Characterization of foam flowing in a granular medium in the presence of oil by small angle neutron scattering

Probing foams from the nanometer to the millimeter scale by coupling small-angle neutron scattering, imaging, and electrical conductivity measurements

Liquid foams are multi-scale structures whose structural characterization requires the combination of very different techniques. This inherently complex task is made more difficult by the fact that foams are also intrinsically unstable systems and that their properties are highly dependent on the production protocol and sample container. To tackle these issues, a new device has been developed that enables the simultaneous time-resolved investigation of foams by small-angle neutron scattering (SANS), electrical conductivity, and bubbles imaging. This device allows the characterization of the foam and its aging from nanometer up to centimeter scale in a single experiment. A specific SANS model was developed to quantitatively adjust the scattering intensity from the dry foam. Structural features such as the liquid fraction, specific surface area of the Plateau borders and inter-bubble films, and thin film thickness were deduced from this analysis, and some of these values were compared with values extracted from the other applied techniques. This approach has been applied to a surfactant-stabilized liquid foam under free drainage and the underlying foam destabilization mechanisms were discussed with unprecedented detail. For example, the information extracted from the image analysis and SANS data allows for the first time to determine the disjoining pressure vs. thickness isotherm in a real, draining foam.

A Modiied 3-Way Tap to Enhance the Stability and Uniformity of Sclerosant Foam

BACKGROUND

The Tessari method, mixing air with the sclerosant through a 3-way tap and 2 syringes, is the most widely used method to prepare foam in foam sclerotherapy. Uniform foam with smaller bubbles has great clinical significance for venous insufficiency. We aim to modify the traditional 3-way tap to produce more uniform and stable foam with smaller bubbles.

METHODS

The traditional 3-way tap was modified by inserting a porous film within its channel.

EXPERIMENT DESIGN

the foam was prepared with 2 mL polidocanol plus 8 mL air plus 0.05 mL hyaluronic acid; group 1, foam prepared with 20 quick passes through a traditional 3-way tap; and groups 2-7, foam prepared using the modified 3-way tap, with 10, 12, 14, 16, 18, and 20 quick passes, respectively. The uniformity of the foam was observed under optical microscopy, and the size of bubbles quantified using the Nano measurement software. The stability of the foam was evaluated using the foam half-life time.

RESULTS

The foam half-life times of groups 1-7 were 306.4, 257.4, 285.6, 304.4, 318.6, 330.2, 331.3 sec, respectively. The modified tap also produced a more uniform distribution of smaller bubbles (group 7) compared with traditional tap (group 1).

CONCLUSIONS

Modified 3-way tap enhanced the stability of the sclerosant foam, with a more uniform distribution of smaller bubbles.

Foam trapping in a 3D porous medium: in situ observations by ultra-fast X-ray microtomography

One of the challenges in the study of foam transport in 3D porous media is to have an adequate spatial and temporal resolution to get a better understanding of the local phenomenon at the pore scale in a non-destructive way. We present an experimental study in which ultra-fast X-ray microtomography is used to investigate the foam trapping while the foam is flowing in a 3D porous medium. Preformed aqueous foam is injected into a rotating cell containing a 3D granular medium made of silica grains. The use of rotating seals allows the cell to rotate continuously at a rate of one revolution per second, compatible with the fast X-ray tomography at SOLEIL synchrotron. We visualize the foam flow and track the trapping of bubbles with an acquisition time of about one second and a spatial resolution of a few microns (pixel size of one micron). This allows us to extract the characteristics and reliable statistics about trapped bubbles inside the granular medium and to observe their local behavior. With this setup and technique we obtain access to the dynamics of foam trapping during the flow and the texture variations of the foam in the trapped zones. These local trapping events are well correlated with the macroscopical measurement of the pressure gradient over the cell.