Spacing effects on hydrodynamics of heave plates on offshore structures

The nonlinear viscous flow problem associated with a heaving vertical cylinder with two heave plates in the form of two circular disks attached is solved using a finite difference method. Numerical experiments are carried out to investigate the spanwise length effects on the hydrodynamic properties, such as added mass and damping coefficients. Over a Keulegan–Carpenter (KC) number range from 0.1 to 0.6 at frequency parameter (β=7.869×10⁷), calculations indicate that a KC-dependent critical value of spanwise length L/D_d (L—the distance between the disks, and D_d—the diameter of the disks) exists. A significant influence of L/D_d on the vortex shedding patterns around the disks and the hydrodynamic coefficients is revealed when L/D_d is smaller than the critical value due to strong interaction between vortices of different disks. Beyond that limit, however, both added mass and damping coefficients are shown to be rather stable, indicating the independence of the vortex shedding processes of different disks.     

Viscoelastic behavior of surfactants worm-like micellar solution in the presence of alkanolamide

A study of the phase and rheological behavior of anionic surfactant sodium dodecyl trioxyethylene sulfate (SDES) and nonionic polyoxyethylene sorbitan monooleate (Tween-80) with alkanoyl-N-methylethanolamide (C(12), NMEA-12; and C(16), NMEA-16) in aqueous system is presented. Upon addition of NMEA to the semi-dilute solution of SDES or Tween-80, induces micellar growth leading to the formation of a gel-like highly viscoelastic solution in the maximum viscosity region. These solutions obey the Maxwell model of a viscoelastic fluid. It was observed from rheological measurements that NMEA-16 is more effective than NMEA-12 to induce the micellar growth of surfactants. The relationship between the marked changes in viscosity with surfactant-cosurfactant mixing ratio based on the experimental observations is discussed.     

Viscoelastic micellar solutions in a mixed nonionic fluorinated surfactants system and the effect of oils

Formation and rheological behavior of viscoelastic wormlike micelles in aqueous solution of a mixed system of nonionic fluorinated surfactants, perfluoroalkyl sulfonamide ethoxylate, C8F17SO2N(C3H7)(CH2CH2O)nH (abbreviated as C8F17EOn) was studied. In the water-surfactant binary system C8F17EO20 forms an isotropic micellar solution over wide concentration range (>85 wt %) at 25 degrees C. With successive addition of C8F17EO1 to the aqueous C8F17EO20 solution, viscosity of the solution increases swiftly, and a viscoelastic solution is formed. The oscillatory rheological behavior of the viscoelastic solution can be described by Maxwell model at low-frequency region, which is typical of wormlike micelles. With further addition of C8F17EO1, the viscosity decreases after a maximum and phase separation occurs. Addition of a small amount of fluorinated oils to the wormlike micellar solution disrupts the network structure and decreases the viscosity sharply. It is found that polymeric oil, PFP (F-(C3F6O)nCF2CF2COOH), decreases the viscosity more effectively than the perfluorodecalin (PFD). The difference in the effect of oil on rheological properties is explained in terms of the solubilization site of the oils in the hydrophobic interior of the cylindrical aggregates, and their ability to induce rod-sphere transition.     

Polyol-assisted synthesis of TiO2 nanoparticles in a semi-aqueous solvent

TiO₂ (anatase and rutile) nanoparticles with an average crystallite size of 20-40 nm have been prepared at room temperature by polyol-mediated synthesis technique in a semi-aqueous solvent medium using titanium iso-propoxide as the titanium source, acetone as the oil phase and ethylene glycol as the stabilizer. Phase and microstructure of the resultant materials have been characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Photocatalytic degradation of acetaldehyde using TiO₂ nanoparticles was investigated by gas-chromatography technique.     

Modifying infrared scattering effects of single yeast cells with plasmonic metal mesh

The scattering effects in the infrared (IR) spectra of single, isolated bread yeast cells (Saccharomyces cerevisiae) on a ZnSe substrate and in metal microchannels have been probed by Fourier transform infrared imaging microspectroscopy. Absolute extinction [(3.4±0.6)×10(-7) cm(2) at 3178 cm(-1)], scattering, and absorption cross sections for a single yeast cell and a vibrational absorption spectrum have been determined by comparing it to the scattering properties of single, isolated, latex microspheres (polystyrene, 5.0 μm in diameter) on ZnSe, which are well modeled by the Mie scattering theory. Single yeast cells were then placed into the holes of the IR plasmonic mesh, i.e., metal films with arrays of subwavelength holes, yielding "scatter-free" IR absorption spectra, which have undistorted vibrational lineshapes and a rising generic IR absorption baseline. Absolute extinction, scattering, and absorption spectral profiles were determined for a single, ellipsoidal yeast cell to characterize the interplay of these effects.     

Viscoelastic micellar solutions in nonionic fluorinated surfactant systems

The formation and rheological behavior of a viscoelastic wormlike micellar solution in an aqueous solution of a nonionic fluorinated surfactant, perfluoroalkyl sulfonamide ethoxylate, of structure C8F17SO2N(C3H7)(CH2CH2O)10H was studied. Temperature-induced viscosity growth is observed even at low-surfactant concentration (approximately 1 wt %), and viscosity reaches the maximum at a temperature T(eta)-max. Upon successive increases in the temperature, the viscosity decreases, and ultimately a phase separation occurs. Small-angle X-ray scattering (SAXS) measurements confirm the presence of cylindrical aggregates at low temperature, which undergo continuous one-dimensional growth with increasing temperature, and ultimately, an indication of a slight lamellarlike structural pattern is observed, which probably comes from the formation of micellar joints or branching. Such changes in the microstructure result in a decrease in the viscosity and stress-relaxation time, while the network structure is retained; the trends in the evolution of shear modulus (Go) and relaxation time (tauR) with temperature are in agreement with this. With increased surfactant concentration, the temperature corresponding to the viscosity maximum (T eta-max) in the temperature-viscosity curve shifts to lower values, and the viscosity at temperatures below or around T eta-max increases sharply. A viscoelastic solution with Maxwellian-type dynamic rheological behavior at low-shear frequency is formed, which is typical of entangled wormlike micelles. Rheological parameters, eta(o) and Go, show scaling relationships with the surfactant concentrations with exponents slightly greater than the values predicted by the living-polymer model, but the exponent of tauR is in agreement with the theory. Dynamic light-scattering measurements indicate the presence of fast relaxation modes, associated with micelles, and medium and slow modes, associated with transient networks. The disappearance of the slow mode and the predominance of the medium mode as the temperature increases support the conclusions derived from SAXS and rheometry.     

Formation of Lamellar Silica from Lyotropic Liquid Crystals of Dodecyl Benzene Sulfonic Acid

The formation of lamellar mesostructured silica by a neutral route in dodecylbenzene sulfonic acid (DBSA)/aminoalkoxysilane/water systems was investigated by phase study and Small Angle X‐ray Scattering (SAXS). Initially, two lamellar lyotropic phases are found, one corresponding to the DBSA and other corresponding to the DBSA‐aminoalkoxysilane salt. With the hydrolysis and condensation of siloxane groups, the DBSA‐aminoalkoxysilane lyotropic phase disappears and lamellar silica is formed. The lyotropic phase does not act as a true template but as a source of amphiphilic molecules, hence synthesis takes place via a phase separation mechanism. This synthesis route provides an easy way to prepare amino functionalized lamellar silica.     

Fluorescent sensing of anions with acridinedione based neutral PET chemosensor

Newly synthesised fluorescent chemosensor ADDTU contains the thiourea receptor connected to the acridinedione (ADD) fluorophore via a covalent bond, giving rise to a fluorophore-receptor motif. In this fluorescent chemosensor, the anion recognition takes place at the receptor site which result in the concomitant changes in the photophysical properties of a ADD fluorophore by modulation of photoinduced electron transfer (PET) process. The binding ability of these sensor with the anions F(-), Cl(-), Br(-), I(-), HSO(4)(-), ClO(4)(-), AcO(-), H(2)PO(4)(-) and BF(4)(-) (as their tetrabutylammounium salts) in acetonitrile were investigated using UV-vis, steady state and time-resolved emission techniques. ADDTU system allows for the selective fluorescent sensing of AcO(-), H(2)PO(4)(-) and F(-) over other anions in acetonitrile.