59 research outputs found
Mixed micelles system: equilibrium and kinetics
Lipid-detergent systems are interesting to study, as the two
amphiphiles have very different spontaneous curvature, however
readily form mixed micelles in solution. These micelles can be shorter
cylindrical micelles or long worm-like micelles. For such a system
the size of the micelles varies strongly with solute conditions,
being dependent on the total amount of amphiphile in solution, as
well as, the lipid to detergent ratio in the micelles.
Although the broad phase behaviour of such systems has been studied
and is relatively well understood, there are still many open questions
remaining. Some of the questions that motivated the work presented
are: how the length and composition of the micelles varies within the
micellar region, and how the micelles grow?
The biologically interesting system under study is lecithin and bile salt, where the
equilibrium sizes were experimentally determined for different samples within the
micellar region. A model, combining the length of the micelles, with the
concentrations of lecithin and bile salt in the system is presented,
and is used to calculate the composition of the micelles at
equilibrium.
The kinetics of the growth of the micelles after a pertubation
causing a shift in the equilibrium size has not been studied in
detail before. The kinetics of the system are studied using a
stopped flow setup, which I
specifically designed for neutron scattering experiments. The
stopped flow setup allows for the measurement to start 200ms after the
initial mixing of the two liquids, after dilution of a solution
the micelles relax to a new longer length. The kinetics of this
relaxation
were studied as a function of the initial and final size of the
micelles, as well as, the ionic strength of the solution.
The micelles were found to grow through coalescence, where the rate of
growth seems to be constant for different sizes of micelles and the time
taken for the relaxation depends on the difference between the final
and initial lengths of the micelles. The rate of growth is
strongly influenced through changing the ionic strength of the
solution, indicating the importance of an electrostatic barrier to
the fusion of micelles
Soft Matter Drainage in a rising foam
International audienceRising foams created by continuously blowing gas into a surfactant solution are widely used in many technical processes, such as flotation. The prediction of the liquid fraction profile in such flowing foams is of particular importance since this parameter controls the stability and the rheol-ogy of the final product. Using drift flux analysis and recently developed semi-empirical expressions for foam permeability and osmotic pressure, we build a model predicting the liquid fraction profile as a function of height. The theoretical profiles are very different if the interfaces are considered as mobile or rigid, but all of our experimental profiles are described by the model with mobile interfaces. Even the systems with dodecanol, which are well known to behave as rigid in forced drainage experiments. This is because in rising foams the liquid fraction profile is fixed by the flux at the bottom of the foam. Here the foam is wet with higher permeability and the interfaces are not in equilibrium. These results demonstrate once again that it is not only the surfactant system that controls the mobility of the interface, but also the hydrodynamic problem under consideration. For example liquid flow through the foam during generation or in forced drainage is intrinsically different
Dual gas and oil dispersions in water: production and stability of foamulsion
International audienceIn this study we have investigated mixtures of oil droplets and gas bubbles and show that the oil can have two very different roles, either suppressing foaming or stabilising the foam. We have foamed emulsions made from two different oils (rapeseed and dodecane). For both oils the requirement for the creation of foamulsions is the presence of surfactant above a certain critical threshold, independent of the concentration of oil present. Although the foamability is comparable, the stability of the foamed emulsions is very different for the two oils studied. Varying a few simple parameters gives access to a wide range of behaviours, indeed three different stability regimes are observed: a regime with rapid collapse (within a few minutes), a regime where the oil has no impact, and a regime of high stability. This last regime occurs at high oil fraction in the emulsion, and the strong slowing down of ageing processes is due to the confinement of packed oil droplets between bubbles. We thus show that a simple system consisting of surfactant, water, oil and gas is very versatile and can be controlled by choosing the appropriate physical chemical parameters
Interface-templated crystal growth in sodium dodecyl sulfate solutions with NaCl
Many ionic surfactants, such as sodium dodecyl sulphate (SDS) crystallize out
of solution if the temperature falls below the crystallization boundary. The
crystallization temperature is impacted by solution properties, and can be
decreased with the addition of salt. We have studied SDS crystallization a t
the liquid/vapor interfaces from solutions at high ionic strength (sodium
chloride). We show that the surfactant crystals at the surface grow from
adsorbed SDS molecules, as evidenced by the preferential orientation of the
crystals identified using grazing incidence X-ray diffraction. We find a unique
timescale f or the crystal growth from the evolution of structure, surface
tension, and visual inspection, which can be controlled through varying the SDS
or NaCl concentrations
One for all, all for one : Reaching for consensus on choosing one generic PROM for all National Clinical Quality Registers in Finland
Posteri; Konferenssi International Consortium for Health Outcome Measurements (ICHOM), ICHOM2023 9.-11.10.2023 Barcelona, Spai
Coarsening transitions of wet liquid foams under microgravity conditions
We report foam coarsening studies which were performed in the International
Space Station (ISS) to suppress drainage due to gravity. Foams and bubbly
liquids with controlled liquid fractions between 15 and 50\% were
investigated to study the transition between bubble growth laws previously
reported near the dry limit and the dilute limit (Ostwald ripening). We determined the coarsening rates; for the
driest foams and the bubbly liquids, they are in close agreement with
theoretical predictions. We observe a sharp cross-over between the respective
laws at a critical value . At liquid fractions beyond this transition,
neighboring bubbles are no longer all in contact, like at a jamming transition.
Remarkably is significantly larger than the random close packing
volume fraction of the bubbles which was determined
independently. We attribute the differences between and
to a weakly adhesive bubble interaction that we have
studied in complementary ground-based experiments
- …