periodic buckling wavelength, assessed rapidly by

Estimation of the Interfacial Adhesion Strength in Compositional Libraries of Epoxy Films

February 22, 2006
Author(s)
Jae Hyun Kim, Martin Y. Chiang, D Kawaguchi, Gareth Royston, Christopher M. Stafford
At the NIST Combinatorial Methods Center (NCMC), we have designed, developed, and demonstrated a combinatorial approach to the edge delamination test to char-acterize the adhesion of thin polymer films. This test is based on fracture of a film/substrate
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