Biomedical subjects

JF Scamehorn

Publications and source records attributed to JF Scamehorn.

3 recordsLinked to original sources

PubMed1999

Directional Converter Arm Method for Surface and Interfacial Tension Measurements with a Top-Loading Balance.

A method is described for utilizing a top-loading balance, with a directional converter arm, in vertical-pull surface force measurements. The Padday rod-pull technique, the du Noüy ring method, and the Wilhelmy plate method are utilized with rods, thin-walled tubes, wire rings, and plates either rigidly attached to the converter arm or hanging freely from a hook at the end of the arm. The robustness, large weighing capacity, and accuracy of top-loading balances make them ideally suited for a variety of types of surface and interfacial tension measurements. The converter arm method can be used with a stainless steel rod (3-7 mm in diameter) in vertical-pull surface tension measurements, with samples having volumes of only a few tenths of a milliliter. Measurements on very small liquid volumes are feasible because the rod is firmly attached to the converter arm rather than hanging freely as in measurements with balances mounted above the sample; therefore, the rod cannot swing toward and attach to the wall of small sample tubes. Automation of force and height measurements with the converter arm/top-loading balance method is straightforward. Copyright 1999 Academic Press.

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PubMed1999

Use of Micellar-Enhanced Ultrafiltration at Low Surfactant Concentrations and with Anionic-Nonionic Surfactant Mixtures.

Micellar-enhanced ultrafiltration is a separation technique which can be used to remove metal ions or dissolved organics from water. Metal ions bind to the surface of negatively charged micelles of an anionic surfactant while organic solutes tend to dissolve or solubilized within the micelles. The mixture is then forced through an ultrafiltration membrane with pore sizes small enough to block passage of the micelles and associated metal ions and/or dissolved organics. Monomeric or unassociated surfactant passes through the membrane and does not contribute to the separation. This paper considers advantages of addition of small concentrations of nonionic surfactant to an anionic surfactant; the resulting anionic-nonionic mixed micelles exhibit negative deviation from ideality of mixing which leads to a smaller fraction of the surfactant being present as monomer and a subsequently larger fraction present in the micellar form. The addition of nonionic surfactant improved the separation of divalent zinc substantially at total concentrations above the critical micelle concentration (cmc) of the anionic surfactant. Both zinc and tert-butylphenol (a nonionic organic solute) show unexpected rejection at surfactant concentrations moderately below the cmc, where micelles are absent. This is considered as due to a higher surfactant concentration in the gel layer adjacent to the membrane where micelles are present. Reduction of this rejection at lower transmembrane pressure drops supports this mechanism. Some rejection of zinc was observed in the absence of surfactant but not of tert-butylphenol, indicating an additional effect of membrane charge for ionic solutes. Copyright 1999 Academic Press.

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PubMed1997

Volumetric Mixing in Anionic/Nonionic, Cationic/Nonionic, and Anionic/Cationic Mixed Micelles

The volumetric mixing in anionic/nonionic, cationic/nonionic, and anionic/cationic mixed micelles was determined by examining the total surfactant apparent molar volumes (phiV,tot) at total surfactant concentrations (CT) much greater than the mixture critical micelle concentration (CMCm). The mixed surfactant systems investigated were sodium dodecyl sulfate and a polyethoxylated nonylphenol, at 0.15 M NaCl and with no added NaCl; cetyl pyridinium chloride and polyethoxylated nonylphenol, at 0.03 M NaCl; and sodium dodecyl sulfate and dodecyl pyridinium chloride, at 0.15 M NaCl. For all of the mixed surfactant systems investigated, the volumetric mixing in the mixed micelles at CT >> CMCm was ideal, even though the free energies of mixing at the onset of mixed micelle formation (as indicated by the mixture critical micelle concentrations at CT = CMCm) exhibited strong negative deviations from ideality. Furthermore, added electrolyte was shown to have virtually no effect on the phiV,tot data (nor, consequently, the volumetric mixing) for the anionic/nonionic mixed surfactant system. The results of this study suggest that at CT >> CMCm, the electrostatic interactions do not significantly affect the molar volume of the mixed micelle. Therefore, the micelle hydrophobic core dominates the volumetric mixing in mixed micelles at CT >> CMCm.

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