Micellar size of drag reducing cationic surfactants

 Dynamic light scattering was employed to determine the effects of surfactant nature, concentration and counterion ratios, and shear on the hydrodynamic radii of micelles of commercial cationic surfactants which are powerful drag reducers in turbulent flow at high temperatures. Such surfactants are potentially useful for reducing pumping energy losses in district heating and cooling systems. Received: 22 January 1996 Accepted: 29 August 1996     

Turbulence measurements of drag reducing surfactant systems

LDA measurements were made of mean velocity and of turbulence intensity in a 39.4mm diameter tube, the first measurements in three directions on drag reducing surfactant solutions (0.05% and 0.1% Habon G). Drag reduction exceeded the predictions of the Virk maximum drag reduction asymptote and elastic sublayer mean velocity profiles are steeper than the profile proposed by Virk for maximum drag reducing asymptote solutions. Axial turbulence intensities for Habon G solutions are higher than those for water near the wall, lower in most of the outer region and about the same at the center. Tangential and radial turbulence intensities are lower than those for water.     

Comparison of oleyl and elaidyl isomer surfactant-counterion systems in drag reduction, rheological properties and nanostructure

Compared with quaternary ammonium cationic surfactants with saturated alkyl chains, quaternary ammonium cationic surfactants with one double-bond in their alkyl chains, when mixed with appropriate counterions (in certain molar concentration ratios, ξ), can reach much lower effective drag-reduction temperatures, while maintaining the upper drag-reduction temperature limit of the corresponding saturated drag reducing surfactant solutions. No previous study has compared the effects of cis- vs. trans-unsaturated alkyl hydrocarbon tail configurations (oleyl vs. elaidyl) trimethyl ammonium chloride cationic surfactants at different counterion/surfactant concentration ratios on micellar nanostructures, (1)H NMR spectra and on rheological and drag-reduction behavior of their solutions. Since neither pure oleyl (cis-) nor elaidyl (trans-) trimethyl ammonium chloride surfactants are commercially available, they were synthesized and their 5mM solutions with NaSal counterion at concentrations of 5mM, 7.5mM and 12.5mM were studied.     

EPR study of oriented photoexcited triplets of porphyrins and chlorophylls in a liquid crystal

An EPR study of the photoexcited triplet state of porphyrins, Chl a and the covalently linked dimer of Zn pyrochlorophyllide a, in a liquid crystal, is reported The metalloporphyrins interact to form excimers The low intramolecular energy transfer rate in the dimer (? 10⁶s^?1) suggests that the unfolded form predominates.     

Effect of variations in counterion to surfactant ratio on rheology and microstructures of drag reducing cationic surfactant systems

Rheology, drag reduction and cryo-TEM experiments were performed on Arquad 16–50/NaSal and Ethoquad O/12/NaSal surfactant systems at different counterion-to-surfactant ratios and at constant low surfactant concentrations, 5 mM, appropriate for drag reduction. The molar ratio of counterion-to-surface was varied from 0.6 to 2.5. All the surfactant systems described here are viscoelastic and drag reducing. The viscoelasticity and drag reducing effectiveness increase with increase in counterion/surfactant ratio. Network are present in the solutions with high ratio, and they are viscoelastic. However, shear is needed to induce network formation for solutions at low ratio. Cryo-TEM images confirm the existence of thread-like micelles which form entanglement networks, and show that the micellar network becomes denser with increasing counterion/surfactant ratio in one surfactant series. Both increase in the counterion/surfactant ratio and increase in the shear rate result in shorter relaxation times. For some of these systems, abrupt increase in viscosity is observed at certain shear rates which are time effects affecting microstructure rearrangements rather than formation of shear induced structures.     

A photoactivable probe for calcium binding proteins

Ca2+ as a signaling molecule carries information pivotal to cell life and death via its reversible interaction with a specific site in a protein. Although numerous Ca2+-dependent activities are known, the proteins responsible for some of these activities remain unidentified. We synthesized and characterized a photoreactive reagent, azido ruthenium (AzRu), which interacts specifically with Ca2+ binding proteins and strongly inhibits their Ca2+-dependent activities, regardless of their catalytic mechanisms or functional state as purified proteins, embedded in the membrane or in intact cells. As expected from a Ca2+ binding protein-specific reagent, AzRu had no effect on Ca2+-independent and Mg2+-dependent activities. Az103Ru covalently bound, and specifically labeled, known Ca2+ binding proteins. AzRu is a photoreactive reagent that provides an approach for identification of Ca2+ binding proteins, characterization of their binding sites, and exploration of new Ca2+-dependent processes.     

Heat Transfer Enhancement for Drag-Reducing Surfactant Fluid Using Photo-Rheological Counterion

A new heat transfer enhancement method for a drag-reducing surfactant solution using a photo-rheological counterion was discussed. Surfactant and counterion concentration effect on heat transfer enhancement was investigated combining with rheological test. Surfactant/counterion concentration of 4 mM/5 mM was considered as an efficient concentration for heat transfer enhancement.     

Co-solvent effects on drag reduction, rheological properties and micelle microstructures of cationic surfactants

Some quaternary cationic surfactants, when mixed with a counterion, are known to self-assemble into threadlike micelles in water. Such behavior causes drastic changes in rheological properties of even very dilute solutions, allowing them to be used as drag reducing agents (DRA) in turbulent pipe flow circulating systems, such as district cooling/heating systems. Surfactant self-assembly is a physicochemical phenomenon whose character depends on surfactant nature and concentration, nature of the solvent, temperature and type and concentration of counterions. This study investigates drag reduction (DR) and rheological properties of two cationic surfactants, Ethoquad O/12 (oleyl bis(hydroxyethyl)methylammonium chloride) and Ethoquad O/13 (oleyl tris(hydroxyethyl) ammonium acetate), with excess salicylate counterion (NaSal), in mixed solvents containing 0 to 28 wt% ethylene glycol (EG) and water. The addition of EG to the solvent had greater effects on solutions' DR ability, shear viscosity, apparent extensional viscosity and viscoelasticity at 25 degrees C than at approximately 0 degrees C. Cryo-TEM images show threadlike micelle in these systems. DR at low temperatures in solutions containing moderate amount of EG can be utilized in a new approach to energy saving in district cooling systems using EG-water based mixtures as the cooling fluids.     

In vivo damage to chorioallantoic membrane blood vessels by porphycene-induced photodynamic therapy

Photodynamic therapy (PDT) was performed in the chick embryo chorioallantoic membrane (CAM) for the purpose of quantitative evaluation of several porphycenes as potential photosensitizers. Porphycenes are structural isomers of porphine possessing lower symmetry of the macrocycle and are characterized by 10-fold higher absorption at the therapeutic wavelengths for PDT (λ > 630 nm). PDT-induced damage to CAM blood vessels included vasoconstriction and blanching, as was monitored during irradiation and videotaped. Image analysis techniques enabled us to follow PDT-induced constriction of vessel diameter (to 50%), reduction of blood perfusion (to 40% lower optical density) and shrinkage of implanted tumours (to 10% of their original area). The observed PDT efficacy of functionalized porphycenes is positively correlated with the number of polar substituents.