Cholesterol increases the magnetic aligning of bicellar disks from an aqueous mixture of DMPC and DMPE-DTPA with complexed thulium ions

Aqueous mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-diethylenetriamine pentaacetate (DMPE-DTPA) with complexed thulium ions (Tm(3+)), and cholesterol with varying molar ratio were studied at different temperatures in the presence and absence of a magnetic field. For mixtures without cholesterol weakly magnetically alignable small disks, so-called bicelles, are formed at temperatures below the phase transition temperature (5-22 °C), as shown by cryo-transmission electron microscopy (cryo-TEM) and small-angle neutron scattering (SANS). In presence of 16 mol % cholesterol the disk size and the magnetic alignability were larger within the entire temperature range studied (5-40 °C). Cholesterol acts as a spacer between DMPE-DTPA with complexed Tm(3+), allowing these molecules to integrate more frequently into the planar part of the bicelles. Replacing DMPC partially by cholesterol thus lead to an increase in magnetic aligning by a higher amount of the magnetic handles (Tm(3+) complexed to DMPE-DTPA) in the plane and by an increased number of phospholipids in the enlarged bicelles. The magnetic aligning was most pronounced at 5 °C. The temperature-dependent structural changes of the DMPC/cholesterol/DMPE-DTPA/Tm(3+) aqueous mixtures are complex, including the transient appearance of holes in the disks at intermediate temperatures.     

Local film thinning due to concentration gradient of an insoluble surfactant at an interface

The local thinning of a viscous liquid film on a substrate driven by a surface (or interfacial) tension gradient due to a concentration gradient of a monolayer of an insoluble surfactant initially non-uniformly distributed at a liquid interface relevant to chemical engineering, biomedical and other applications is investigated. A simple model is presented for the temporal evolution of the profiles of radial variation in the thickness of a thin liquid film, the effects of gravity and capillarity due to deformation of the interface in slowing down the film thinning process being allowed. As time increases, the surfactant spreads and the radius of its front increases inversely with decrease in the two-third power of the film thickness at the center. The model describes well not only the published experimental results but also those obtained by other authors using numerical simulations of a set of coupled partial differential equations.     

Nonionic block copolymer antifoams

Aqueous dispersions of alkoxylated alcohol block copolymer (BCP) drops are investigated as antifoams. A model aqueous nonionic surfactant solution of Polysorbate 20 and an industrial white water suspension are used as foaming systems. Visual evidence obtained using a two-bubble technique involving a CCD camera coupled with high magnification lenses clearly revealed the role of BCP droplets in the bubble coalescence process. The enhancement of bubble coalescence decreased as the temperature increased from 25 to 60 degrees C, which is due to the corresponding decrease in the rigidity associated with the weak interfacial structure and reduced viscosity of the BCP drops. The antifoaming efficiency measured in the macroscopic recirculation foam column increased with temperature from about 13 to 26 degrees C (attaining a maximum) and decreased as temperature increased further. Oscillatory thermo-rheometric measurements showed a sudden increase in the storage modulus (G') by several orders of magnitude, indicating gel formation initiated at about 13 degrees C and having a maximum at around 26 degrees C for an aqueous solution of the BCP above a critical concentration of around 20 wt %. Results obtained using small-angle X-ray scattering, micro-differential scanning calorimetry, and proton nuclear magnetic resonance confirmed the existence of ordered gel-like structures. Furthermore, macroscopic tests using a sparged air foam column showed a significant increase in antifoaming efficiency when highly hydrophobic particles are embedded in the BCP drops dispersed in water.     

Alternating vorticity bands in a solution of wormlike micelles

We report on structural characterization of vorticity bands formed in a wormlike micellar solution by Rheo--small-angle neutron scattering and video imaging experiments. Below a critical shear stress tau{c} in Newtonian and shear-thinning regime, only a minor flow alignment of the micelles is observed. Above tau{c}, in the shear-thickening regime, alternating transparent and turbid bands are formed. Triggered small-angle neutron scattering shows different anisotropic patterns in both bands indicating strongly aligned structures. By high-speed video imaging, we show that such an alignment of micelles does not correspond to a phase of lower viscosity.     

Synthesis and characterization of colored EUDRAGIT® as enteric coating material

The synthesis of novel polymeric dyes by directly attaching toluidine blue O and MPPD via EDC and CDI coupling is described for polymers with enteric properties [poly(methacrylic acid‐co‐ethyl acrylate)]. The polymeric dyes are analyzed by SEC and UV/Vis measurements as well as investigated regarding their dissolution and permeation characteristics. Almost no changes between the modified and nonmodified polymer could be observed by conventional drug studies and a self‐established method for dissolution rates. Also no influence on the film formation properties was observed by SEM measurements. In vitro toxicity studies showed no increase of toxicity compared to the non modified polymer. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2386–2393     

Rheology of concentrated suspensions containing mixtures of spheres and fibres

Optimising flow properties of concentrated suspensions is an important issue common for many industries. The rheology of concentrated suspensions has therefore been studied intensively both experimentally and theoretically. Most studies have focused on monodisperse and polydisperse suspensions of either spheres or fibres. In practice, most suspensions contain particles that are polydisperse both in size and shape. A mixing rule for such systems is expected to be a powerful tool for engineers and product designers. Therefore in this work, suspensions of spheres, fibres and mixtures thereof were characterised using rotational shear rheometry and in-line image analyses. Thereby, total solids volume concentration and fibre fraction was varied. Results from transient and steady-state shear rheometry are discussed with respect to concentration, fibre fraction, and shear induced microstructure. Experimentally obtained viscosity data were accurately fitted using the model proposed by Farris (T Soc Rheol 12:281, 1968) for mixtures of monodisperse non-interacting spheres of different sizes.Originally presented at the Annual European Rheology Conference 2003, AERC 2003