The European Physical Journal E

The impact of selected metallophthalocyanines, featuring diverse molecular structure, upon the fluidity of liposome membranes was studied using the spin label EPR technique. The “mono”-type MPc's (M = Zn, Sn; Pc = C32H16N8 is the phthalocyanine ligand) and sandwich LnPc2 complexes (Ln = Nd, Sm, Gd) were explored. Liposomes were obtained in a sonication process, from egg yolk lecithin (EYL) in water. TEMPO and 16-DOXYL spin labels were used to monitor the peripheral and central part of the lipid double layer, respectively, which allowed to localize the phthalocyanine additive within the bilayer, as well as to perform independent measurements of changes in fluidity upon addition thereof. All the complexes tested were found to increase the fluidity in the middle of the lipid bilayer. However, at the water-lipid interface the LnPc2 compounds showed a relative small effect upon the phospholipids' arrangement, whereas in the case of ZnPc and SnPc it was found much more pronounced. EPR results were supplemented by measurements of static electrical charge, the investigated phthalocyanines may potentially feed into the membrane thus affecting its stability.

Inhomogeneous deformations are observed in stretched natural rubber of different crosslink density; the conditions of observation, nucleation and propagation are given in the first part of the paper. In samples of low crosslink density these inhomogeneities recall necking observed in others materials and in glassy polymers when the materials are drawn above a critical draw ratio. The difference is that in natural rubbers, NR, they nucleate and propagate at constant stress during unloading. This phenomenon, called inverse yielding appears during recovery only if the samples have been drawn previously in the hardening domain. During necking propagation the stress is constant. The mechanical and crystallinity properties of samples with and without inverse yielding are studied as a function of draw ratio, crosslink density and temperature. In the second part of the paper this transition zone (neck) of thickness 2 mm is studied by WAXS at the synchrotron source. From the orientation of NR crystallites and from the orientation of the stearic acid (2%, present in this type of rubber) we conclude that the deformation in the neck follows the flow lines. From the local crystallinity of the NR crystallites one deduces the local draw ratio across this transition zone. We suggest that in all these rubbers, which present a plateau of the recovery stress strain curve, micronecking exists. This effect is discussed in the framework of the Flory theory.-1

The shape as well as tension and pressure inside an uncharged vesicle are understood to be determined by the reduced volume of a vesicle. These parameters are important for a vesicle or a biological cell, since they can affect bio-physical processes such as osmosis and permeation, interaction with external agents such as bio-macromolecules as well as thermal fluctuations in a bilayer membrane of a vesicle. Charged membranes are ubiquitous in nature, most biological cell bio-membranes are charged, and therefore the knowledge of shape, tension and pressure of charged vesicles is critical. Additionally, the distribution of charges in the inner and outer leaflets is also important as it can affect the spatial interaction of a bilayer membrane with proteins and other micro and macromolecular species. This work addresses these issues in the low-charge and low-curvature limit. Our analysis indicates that despite a very strong two-way coupling between the charge and the curvature, the shapes of charged vesicles remain similar to that of uncharged vesicles at comparable reduced volumes, even for reasonable values of total charge. However, the tension and pressure values are higher, and are accurately estimated in our analysis. The charge distribution on the outer and inner leaflet which is strongly affected by the curvature is calculated. The value of spontaneous curvature due to charge redistribution is also estimated. The insensitivity of the shape to charges persists even when only the outer leaflet is charged instead of charged inner and outer leaflets.

When a microparticle is trapped at a fluid interface, particle’s electrical charge and weight combine to deform the interface. Such deformation is expected to affect the particle diffusion via hydrodynamics boundary conditions. Using available models of particle-induced electrostatic deformation of the interface and particle dynamics at the interface, we are able to analytically predict particle diffusion coefficient values in a large range of particle’s contact angle and size. This might offer a solid background of numerical values to compare with for future experimental studies in the field of particle diffusion at a fluid interface.

The aim of the paper is to study the deviation of magnetic properties of the magnetic fluids prepared for this study, from ideal (Langevin) behaviour, i.e. to estimate particle interaction influence and dimensions and influence of particle aggregates, as well as to explain the related effects observed. We also determine the particle coupling parameter, the particle nonmagnetic layer thickness, and the particle distribution, which are fundamental for sample characterization. A comparison of the studied magnetic fluids with each other, with respect to microstructure formation and particle interaction strength is finally done. For these purposes, a concentration dependence study, following the proposed “dilution series approach”, is performed. Three series of dilutions of three types of magnetic fluids were prepared and analyzed.