Jim Holbery

Study of the Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/Cellulose Nanowhisker Composites Prepared by Solution Casting and Melt Processing

In this study cellulose nanowhiskers (CNW) were prepared by sulfuric acid hyrolysis from microcrystalline cellulose (MCC). The biopolymer composites of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/CNW, was fabricated by solution casting using N,N-dimethylformamide (DMF) as the solvent. Homogeneous dispersion of the whiskers was achieved and the composites exhibited improved tensile strength and modulus and increased glass transition temperature. The melt processing (extrusion and injection molding) of PHBV/CNW composites was also attempted. Despite using polyethylene glycol (PEG) as a compatibilizer, CNW agglomerates formed during freeze-drying could not be broken and well dispersed by the extrusion process due to the large surface area and the polar nature of CNW. As a result, the melt processed PHBV/CNW composites exhibited decreased strength and constant glass transition temperature, a typical trend of microparticle filled polymer systems. MCC was also treated by high-speed mechanical homogenizer to reduce its particle size down to nanoscale range. The homogenized MCC (HMCC) was blended with PHBV by melt processing with the same conditions. The obtained composites were found to have similar properties as the melt-processed PHBV/CNW composites due to poor HMCC dispersion. To the best of our knowledge, PHBV/ CNW system has not been studied so far. The treatment of MCC with high-speed homogenizer has also not been reported. This study augments the research on CNW nanocomposites.

Experimental determination of scanning probe microscope cantilever spring constants utilizing a nanoindentation apparatus

A rapid, nondestructive, and accurate method for determining the normal spring constants of scanning probe microscopy cantilevers is presented. Spring constants are determined using a commercial combination atomic force microscope and nanoindentation apparatus configured with a W-indenter tip geometrically configured into either a scanning tunneling microscope pointed tip or chisel shape that may be placed onto the cantilever of interest with high accuracy. A load is applied to the cantilever tip and the corresponding displacement is measured. From the force–displacement curve, the spring constant is determined. For cantilevers with spring constants greater than 1 N/m, the derived spring constants are believed to be accurate to within ±10%, with better accuracy for stiffer levers. This method has been used to measure the stiffness of cantilevers from several manufacturers.

Fiber Length and Orientation in Long-Fiber Injection-Molded Thermoplastics. Part I: Modeling of Microstructure and Elastic Properties

This article develops a methodology to predict the elastic properties of long-fiber injection-molded thermoplastics (LFTs). The corrected experimental fiber length distribution and the predicted and experimental orientation distributions were used in modeling to compute the elastic properties of the composite. First, from the fiber length distribution (FLD) data in terms of number of fibers versus fiber length, the probability density functions were built and used in the computation. The two-parameter Weibulls distribution was also used to represent the actual FLD. Next, the Mori—Tanaka model that employs the Eshelbys equivalent inclusion method was applied to calculate the stiffness matrix of the aligned fiber composite containing the established FLD. The stiffness of the actual as-formed composite was then determined from the stiffness of the computed aligned fiber composite that was averaged over all possible orientations using the orientation averaging method. The methodology to predict the elastic properties of LFTs was validated via experimental verification of the longitudinal and transverse moduli determined for long glass fiber injection-molded polypropylene specimens. Finally, a sensitivity analysis was conducted to determine the effect of a variation of FLD on the composite elastic properties. Our analysis shows that it is essential to obtain an accurate fiber orientation distribution and a realistic fiber length distribution to accurately predict the composite properties.

Alloying MoS2 with Al and Au: structure and tribological performance

Mechanical and tribological properties of MoS2 alloyed with Al and Au have been analysed using pin-on-disk. X-ray diffraction (XRD) and TEM to determine the relationship between coating structure and performance. Physical effects by the alloying partner, atomic percentage and variation of deposition parameters on the final behaviour of the coatings are evaluated. XRD and TEM analyses indicate two different structures exist in the MoS2 alloys studied: MoS2–Au alloys deposited from a compound target exhibited periodic distributed particles of 2.5–6 nm while MoS2–Al coatings evolved with a multi-layer architecture. XRD analysis indicates interfacial mixing and roughness present within the individual layers are greatest near 1 mTorr.

Fabrication of Novel Transparent Touch Sensing Device via Drop-on-Demand Inkjet Printing Technique

UNLABELLED A novel transparent touch sensor was fabricated with a drop-on-demand inkjet printing technique on borosilicate glass and flexible polyethylene terephthalate (PET) substrates. Conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT PSS) and dielectric poly(methylsiloxane) were deposited on a desired area to form a capacitive touch sensor structure. The properties of the printed sensors (optical transparency, electrical resistance and touch sensing performance) were investigated with varying PEDOT PSS printing passes. A novel transparent touch sensor fabricated with an all-inkjet-printing method is demonstrated for the first time. This process holds industrially viable potential to fabricate transparent touch sensors with an inkjet printing technique on both rigid and flexible substrates for a wide range of applications.

Opportunity Analysis for Recovering Energy from Industrial Waste Heat and Emissions

United States industry consumed 32.5 Quads (34,300 PJ) of energy during 2003, which was 33.1% of total U.S. energy consumption (EIA 2003 Annual Energy Review). The U.S. industrial complex yields valuable goods and products. Through its manufacturing processes as well as its abundant energy consumption, it supports a multi-trillion dollar contribution to the gross domestic product and provides millions of jobs in the U.S. each year. Industry also yields waste products directly through its manufacturing processes and indirectly through its energy consumption. These waste products come in two forms, chemical and thermal. Both forms of waste have residual energy values that are not routinely recovered. Recovering and reusing these waste products may represent a significant opportunity to improve the energy efficiency of the U.S. industrial complex. This report was prepared for the U.S. Department of Energy Industrial Technologies Program (DOE-ITP). It analyzes the opportunity to recover chemical emissions and thermal emissions from U.S. industry. It also analyzes the barriers and pathways to more effectively capitalize on these opportunities. A primary part of this analysis was to characterize the quantity and energy value of the emissions. For example, in 2001, the industrial sector emitted 19% of the U.S. greenhouse gases (GHG) through its industrial processes and emitted 11% of GHG through electricity purchased from off-site utilities. Therefore, industry (not including agriculture) was directly and indirectly responsible for emitting 30% of the U.S. GHG. These emissions were mainly comprised of carbon dioxide (CO2), but also contained a wide-variety of CH4 (methane), CO (carbon monoxide), H2 (hydrogen), NMVOC (non-methane volatile organic compound), and other chemicals. As part of this study, we conducted a survey of publicly available literature to determine the amount of energy embedded in the emissions and to identify technology opportunities to capture and reuse this energy. As shown in Table E-1, non-CO2 GHG emissions from U.S. industry were identified as having 2180 peta joules (PJ) or 2 Quads (quadrillion Btu) of residual chemical fuel value. Since landfills are not traditionally considered industrial organizations, the industry component of these emissions had a value of 1480 PJ or 1.4 Quads. This represents approximately 4.3% of the total energy used in the United States Industry.

Accelerated cure of thermoset fiber composites utilizing latent cure agents

Cure agents including micro-pulverized dicyandiamide, aliphatic amine, imidazole, dyhydrazide, and ureas have been formulated with DGEBA (diglycidyl ether of bisphenol-A) epoxides to provide preimpregnated fiberglass prepregs suitable for the rapid production of structural composites under an aggressive elevated temperature cure schedule (10 min at 110°C). Formulations have been developed utilizing in part Taguchi orthogonal experimental arrays and compared to existing chemistries. Chemical formulation properties including heat of reaction, viscosity, glass transition, process parameter determination, and impact of environmental exposure have been investigated. Formulations developed within this body of work appear to outperform current commercial systems for the production of structural composites rapidly processed at a relatively low temperature.

Silicones for Stretchable and Durable Soft Devices: Beyond Sylgard-184

This paper identifies and characterizes silicone elastomers that are well-suited for fabricating highly stretchable and tear-resistant devices that require interfacial bonding by plasma or UV ozone treatment. The ability to bond two or more pieces of molded silicone is important for creating microfluidic channels, chambers for pneumatically driven soft robotics, and other soft and stretchable devices. Sylgard-184 is a popular silicone, particularly for microfluidic applications. However, its low elongation at break (∼100% strain) and moderate tear strength (∼3 N/mm) make it unsuitable for emerging, mechanically demanding applications of silicone. In contrast, commercial silicones, such as Dragon Skin, have excellent mechanical properties yet are difficult to plasma-bond, likely because of the presence of silicone oils that soften the network yet migrate to the surface and interfere with plasma bonding. We found that extracting silicone oligomers from these soft networks allows these materials to bond but only when the Shore hardness exceeds a value of 15 A. It is also possible to mix highly stretchable silicones (Dragon Skin and Ecoflex) with Sylgard-184 to create silicones with intermediate mechanical properties; interestingly, these blends also only bond when the hardness exceeds 15 A. Eight different Pt-cured silicones were also screened; again, only those with Shore hardness above 15 A plasma-bond. The most promising silicones from this study are Sylgard-186 and Elastosil-M4130 and M4630, which exhibit a large deformation (>200% elongation at break), high tear strength (>12 N/mm), and strong plasma bonding. To illustrate the utility of these silicones, we created stretchable electrodes by injecting a liquid metal into microchannels created using such silicones, which may find use in soft robotics, electronic skin, and stretchable energy storage devices.

Nanoscale mechanical degradation of titanium/PETI-5 adhesive interface due to thermal exposure

Titanium substrates coated with silicate/zirconate sol-gel and plasma sputtered chromium have been adhered using a combined PETI-5 polyimide psuedo-thermoplastic primer/adhesive system. Composite laminates were exposed to thermal aging up to 2000 hours at 194°C, subsequently interface analysis was performed using nanoindentation to determine material modulus degradation and plastic deformation changes. Inhomogeneities at the interface mandated that both low loads (as low as 25 μN) and a 90°cube-corner diamond tip be utilized to obtain sub-micron resolution. Sol-gel coated and chromium coated titanium substrates exhibited a pronounced step-wise gradient across the interface dependent upon the indent load level and corresponding depth. Thermal aging produced an increase in both the PETI-5 primer and adhesive modulus by 20% and upwards of 30%, respectively. Sol-gel modulus increased by approximately 15% with environmental exposure and at an exposure level at 1000 hours, the chromium modulus increased approximately 20%. An decrease in plastic deformation resulting from thermal aging observed and reported, combined with material modulus alteration, is thought to be critical in predicting the overall life in adhesion joints within mission critical aerospace structures.

Nanoscale Mechanical Characterization of the Effect of Thermal Aging on Titanium/PETI-5 Adhesive Interface Properties

Abstract Titanium substrates coated with silicate/zirconate sol-gel and plasma sputtered chromium have been adhered using a combined PETI-5 polyimide psuedo-thermoplastic primer/adhesive system. Composite laminates were exposed to thermal aging up to 2000 hours at 194°C and subsequently nanoindentation testing was performed across each interface to determine material modulus degradation and plastic deformation changes. The procedure to analyze complex interfaces using nanoindentation are explained in detail including experimental set-up, analysis, and imaging; for example, inhomogeneities at the interface mandated that both low loads (as low as 25 μN) and a 90° cube-corner diamond tip be utilized to obtain sub-micron resolution. Thermal aging resulted in an increase in PETI-5 primer and adhesive modulus by 15% and upwards of 30%, respectively, and the sol-gel modulus increased by approximately 10%. An exposure level at 1000 hours showed a 20% increase in the chromium modulus. Large increases in plastic deformation were observed in the polymeric materials likely due to chain embrittlement.