John G. Tsavalas

Water-based crosslinkable coatings via miniemulsion polymerization of acrylic monomers in the presence of unsaturated polyester resin

Hybrid miniemulsion polymerization was performed with a three-component acrylic system of methyl methacrylate, butyl acrylate, and acrylic acid in the presence of a Bayer® Roskydal TPLS2190 unsaturated polyester resin. Latexes were obtained in which the polyester resin was grafted to the acrylic polymer, forming a water-based crosslinkable coating. Grafting between the resinous component and the acrylic polymer is a feature different from the work of others who have attempted to combine the properties of both systems in water-based blends. Both emulsions and latexes were shelf-stable for over 6 months, shear-stable, and resistant to at least one freeze/thaw cycle. Resin-to-monomer ratios were studied as high as 1 : 1 (wt : wt), and total emulsion solids, as high as 45%. Monomer droplet and latex particle sizes were similar, suggesting evidence of the preponderance of droplet nucleation. A high level of crosslinking (>70%) during polymerization was observed in this particular hybrid system in contrast to those involving alkyd or polyurethane resins (<5%). Films, both homogeneous and hard, were achieved with exceptional adhesion. Electron microscopy showed the hybrid particle morphology to have internal domains of polyester resin in an acrylic matrix.

Hydroplasticization of Polymers: Model Predictions and Application to Emulsion Polymers

The plasticization of a polymer by solvent has a dramatic impact on both its thermal and mechanical behavior. With increasing demand for zero volatile organic compound materials and coatings, water is often the sole solvent used both in the polymer synthesis and in formulation and application; latex colloids derived from emulsion polymerization are a good example. The impact of water on the glass transition temperature of a polymer thus becomes a critical physical property to predict. It has been shown here that in order to do so, one simply needs the dry state glass transition temperature (T(g)) of the (co)polymer, the T(g) of water, and the saturated weight fraction of water for the sample in question. Facile calculation of the later can be achieved using water sorption data and the group additivity method. With these readily available data, we show that a form of the Flory-Fox equation can be used to predict the hydroplasticized state of copolymers in exceptional agreement with direct experimental measurement. Furthermore, extending the prediction to include the impact of the degree of ionization for pH responsive components, only with extra knowledge of the pK(a), was also validated by experiment.

Limiting Conversion Phenomenon in Hybrid Miniemulsion Polymerization

A phenomenon seemingly unique to hybrid miniemulsion polymerization was observed where monomer conversion would either plateau at a limiting value or quickly switch to a dramatically lesser rate. This phenomenon has been attributed to a combination of three factors. The first factor is the degree to which the monomer and resinous component are compatible. Second is the resultant particle morphology after circa 80% monomer conversion, which roughly corresponds to the portion of reaction where this morphology is established. The third factor is the degree of interaction between the growing polymer and resin (grafting). Of these three, the first two factors were found much more significant in contributing to the limiting conversion. When particle morphology was found to be core/shell, a hard shell (high Tg polymer, PMMA) was found to form a barrier against newly formed initiator radicals derived in the aqueous‐phase after appropriate conversion. Residual unreacted monomer solubilized in the resin‐dominated particle core was thereafter unreachable by new radicals; hence a limited monomer conversion. In cases where the acrylic polymer (PBA) exhibited a glass transition significantly below the reaction temperature, instead of a core/shell morphology one where the acrylic polymer (and monomer) comprised the continuous particle‐phase with small internal resinous island domains was observed. A portion of the monomer concentration was again found to be solubilized within the resin domains, yet in this case newly formed initiator radicals encountered a viscous environment instead of an effective barrier. Rate was found to be limited by the feed of monomer to local polymerization in the continuous particle phase from those resinous islands where residual monomer is solubilized. This is what led to continued polymerization, but at a considerably lesser rate. †This paper is dedicated to Professor Gary W. Poehlein, colleague, mentor and friend.

A Column Design for Reducing Viscous Fingering in Size Exclusion Chromatography

Under high concentration overload conditions, resolution during size exclusion chromatography of proteins can be compromised due to nonuniform flow caused by the viscous fingering flow instability. In this work, the nonuniform flow under these chromatographic conditions is analyzed by numerical simulation and magnetic resonance imaging. On the basis of an improved understanding of the flow phenomena, a new column design is proposed. The effectiveness of the design is evaluated by chromatography, magnetic resonance imaging, and numerical simulation.

Design and analysis of the homogeneous and heterogeneous distribution of water confined within colloidal polymer particles

Water is known to distribute within polymeric films in multiple states differentiable by the energy of association. Potentiometric swelling of carboxylated latex samples and subsequent differential scanning calorimetry (DSC) and thermogravimetric analysis verified this distribution of water, specifically confined within colloidal nanoparticle dimensions. DSC cooling curves can delineate between the freezable bound and freezable unbound water at low total water content but become difficult to distinguish the freezable bound contribution at high total water content. Of note is that the ratio of weakly bound water in the secondary layer to the water strongly hydrogen-bound to the polymer is approximately constant regardless of carboxylic acid type and, in fact, is greater for the case of the hydrophobic base polymer. Aside from its distribution within the particles, the total water content also appeared to be more related to the hydroplasticized glass point of the polymer colloid as opposed to the polarity of the polymer.

Selective Detection of Lysozyme Biomarker Utilizing Large Area Chemical Vapor Deposition-Grown Graphene-Based Field-Effect Transistor

Selective and rapid detection of biomarkers is of utmost importance in modern day health care for early stage diagnosis to prevent fatal diseases and infections. Among several protein biomarkers, the role of lysozyme has been found to be especially important in human immune system to prevent several bacterial infections and other chronic disease such as bronchopulmonary dysplasia. Thus, real-time monitoring of lysozyme concentration in a human body can pave a facile route for early warning for potential bacterial infections. Here, we present for the first time a label-free lysozyme protein sensor that is rapid and selective based on a graphene field-effect transistor (GFET) functionalized with selectively designed single-stranded probe DNA (pDNA) with high binding affinity toward lysozyme molecules. When the target lysozyme molecules bind to the surface-immobilized pDNAs, the resulting shift of the charge neutrality points of the GFET device, also known as the Dirac voltage, varied systematically with the concentration of target lysozyme molecules. The experimental results show that the GFET-based biosensor is capable of detecting lysozyme molecules in the concentration range from 10 nM to 1 µM.

A concept for a soft gamma-ray concentrator using thin-film multilayer structures

We are investigating the use of thin-film, multilayer structures to form optics capable of concentrating soft gamma rays with energies greater than 100 keV, beyond the reach of current grazing-incidence hard X-ray mirrors. Alternating layers of low- and high-density materials (e.g., polymers and metals) will channel soft gamma-ray photons via total external reflection. A suitable arrangement of bent structures will then concentrate the incident radiation to a point. Gamma-ray optics made in this way offer the potential for soft gamma-ray telescopes with focal lengths of less than 10 m, removing the need for formation flying spacecraft and opening the field up to balloon-borne instruments. Following initial investigations conducted at Los Alamos National Laboratory, we have constructed and tested a prototype structure using spin coating combined with magnetron sputtering. We are now investigating whether it is possible to grow such flexible multi-layer structures with the required thicknesses and smoothness more quickly by using magnetron sputter and pulsed laser deposition techniques. We present the latest results of our fabrication and gamma-ray channeling tests, and describe our modeling of the sensitivity of potential concentrator-based telescope designs. If successful, this technology offers the potential for transformational increases in sensitivity while dramatically improving the system-level performance of future high-energy astronomy missions through reduced mass and complexity.

A soft gamma-ray concentrator using thin-film multilayer structures

We have begun to investigate the use of thin-film, multilayer structures to form optics capable of concentrating soft gamma rays with energies greater than 100 keV, beyond the reach of current grazing-incidence hard X-ray mirrors. Alternating layers of low- and high-density materials (e.g., polymers and metals) will channel soft gamma-ray photons via total external reflection. A suitable arrangement of bent structures will then concentrate the incident radiation to a point. Gamma-ray optics made in this way offer the potential for soft gamma-ray telescopes with focal lengths of less than 10 m, removing the need for formation flying spacecraft and opening the field up to balloon-borne instruments. Building on initial investigations at Los Alamos National Laboratory, we are investigating whether it is possible to grow such flexible multi-layer structures with the required thicknesses and smoothness using magnetron sputter and pulsed laser deposition techniques. We present the initial results of tests aimed at fabricating such structures by combining magnetron sputtering with either spin coating or pulsed laser deposition, and demonstrating gamma-ray channeling of 122 keV photons in the laboratory. If successful, this technology offers the potential for transformational increases in sensitivity while dramatically improving the system-level performance of future high-energy astronomy missions through reduced mass and complexity.