Edgar A. O'Rear

Effect of Sasobit and Aspha-Min on Wettability and Adhesion Between Asphalt Binders and Aggregates

The influence of natural wax in asphalt binders and hot-mix asphalt has been studied for decades, with consideration of both negative and positive effects. Recent advances in warm-mix asphalt (WMA) have spurred interest in the use of commercial waxes such as Sasobit and Asphaltan B as additives in asphalt binders to achieve certain positive effects. Despite a number of previous studies, the effect of Sasobit on wettability and adhesion between asphalt binders and aggregates is not fully understood. Likewise, the effect of water vapor released from Aspha-Min, another WMA additive, at production temperatures is not adequately understood, although such water may negatively influence the behavior of WMA. In the present study, the effect of Sasobit and Aspha-Min on wettability and adhesion was investigated using the surface free energy (SFE) method. Dynamic advancing-wetting contact angles were measured for wettability (coating) and dewetting-receding contact angles were measured to evaluate adhesion. It was observed that Sasobit increases the wettability of asphalt binders over aggregates, as indicated by the change in the spreading coefficient. Conversely, a general trend is that Sasobit reduces the adhesion (free energy of adhesion) between asphalt binders and aggregates. In this study, moisture susceptibility is defined as the amount of spontaneously released free energy due to the breaking of the binder-aggregate bond with water. For PG 64-22, a small or no reduction in moisture susceptibility was observed; for PG 70-28, an increase in moisture susceptibility was observed. In case of the Aspha-Min, the overall SFE results are insignificant.

Accelerated thrombolysis and reperfusion in a canine model of myocardial infarction by liposomal encapsulation of streptokinase

The aim of thrombolytic therapy for acute myocardial infarction with plasminogen activators such as streptokinase is to lyse the coronary thrombus and reestablish blood flow as quickly as possible so that heart tissue loss is minimized and mortality rates are improved. Streptokinase has been encapsulated in large unilamellar phospholipid vesicles and tested in an animal model of acute myocardial infarction. The time required to restore vessel patency has been reduced more than 50% when compared with findings for free streptokinase. The total dosage of streptokinase required was lower, and smaller remnant thrombi were observed with the encapsulated agent. Results from this initial unoptimized study may have significant implications for further reduction in mortality from heart attacks by therapy with plasminogen activators.

Thin polypyrrole films formed on mica and alumina with and without surfactant present: characterization by scanning probe and optical microscopy

Abstract Chemical deposition of electrically conducting polypyrrole (PPy) thin films on mica and alumina was carried out in aqueous solutions with and without surfactant. Examination of film morphology and thickness by atomic force microscopy (AFM) indicated a strong dependence of structure on the method of preparation. Films grown in the absence of surfactant were thicker than 150 nm with wrinkles present, indicating the overcoming of film–substrate adhesion by internal film cohesion. Oxidative polymerization with surfactant allowed reproducible synthesis of very thin films (50 nm thickness) with improved adhesion and suppressed formation of wrinkles. Experimental results are discussed within the context of a Stranski–Krastanov model of film growth. Film thickness and surface fractal dimensions were derived from AFM. Fractal analysis of PPy films on alumina helped discern their presence on the microscopically rough substrate and quantitatively expressed the changes in sample color by surface roughness.

Distributed intraclot thrombolysis: mechanism of accelerated thrombolysis with encapsulated plasminogen activators.

Summary.  Background: The delivery of encapsulated plasminogen activators has demonstrated enhanced thrombolysis in vivo in several models. The mechanism of such improvement has not previously been established. Objectives We explored in vitro the mechanism by which microencapsulation of streptokinase in polymeric microparticles accelerates clot digestion and reduces reperfusion times by as much as an order of magnitude in vivo. Methods: The efficacy of microencapsulated streptokinase (MESK) was directly compared with identical dosages of unencapsulated streptokinase (FREE SK) at three initial pressure drops using clots formed of plasma or whole blood in 0.2‐cm inner diameter glass capillary tubes. Results: MESK demonstrated accelerated flow restoration compared with FREE SK for each condition in plasma (23.8 ± 4.5% faster) and whole blood clots (17.2 ± 9.2% faster). Images collected by light microscopy show sites of thrombolysis internal to the clot only with MESK while the spatial distribution of fluorescently labeled streptokinase by confocal microscopy confirms greater penetration of the encapsulated agent compared with unencapsulated streptokinase. Digestion thus proceeds in three dimensions rather than restricted to a two‐dimensional lysis front. Conclusions: The improved clot penetration with MESK establishes enhanced transport with encapsulation and the concept of distributed intraclot thrombolysis as a basis for the accelerated dissolution observed with encapsulated plasminogen activators in vivo.

Thrombolysis Using Liposomal-Encapsulated Streptokinase: An In Vitro Study

Abstract The clot-lysing ability of streptokinase (SK) was examined using membrane-bound thrombi. Encapsulation of SK in large unilamellar phospholipid vesicles (liposomes) resulted in entrapping approximately 30% of its original activity. Measurements of streptokinase activity for liposomal-encapsulated streptokinase (LESK) indicated little loss of activity or leakage in Tris-buffered saline over a 24-hr period at temperatures of 4 and 23°C. However, incubation of free SK and LESK in platelet-poor plasma (PPP) at 37°C resulted in a decrease of SK activity. The retention of SK activity in LESK was considerably higher than that of unentrapped SK. Clot-dissolving time (CDT) was measured by monitoring the pressure drop during slow filtration in plasma through membrane-bound thrombi. The results indicated that both LESK and free SK were able to activate the fibrinolytic system. Without prior incubation in PPP at 37°C, the CDT of a SK and PPP mixture (SK/PPP) was 10.7 ± 1.9 min (n = 12), while that of a LESK and PPP mixture (LESK/PPP) was 12.4 ± 1.7 min (n = 12). The CDT-detected clot-lysing abilities of both SK and LESK were diminished by incubation in PPP, but to different extents. After 15- and 30-min incubations, the CDT of SK/PPP increased significantly to 15.5 ± 1.5 and 24.1 ± 2.4 min (n = 5, P < 0.05), respectively. In contrast, the CDT of LESK/PPP increased to 13.3 ± 0.8 min (n = 5) after 15 min of incubation and to 16.0 ± 1.1 min (n = 5, P < 0.05) after a 30-min incubation. These results suggest that entrapment of SK in liposomes preserves the thrombolytic potential of the plasminogen activator by limiting its exposure to the components of the plasma.

Evaluation for Warm-Mix Additive-Modified Asphalt Binders Using Spectroscopy Techniques

AbstractThe recent increased interest in “fingerprinting” or identifying commonly used construction materials such as asphalt binders is expected to continue in years to come. To capture the basic fingerprint of asphalt binders, spectroscopy devices can be handy and useful. In particular, this study evaluated the effects of two warm-mix asphalt (WMA) additives, Sasobit and aspha-min, on the chemical compositions of a performance grade binder (PG 64-22). Spectroscopy techniques including Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), and X-ray photo electron spectroscopy (XPS) were used in this study. Mass precipitated asphaltenes and maltenes and straight-run asphalt binder samples were analyzed using these techniques, and test results were compared with the rheological data. The effectiveness of an antistripping agent (ASA), AD-here HP Plus, on a WMA-modified binder was also evaluated. Furthermore, the effects of aging on chemical compositions of the ASA-modified binder...

Moisture absorption and wet-adhesion properties of resin transfer molded (RTM) composites containing elastomer-coated glass fibers

Transient water sorption studies were carried out at constant temperature (45 °C) to assess the hydrolytic stability and wet-adhesion properties of glass fiber/epoxy composites having different sizings. Lower effective diffusivity values correlated with improved overall mechanical performance in relation to the control (unsized) samples, and revealed the importance of changing the surface energy characteristics of glass fibers by using distinctively hydrophobic pure polymers. Admicellar polystyrene and styrene-isoprene coatings formed over the inorganic reinforcement appear to create an interface with much higher resistance to moisture attack than the organosilane/matrix interface in composites with commercial sizing. This fact was corroborated by comparing their effectiveness in property retention, which showed the mechanical property (e.g. ultimate tensile strength, stiffness and interlaminar shear strength) increased with respect to the uncoated composites in the dry state as well as after water saturation. Poor wet-adhesion properties of commercial sizings in humid conditions could perhaps be attributed to higher contents of inert material present in these coatings. Fractography analysis was consistent with the previous observations regarding catastrophic failure in composites without coating, and suggested that interfacial debonding, extensive fiber pullout and matrix crazing were the major contributors to the overall failure mechanism. Failed surfaces of both commercial and elastomer-coated composites also showed areas with fiber pullout, but in this case, matrix residues remained on the fiber surfaces, yielding a much rougher appearance. Good fiber-matrix adhesion, particularly in admicellar-coated composites, was also revealed by the presence of hackles and more tortuous failure paths.

Admicellar Chromatography: Separation and Concentration of Isomers Using Two-Dimensional Solvents

Abstract Immobilized surfactant aggregates at a solid/liquid interface can act as two-dimensional solvents to increase the interfacial concentration of organic compounds selectively. This phenomenon is the basis for a new separation process presented here, admicellar chromatography. The technique offers certain advantages over conventional chromatographic separations. Batch and column separations of isomers of heptanol are used to illustrate the concepts of the process. Equilibrium calculations with single component data are found to give reasonable predictions for the batch separation of the isomers.

Growth and characterization of IV–VI semiconductor heterostructures on (100) BaF2

Abstract Techniques for growing p-PbSe0.78Te0.22/n-Pb1−xSnxSe1−yTey/n-PbSe0.78Te0.22 double heterostructures (x up to 0.2 in the liquid growth solution) on (100) BaF2 substrates by liquid phase epitaxy (LPE) are described. Inclusion-free epilayers and good wipeoffs have been consistently achieved using these techniques. Surface morphology of the epilayers is investigated using Nomarski microscopy and atomic force microscopy (AFM). Fourier transform infrared (FTIR) transmission measurements show optical absorption edge energies vary monotonically with tin content and with temperature at an average rate of 0.41 meV per degree in the temperature range of 300 K to 130 K. Tunable diode lasers (TDLs) fabricated from these structures are expected to span a spectral range of 5–7 μm for x=5% and 6–9 μm for x=12% in this temperature range.

Effectiveness of water-bearing and anti-stripping additives in warm mix asphalt technology

Effects of varying dosages of a water-bearing warm mix asphalt (WMA) additive, Advera®, on a performance grade (PG) binder, PG 64-22, were evaluated. The effectiveness of an amine-based liquid anti-stripping (AS) agent, AD-here® HP Plus, on the Advera®-modified binder was also studied. Furthermore, the effect of reduced oxidative ageing on Advera®-modified binder was investigated. The optimum dosage of Advera® was found to be 6% (by the mass of the binder), which did not alter the base binders PG. A fairly small amount (0.5%) of the AS agent was found to be effective in increasing the fatigue and low temperature resistances of the Advera®-modified binder. A notable reduction in the high PG temperature was observed when the Advera®-modified binder was aged (short term) at 135°C, and this observation is in agreement with the test results of the Advera® mix, which showed excessive rutting and moisture susceptibility. Test data from a rotational viscometer showed no reduction in the viscosity and the production temperature of the Advera® mix thereof, indicating the need of an alternate laboratory test method to simulate the working mechanism of Advera®. The findings of this study are expected to enhance the inventory of rheological database and help in implementing WMA mixes in Oklahoma and elsewhere.