Dynamic mechanical analysis of polymers in the liquid state: Use of a perforated shim stock support

This report summarizes some initial results on the use of a perforated brass shim stock support to extend the useful range of dynamic mechanical testing well over 100 degrees above the traditional limiting polymer softening points of T_g or T_m. Weak secondary relaxations were observed above T_g in both polyisobutylene (PIB) and polystyrene (PS) homopolymer, copolymer, and blend systems and above T_m in gutta percha (trans-polyisoprene). The DuPont 981 Dynamic Mechanical Analyzer (DMA)–990 Thermal Analyzer system was used to characterize these weak liquid state processes. The DMA instrument deforms the specimen in flexure, thus minimizing the shear component present in some other techniques. Specimen-coating weights are typically in the range 20–40 mg. The perforations are particularly useful for polymers having low inherent adhesion to metals or systems which are very brittle in the glassy state, e.g., low MW PS's and many methacrylates.     

ANALYTICAL SOLUTIONS FOR PEELING USING BEAM-ON-FOUNDATION MODEL AND COHESIVE ZONE

When fibrillation occurs during peeling, the normal stress in the adhesive may gradually reduce to zero at the peel front. The shear stress also reduces to zero. Classical beam-spring (or beam-on-elastic-foundation) models do not yield solutions that have these properties. With the use of a beam-on-foundation model combined with a cohesive zone in the neighborhood of the peel front, these properties can be satisfied. In order to obtain analytical solutions, peel tests are considered in which the backing has a small slope and is linearly elastic in the adhered region, and the traction law is assumed to be piecewise linear. Cases are considered with only normal stresses in the adhesive (mode I), only shear stresses (mode II), and both stresses coupled (mixed-mode behavior). Analytical solutions are obtained for displacements of the backing, forces in the backing, and stresses between the adhesive and the backing.     

Azide Reactive Dyes

Reactive dyes containing a sulphonylazide group can undergo fixation on nylon substrates by two different mechanisms. Under aqueous dyeing conditions, at or below 120d? C, the free amino end-groups of the polymer attack the sulphonylazide group with displacement of azide ion, and results in attachment of the dye to the substrate by a sulphonamide linkage. In contrast, if the dyed substrate is subjected to dry heat fixation at 170d? C, the azide group decomposes to a sulphonylnitrene species which undergoes insertion into C-H bonds of the polymer. The dye is again attached by a sulphonamide bridge, but in this case the amount of dye that can be fixed is independent of the amino end-group content of the polymer.     

Thermomechanical analysis of Tg and T > Tg transitions in polystyrene

Phenomenological softening points were measured on a series of 13 anionic, nearly monodisperse, atactic polystyrenes using a DuPont 943 thermomechanical analyzer (TMA) in a penetration mode. Although TMA cannot identify the nature of the “transition” observed as such, the results obtained support the evidence for the T_g, T_ll, and T′_ll transition in polystyrene discussed in recent literature. T_g and T_ll were found to vary with molecular weight in a systematic manner, while T′_ll could only be observed at very high molecular weight. The technique appears to be quite useful in offering rapid and reproducible information on the various transitions in the liquid state of polystyrene.     

Molecular modeling of antibody-antigen complexes between the Brucella abortus O-chain polysaccharide and a specific monoclonal antibody

A molecular model of the binding site of an anti-carbohydrateantibody (YsT9.1) has been developed using computer-assistedmodeling techniques and molecular dynamics calculations. Sequencehomologies among YsT9.1 and the Fv regions of McPC603, J539and human Bence-Jones protein REI, all of which have solvedcrystal structures, provided the basis for the modeling. Thegroove-type combining site model had a topography which wascomplementary to low energy confonners of the polysaccharide,a Brucella O-antigen, and the site could be almost completelyfilled by a pentasaccharide epitope in either of two dockingmodes. Putative interactions between this epitope and the antibodyare consistent with the known structural requirements for bindingand lead to the design of oligosaccharide inhibitors that probethe veracity of the modeled docked complex. Ultimately boththe Fv model and the docked complex will be compared with independentcrystal structures of YsT9.1 Fab with and without pentasaccharideinhibitor, currently at the stage of refinement.     

The Effect of Organic Diluent on the Extraction of Eu(III) by HEH[EHP]

ABSTRACT

Because there are fewer tools available to probe the interactions therein, the effect of the fundamental chemistry of the organic diluent on solvent extraction equilibria has been under-characterized relative to the aqueous. As a result, diluents for solvent extraction are often selected for an application not for their utility as a medium for reaction, but for other (often equally) important reasons (like low flammability). To begin to improve this imbalance in the science, twenty different diluents have been used in a study of the extraction of radiotracer ^152/154Eu³⁺ from dilute nitric acid solutions using the extractant 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]). To increase the utility of the study and to honor the memory of Professor Jan Rydberg, this investigation was conducted by a cadre of comparatively inexperienced separation scientists (who are as a result no longer inexperienced separation scientists) as a radioanalytical chemistry and solvent extraction educational exercise. Slope analysis was used to determine the apparent stoichiometry of the extracted metal complex. The results discussed in the following indicate that, while the pH dependence exhibits the expected three H⁺ exchanged per metal ion extracted, the extractant dependence suggests that the number of protonated extractant molecules in the extracted complex changes with the organic diluent. The experimentally observed “extractant dependency” ranges from 2.5 to 3.0 dimer equivalent molecules per extracted metal ion. Ironically, in the diluents exhibiting the highest apparent M:(HA)₃ stoichiometry, HEH[EHP] extracts Eu³⁺ less efficiently. Europium luminescence spectroscopy was used to probe for changes in the first coordination sphere of the complex in different diluents. A model and conceptual framework for understanding these observations is described.     

TEM Characterization of Single- and Multilayer Triol-Based Sol–Gel PZT (53/47) Thin Films

Integrated lead zirconate titanate thin films deposited on Pt/Ti/SiO₂/Si substrates using a novel triol-based route were characterized using X-ray diffraction and transmission electron microscopy. Crack-free single-layer PZT films of up to 200 nm thick were prepared by triol-based sol–gel processing onto Pt/Ti/SiO₂/Si substrates. Films ∼75 nm thick exhibited a microstructure free of pores and second phase. As film thickness increased, film texture changed from {100} to {111} perovskite. Essentially, single-phase multilayer films could be prepared by the deposition and pyrolysis of several 75 nm layers, followed by a single crystallization step. The influence of heat-treatment schedule on the microstructure and orientation of the multilayer films is discussed. Comparison has been made between multilayer films prepared using the triol-based sol and an inverted mixing order/acetic acid-based sol.     

Resampling imbalanced data to detect fake reviews using machine learning classifiers and textual-based features

Fraudulent online sellers often collude with reviewers to garner fake reviews for their products. This act undermines the trust of buyers in product reviews, and potentially reduces the effectiveness of online markets. Being able to accurately detect fake reviews is, therefore, critical. In this study, we investigate several preprocessing and textual-based featuring methods along with machine learning classifiers, including single and ensemble models, to build a fake review detection system. Given the nature of product review data, where the number of fake reviews is far less than that of genuine reviews, we look into the results of each class in detail in addition to the overall results. We recognise from our preliminary analysis that, owing to imbalanced data, there is a high imbalance between the accuracies for different classes (e.g., 1.3% for the fake review class and 99.7% for the genuine review class), despite the overall accuracy looking promising (around 89.7%). We propose two dynamic random sampling techniques that are possible for textual-based featuring methods to solve this class imbalance problem. Our results indicate that both sampling techniques can improve the accuracy of the fake review class—for balanced datasets, the accuracies can be improved to a maximum of 84.5% and 75.6% for random under and over-sampling, respectively. However, the accuracies for genuine reviews decrease to 75% and 58.8% for random under and over-sampling, respectively. We also discover that, for smaller datasets, the Adaptive Boosting ensemble model outperforms other single classifiers; whereas, for larger datasets, the performance improvement from ensemble models is insignificant compared to the best results obtained by single classifiers.