Eric Tyrode

Surfactant-oil-water systems near the affinity inversion. XII. Emulsion drop size versus formulation and composition

ABSTRACT Emulsion drop size depends on the both formulation and composition of the surfactant-oil-water system, as well as on the stirring conditions prevailing during emulsification. General trends versus formulation or composition changes are presented. However, it is shown that the effects are not independent and that a proper combination of these parameters allows the attainment of very small drop size, even at low stirring energy. An overall phenomenology is presented on a two-dimensional formulation-composition map from which it is easy to select the best emulsification conditions.

Foamability and foam stability at high pressures and temperatures. I. Instrument validation

An instrument was designed and assembled with the aim of measuring macroscopic properties of foams (such as foamability and stability) under high pressures and moderate temperatures (up to 105 bar and 425 K, respectively). The device makes use of infrared sensors to detect the foam forefront position as it is generated by gas sparging in the foaming solution. The measurement makes use of a modified dynamic Bikerman protocol to estimate the foamability and stability of the studied solution. Traditional direct observation used in foam experiments at ambient conditions is therefore circumvented and the instrument can be set up in an appropriate place and monitored remotely so as to reduce the risks involved in high-pressure, high-temperature operations. Data from the infrared system allows not only following the dynamics of foam phenomena but also the relative foam quality along the column, and the presence of air pockets in the case of unstable or pulsating foams. A series of fluorosurfactants (cationic, anionic, and nonionic) were used to validate the instrument and the effect of temperature on foamability, foam stability and foam quality is discussed. Finally, synergistic effects were observed with respect to the foam behavior of different mixtures of the studied surfactants.

Temperature-Dependent Deicing Properties of Electrostatically Anchored Branched Brush Layers of Poly(ethylene oxide)

The hydration water of hydrophilic polymers freezes at subzero temperatures. The adsorption of such polymers will result in a hydrophilic surface layer that strongly binds water. Provided this interfacial hydration water remains liquidlike at subzero temperatures, its presence could possibly reduce ice adhesion, in particular, if the liquidlike layer is thicker than or comparable to the surface roughness. To explore this idea, a diblock copolymer, having one branched bottle-brush block of poly(ethylene oxide) and one linear cationic block, was electrostatically anchored on flat silica surfaces. The shear ice adhesion strength on such polymer-coated surfaces was investigated down to -25 °C using a homebuilt device. In addition, the temperature dependence of the ice adhesion on surfaces coated with only the cationic block, only the branched bottle-brush block, and with linear poly(ethylene oxide) was investigated. Significant ice adhesion reduction, in particular, at temperatures above -15 °C, was observed on silica surfaces coated with the electrostatically anchored diblock copolymer. Differential scanning calorimetry measurements on bulk polymer solutions demonstrate different thermal transitions of water interacting with branched and linear poly(ethylene oxide) (with hydration water melting points of about -18 and -10 °C, respectively). This difference is consistent with the low shear ice adhesion strength measured on surfaces carrying branched bottle-brush structured poly(ethylene oxide) at -10 °C, whereas no significant adhesion reduction was obtained with linear poly(ethylene oxide) at this temperature. We propose a lubrication effect of the hydration water bound to the branched bottle-brush structured poly(ethylene oxide), which, in the bulk, does not freeze until -18 °C.