Capillary Condensation and Interface Structure of a Model Colloid-Polymer Mixture in a Porous Medium

We consider the Asakura-Oosawa model of hard sphere colloids and ideal polymers in contact with a porous matrix modeled by immobilized configurations of hard spheres. For this ternary mixture a fundamental measure density functional theory is employed, where the matrix particles are quenched and the colloids and polymers are annealed, i.e. allowed to equilibrate. We study capillary condensation of the mixture in a tiny sample of matrix as well as demixing and the fluid-fluid interface inside a bulk matrix. Density profiles normal to the interface and surface tensions are calculated and compared to the case without matrix. Two kinds of matrices are considered: (i) colloid-sized matrix particles at low packing fractions and (ii) large matrix particles at high packing fractions. These two cases show fundamentally different behavior and should both be experimentally realizable. Furthermore, we argue that capillary condensation of a colloidal suspension could be experimentally accessible. We find that in case (ii), even at high packing fractions, the main effect of the matrix is to exclude volume and, to high accuracy, the results can be mapped onto those of the same system without matrix via a simple rescaling.Comment: 12 pages, 9 figures, submitted to PR

Breakup of an elongated droplet in a centrifugal field

The breakup of an elongated drop in the presence of a centrifugal field was studied. The system used was a phase-separated colloid-polymer suspension; the elongated drop consisted of the lighter polymer-rich fluid phase and the surrounding fluid was its coexisting colloid-rich fluid phase. We found that the growth rate of the fastest growing disturbance of the drop, which eventually leads to its breakup, is decreasing upon an increase of the rotational speed, whereas the wavelength of the disturbance is increasing upon an increase of the rotational speed. We present a simple analysis of the effect of the centrifugal field which accounts quantitatively for these features. Furthermore, this analysis allows for the determination of the interfacial tension from the measured growth rates

Measurement of the interfacial tension of a phase-separated colloid-polymer suspension

We studied the interfacial tension between coexisting colloid-rich and polymer-rich fluid phases in a phaseseparated colloid-polymer mixture. First, the location of the fluid-fluid binodal and the tie lines between the coexisting phases were determined using a recently proposed method that only requires the volumes of the coexisting phases as input. The spinning drop method was used to determine the very low interfacial tension between the coexisting phases. We also used the dynamics of the breakup process of the droplet of one phase suspended in the other to determine the interfacial tension

The break-up of a liquid cylinder in a centrifugal field

A simple model for the effect of a centrifugal field on the break-up of a long liquid cylinder is developed. The results are in qualitative agreement with recent observations

Food colloids under oral conditions

Recent studies have made clear that structural and rheological changes of soft foods when they are processed in the mouth play a crucial role in sensory perception. This applies to soft solid products (fracturing behaviour and exudation of fluid) as well as more liquid food systems (breakdown of starch by salivary amylase, saliva-induced droplet aggregation, deposition and retention of food material on the tongue surface)

Food colloids under oral conditions

Recent studies have made clear that structural and rheological changes of soft foods when they are processed in the mouth play a crucial role in sensory perception. This applies to soft solid products (fracturing behaviour and exudation of fluid) as well as more liquid food systems (breakdown of starch by salivary amylase, saliva-induced droplet aggregation, deposition and retention of food material on the tongue surface)