17 research outputs found
Influence of Ibuprofen on Phospholipid Membranes
Basic understanding of biological membranes is of paramount importance as
these membranes comprise the very building blocks of life itself. Cells depend
in their function on a range of properties of the membrane, which are important
for the stability and function of the cell, information and nutrient transport,
waste disposal and finally the admission of drugs into the cell and also the
deflection of bacteria and viruses.
We have investigated the influence of ibuprofen on the structure and dynamics
of L-alpha-phosphatidylcholine (SoyPC) membranes by means of grazing incidence
small-angle neutron scattering (GISANS), neutron reflectometry and grazing
incidence neutron spin echo spectroscopy (GINSES). From the results of these
experiments we were able to determine that ibuprofen induces a two-step
structuring behavior in the SoyPC films, where the structure evolves from the
purely lamellar phase for pure SoyPC over a superposition of two hexagonal
phases to a purely hexago- nal phase at high concentrations. Additionally,
introduction of ibuprofen stiffens the membranes. This behavior may be
instrumental in explaining the toxic behavior of ibuprofen in long-term
application.Comment: -Improved indexing in Fig. 4e) -changed concentrations to mol%
-improved arguments, however conclusions stay unchange
Exploring Hidden Local Ordering in Microemulsions with a Weak Directive Second Order Parameter
So far, the near-surface ordering of microemulsions was focused on lamellar ordering while the bulk microemulsion was bicontinuous. In a series of different non-ionic surfactants the near-surface ordering of microemulsions at a hydrophilic silicon surface was studied using grazing incidence small angle neutron scattering. For the surfactant C8E3, most likely a gyroid structure was found at the solid–liquid interface, while the more efficient surfactants find lamellar ordering up to lamellar capillary condensation. The ranges for near-surface ordering are deeper than the bulk correlation lengths. These findings point towards theories that use directional order parameters that would lead to deeper near-surface ordering than simple theories with a single scalar order parameter would predict. Rheology experiments display high viscosities at very low shear rates and, therefore, support the existence of a directional order parameter
Stability of near-surface ordering of bicontinuous microemulsions in external shear-fields
The lubrication effect of bicontinuous microemulsions describes a facilitated flow along hydrophilic planar surfaces because the fluid forms lamellar domains that can slide off along each other much better than randomly ordered domains. The applicability of this effect is based on the prerequisite of the lamellar structure not being destroyed by external shear-fields. In this paper, we demonstrate that the lamellar structure is highly stable for shear rates of up to 600 s−1 using neutron reflectivity and grazing incidence small angle neutron scattering experiments. The transition structure that consists of perforated lamellae is attacked by the flow, and the bicontinuous microemulsion comes closer to the solid interface when shear is applied. All of this verifies the stability of the lubrication effect for technical applications
Polymer enrichment decelerates surfactant membranes near interfaces
Close to a planar surface, lamellar structures are imposed upon otherwise bulk bicontinuous microemulsions. Thermally induced membrane undulations are modified by the presence of the rigid interface. While it has been shown that a pure membrane's dynamics are accelerated close to the interface, we observed nearly unchanged relaxation rates for membranes spiked with large amphiphilic diblock copolymers. An increase of the polymer concentration by a factor of 2–3 for the first and second surfactant membrane layers was observed. We interpret the reduced relaxation times as the result of an interplay between the bending rigidity and the characteristic distance of the first surfactant membrane to the rigid interface, which causes the hydrodynamic and steric interface effects described in Seifert's theory. The influence of these effects on decorated membranes yields a reduction of the frequencies and an amplification of the amplitudes of long-wavelength undulations, which are in accordance to our experimental finding
Dynamics of polymeric additives in bicontinuous microemulsions adjacent to planar hydrophilic surfaces
Close to a planar surface, lamellar structures are imposed upon otherwise bulk bicontinuous microemulsions. Thermally induced membrane undulations are modified by the presence of the rigid interface. While it has been shown that pure membrane dynamics are accelerated close to the interface, we observed nearly unchanged relaxation rates for membranes spiked with large amphiphilic diblock copolymers with respect to the bulk. An increase of the polymer concentration by a factor of 2–3 for the first and second surfactant membrane layers was observed. We interpret the reduced relaxation times as the result of an interplay between the bending rigidity and the characteristic distance of the first surfactant membrane to the rigid interface, which causes the hydrodynamic and steric interface effects described in Seifert’s theory. The influence of these effects on decorated membranes yields a reduction of the frequencies and an amplification of the amplitudes of long-wavelength undulations, which are in accordance to our experimental findings