Resolving fundamental limits of adhesive bonding in microfabrication.

As electronic and optical components reach the micro- and nanoscales, efficient assembly and packaging require the use of adhesive bonds. This work focuses on resolving several fundamental issues in the transition from macro- to micro- to nanobonding. A primary issue is that, as bondline thicknesses decrease, knowledge of the stability and dewetting dynamics of thin adhesive films is important to obtain robust, void-free adhesive bonds. While researchers have studied dewetting dynamics of thin films of model, non-polar polymers, little experimental work has been done regarding dewetting dynamics of thin adhesive films, which exhibit much more complex behaviors. In this work, the areas of dispensing small volumes of viscous materials, capillary fluid flow, surface energetics, and wetting have all been investigated. By resolving these adhesive-bonding issues, we are allowing significantly smaller devices to be designed and fabricated. Simultaneously, we are increasing the manufacturability and reliability of these devices

Microcalibrator system for chemical signature and reagent delivery.

Networked systems of low-cost, small, integrable chemical sensors will enable monitoring of Nonproliferation and Materials Control targets and chemical weapons threats. Sandia-designed prototype chemical sensor systems are undergoing extended field testing supported by DOE and other government agencies. A required surety component will be verification of microanalytical system performance, which can be achieved by providing a programmable source of chemical signature(s) for autonomous calibration of analytical systems. In addition, such a controlled chemical source could be used to dispense microaliquots of derivatization reagents, extending the analysis capability of chemical sensors to a wider range of targets. We have developed a microfabricated system for controlled release of selected compounds (calibrants) into the analytical stream of microsensor systems. To minimize pumping and valve requirements of microfluidic systems, and to avoid degradation issues associated with storage of dilute solutions, we have utilized thermally labile organic salts as solid-phase reservoir materials. Reproducible deposition of tetrapropyl ammonium hydroxide onto arrays of microfabricated heating elements can provide a pair of calibration marker compounds (one fast and one slow-eluting compound) for GC analyses. The use of this microaliquot gas source array for hydrogen generation is currently under further development. The goal of the latter effort will be to provide a source of high-pressure, low viscosity GC carrier gas for Sandia's next-generation microfabricated gas-phase chemical analysis systems

Analyses of Hydrodynamic Forces on Centrifugal Pump Impellers

It has been experimentally determined by previous investigators that hydrodynamic forces can cause a centrifugal pump impeller to whirl in a volute. The present work was undertaken to develop a theoretical model of the interactions that occur between an impeller and a volute, and to identify the source of the hydrodynamic forces. Experiments were then conducted to test the predictions of the model. The theoretical analysis presents a quasi-one dimensional treatment of the flow in the volute and accounts for the disturbance at the impeller discharge that is caused by the volute. The model also considers the lack of perfect guidance through the blade passages. Extending this model allowed for the calculation of hydrodynamic force perturbations that result when the impeller whirls eccentrically in the volute. These force perturbations were shown to encourage, rather than dissipate the whirling motion. The predictions of the model gave reasonable comparisons with the experimental data obtained in this study. Further, it was experimentally observed that pressure forces acting on the front shroud of the impeller could have a major influence on the hydrodynamic force perturbations acting on an eccentrically positioned impeller.</p

Real-time discriminatory sensors for water contamination events :LDRD 52595 final report.

The gas-phase {mu}ChemLab{trademark} developed by Sandia can detect volatile organics and semi-volatiles organics via gas phase sampling . The goal of this three year Laboratory Directed Research and Development (LDRD) project was to adapt the components and concepts used by the {mu}ChemLab{trademark} system towards the analysis of water-borne chemicals of current concern. In essence, interfacing the gas-phase {mu}ChemLab{trademark} with water to bring the significant prior investment of Sandia and the advantages of microfabrication and portable analysis to a whole new world of important analytes. These include both chemical weapons agents and their hydrolysis products and disinfection by-products such as Trihalomethanes (THMs) and haloacetic acids (HAAs). THMs and HAAs are currently regulated by EPA due to health issues, yet water utilities do not have rapid on-site methods of detection that would allow them to adjust their processes quickly; protecting consumers, meeting water quality standards, and obeying regulations more easily and with greater confidence. This report documents the results, unique hardware and devices, and methods designed during the project toward the goal stated above. It also presents and discusses the portable field system to measure THMs developed in the course of this project

On the factors behind large Labrador Sea tides during the last glacial cycle and the potential implications for Heinrich events

Labrador Sea (LS) tidal elevations over the last glacial cycle are investigated in a near-global numerical model that accurately captures the present-day tides. From 65 ka to 7 ka, the modeled elevations at the debouchement point of the Hudson Strait ice stream in the LS are exceptionally large, comparable to the largest elevations seen anywhere in the present-day ocean. New numerical simulations performed for this article demonstrate that both local changes in basin geometry (e.g., ice cover over Hudson Bay) and changes outside of the LS led to enhanced LS paleotides. New simulations run at higher horizontal resolution and a considered examination of uncertainties, including uncertainties in the adopted sea level models, strengthen confidence in the robustness of the large LS paleotides. The tide model is run with both spatially uniform sea level drops (taken from curves of eustatic and Red Sea sea levels versus time) and spatially variable sea level maps (taken from two different gravitationally self-consistent viscoelastic solid earth/sea level models, which both account for ice sheet geometry). The tides are larger when the spatially variable sea level models are used. Observations in present-day Antarctica indicate that the mechanical action of tides significantly impacts the dynamics of both continental ice streams and their associated floating ice shelves. It is postulated here that large LS paleotides played a key role in the formation of Heinrich event icebergs, that is, massive discharges of ice from the LS into the glacial North Atlantic ocean. The paleotide calculations described here provide a potential explanation for why the LS region, more than any other, dominated the production of Heinrich event icebergs. Most previous hypotheses of a tidal role in climate variability and ice sheet dynamics focus on tidal mixing. In contrast, here the role of tidal mechanical forcing of ice sheets is emphasized.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/84346/1/pal_tidesheinrich.pd