Biomedical subjects

J Giermanska-Kahn

Publications and source records attributed to J Giermanska-Kahn.

4 recordsLinked to original sources

PubMed2005

Particle-stabilized emulsions comprised of solid droplets.

We kinetically stabilize oil-in-water emulsions comprising paraffin crystals by adsorbing solid particles (silica) of colloidal size at the oil/water interface. We obtain a set of emulsions that are quiescently stable for a long period of time (months), while the same emulsions are destabilized after only a few hours in the presence of surfactant molecules alone. The emulsions are submitted to a shear stress in order to probe their stability under flow conditions. Partial coalescence and gelation occur when the shear is applied for a sufficiently long period of time. The experiments reveal the existence of a critical droplet mass fraction, phi*, that defines a sharp transition between slow and fast gelation. The process of gelation is rather slow for phi < phi*, occurring at the scale of hours, and becomes almost instantaneous above phi*.

Journal Article↗

PubMed2002

Double emulsions: how does release occur?

Water-in-oil-in-water double emulsions (W/O/W) consist of dispersed oil globules containing smaller aqueous droplets. These materials offer interesting possibilities for the controlled release of chemical species initially entrapped in the internal droplets. A better understanding of the stability conditions and release properties in double emulsions requires the use of model systems with a well-defined droplet size. In this paper, we use quasi-monodisperse double emulsions made of calibrated water droplets and oil globules to investigate the two mechanisms that are responsible for the release of a chemical substance (NaCl). (i) One is due to the coalescence of the thin liquid film separating the internal droplets and the globule surfaces. (ii) The other mechanism termed as 'compositional ripening' occurs without film rupturing; instead it occurs by diffusion and/or permeation of the chemical substance across the oil phase. By varying the proportions and/or the chemical nature of the surface active species it is possible to shift from one mechanism to the other one. We therefore study separately both mechanisms and we establish some basic rules that govern the behavior of W/O/W double emulsions.

Biopolymers↗

PubMed2001

Double emulsions: a tool for probing thin-film metastability.

We study the kinetics of the release of monodisperse water-in-oil-in-water double emulsions in the regime dominated by coalescence of the internal aqueous droplets onto the globule interface. By measuring the rate of release of adsorbed droplets, we directly determine the average lifetime of the thin film that forms between the small internal droplets and the globule surface. Therefore, the activation energy and the natural frequency of the hole nucleation process within the adhesive thin liquid films are unambiguously deduced.

Journal Article↗

PubMed1999

Negative effective surface viscosities in insoluble fatty acid monolayers: effect of phase transitions on dilational viscoelasticity.

The viscoelastic properties of insoluble monolayers have been investigated by the excited electrocapillary waves method. Effective negative values of dilational viscosities have been obtained in the liquid expanded and liquid condensed phases of insoluble monolayers of myristic, pentadecanoic, and stearic acids. However, the surface viscosity remains positive for the more expanded monolayers of ethyl palmitate ester. Possible origins of such a behavior are discussed in terms of transitional effects between the two-dimensional coexisting phases.

Journal Article↗