Capillary leveling of stepped films with inhomogeneous molecular mobility

A homogeneous thin polymer film with a stepped height profile levels due to the presence of Laplace pressure gradients. Here we report on studies of polymeric samples with precisely controlled, spatially inhomogeneous molecular weight distributions. The viscosity of a polymer melt strongly depends on the chain length distribution; thus, we learn about thin-film hydrodynamics with viscosity gradients. These gradients are achieved by stacking two films with different molecular weights atop one another. After a sufficient time these samples can be well described as having one dimensional viscosity gradients in the plane of the film, with a uniform viscosity normal to the film. We develop a hydrodynamic model that accurately predicts the shape of the experimentally observed self-similar profiles. The model allows for the extraction of a capillary velocity, the ratio of the surface tension and the viscosity, in the system. The results are in excellent agreement with capillary velocity measurements of uniform mono- and bi-disperse stepped films and are consistent with bulk polymer rheology.Comment: Accepted for publication in Soft Matter, Themed Issue on "The Geometry and Topology of Soft Materials

Self-Similarity and Energy Dissipation in Stepped Polymer Films

The surface of a thin liquid film with nonconstant curvature is unstable, as the Laplace pressure drives a flow mediated by viscosity. We present the results of experiments on one of the simplest variable curvature surfaces: a stepped polymer film. Height profiles are measured as a function of time for a variety of molecular weights. The evolution of the profiles is shown to be self-similar. This self-similarity offers a precise measurement of the capillary velocity by comparison with numerical solutions of the thin film equation. We also derive a master expression for the time dependence of the excess free energy as a function of the material properties and film geometry. The experiment and theory are in excellent agreement and indicate the effectiveness of stepped polymer films to elucidate nanoscale rheological properties.Comment: 5 pages, 4 figures, article accepted for publication in Physical Review Letter

Capillary-driven flow induced by a stepped perturbation atop a viscous film

Thin viscous liquid films driven by capillarity are well described in the lubrication theory through the thin film equation. In this article, we present an analytical solution of this equation for a particular initial profile: a stepped perturbation. This initial condition allows a linearization of the problem making it amenable to Fourier analysis. The solution is obtained and characterized. As for a temperature step in the heat equation, self-similarity of the first kind of the full evolution is demonstrated and a long-term expression for the excess free energy is derived. In addition, hydrodynamical fields are described. The solution is then compared to experimental profiles from a model system: a polystyrene nanostep above the glass transition temperature which flows due to capillarity. The excellent agreement enables a precise measurement of the capillary velocity for this polymeric liquid, without involving any numerical simulation. More generally, as these results hold for any viscous system driven by capillarity, the present solution may provide a useful tool in hydrodynamics of thin viscous films.Comment: Accepted for publication in Physics of Fluid

Return on investment in the public sector

In an environment of scarce resources and rising federal deficits the people not only expect, but demand greater accountability for the spending of public funds. This demand has created a trend in the public sector, not only in the United States, but worldwide as well, towards the importation of private sector business practices to improve accountability-oriented analysis. One example is increased emphasis on return on investment (ROI) analysis in public sector organizations. Development and application of ROI analysis is challenging in the public sector since most government organizations do not generate profit necessary for calculation of ROI in the manner in which it is done in the private sector. This thesis develops the methodology necessary for use of ROI analysis in the public sector. ROI methodology is applied for test evaluation with the Space and Naval Warfare Systems Command (SPAWAR) in San Diego. The test demonstrates that ROI can be applied successfully to assess the relative efficiency of value-added work and to improve the process of choosing between investment alternatives. Properly designed ROI analysis reveals how and for what goods and services money is spent and provides a means for comparing the value derived from investment and work performed.http://archive.org/details/returnoninvestme109451317Lieutenant, United States NavyApproved for public release; distribution is unlimited

Development and validation of a technoeconomic analysis tool for early-stage evaluation of biorenewable processes

The production of bio-based chemicals has received tremendous attention in recent years, but little has been done to understand the broad patterns of the economics of different processes for making these molecules. The diversity of potential chemicals simultaneously makes such an understanding both important and difficult to glean during these early-stages. By using cost correlations and standard scale-factors, a spreadsheet-based early-stage cost estimation tool was developed. The tool, named BioPET (Biorenewables Process Evaluation Tool), allows users to specify up to seven primary unit operations (fermentation, separation, three catalytic stages, and purification), and basic defining inputs for each operation. With these inputs, BioPET computes an estimated minimum selling price for the pathway of interest. Validation of BioPET was conducted by comparing results to literature values and a commercial economic analysis tool for three molecules: ethanol, succinic acid, and adipic acid. BioPET produced virtually identical prices to SuperPro Designer® for the three chemicals, although the costs were not identically distributed amongst the categories; BioPET produced estimates that were within 40% of other literature values at low feedstock costs, and within 5% at high feedstock costs

Coupling Strategies for the Synthesis of Peptide-Oligonucleotide Conjugates for Patterned Synthetic Biomineralization

This work describes preparation strategies for peptide-oligonucleotide conjugates that combine the self-assembling behavior of DNA oligonucleotides with the molecular recognition capabilities of peptides. The syntheses include a solution-phase fragment coupling reaction and a solid-phase fragment coupling strategy where the oligonucleotide has been immobilized on DEAE Sepharose. The yield of four coupling reagents is evaluated, two reagents in water, EDC (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride) and DMTMM (4-(4,6-dimethoxy[1,3,5]triazin-2-yl)-4-methyl-morpholinium chloride), and two in dimethylformamide (DMF), PyBOP ((Benzotriazol-1-yloxy) tripyrrolidinophosphonium hexafluorophosphate) and HBTU (O-benzotriazole-N,N,N′,N′-tetramethyluronium hexafluorophosphate), while the oligonucleotide fragment is either in solution or immobilized on DEAE. These coupling strategies rely on an unprotected 5′ amino linker on the oligonucleotide reacting with the peptide C-terminus. The peptide, selected from a combinatorial library for its gold-binding behavior, was 12 amino acids long with an N-terminus acetyl cap. Formation of the conjugates was confirmed by gel electrophoresis and mass spectrometry while molecular recognition functionality of the peptide portion was verified using atomic force microscopy. Solution-phase yields were superior to their solid-phase counterparts. EDC resulted in the highest yield for both solution-phase (95%) and solid-phase strategies (24%), while the DMF-based reagents, PyBOP and HBTU, resulted in low yields with reduced recovery. All recoverable conjugates demonstrated gold nanoparticle templating capability