Fluid-fluid phase separation in colloid-polymer mixtures studied with small angle light scattering and light microscopy

Abstract

Mixtures of colloidal silica spheres and polydimethylsiloxane in cyclohexane with a colloid-polymer size ratio of about one were found to phase separate into two fluid phases, one which is colloid-rich and one which is colloid-poor. In this work the phase separation kinetics of this fluid-fluid phase separation is studied for different compositions of the colloid-polymer mixtures, and at several degrees of supersaturation, with small angle light scattering and with light microscopy. The small angle light scattering curve exhibits a peak that grows in intensity and that shifts to smaller wave vector with time. The characteristic length scale that is obtained from the scattering peak is of the order of a few p.m, in agreement with observations by light microscopy. The domain size increases with time as t 1/3, which might be an indication of coarsening by diffusion and coalescence, like in the case of binary liquid mixtures and polymer blends. For sufficiently low degrees of supersaturation the angular scattering intensity curves satisfy dynamical scaling behavior.

Transient gels in colloid–polymer mixtures studied with fluorescence confocal scanning laser microscopy

“…The scattering proÿles show the Porod decay (I (q) ∼ q −4 ) at high q, thus indicating the presence of sharp interfaces. Both the presence of a ring at non-zero angle and the Porod decay are characteristic for phase separating binary liquid mixtures, and have been observed in colloid-polymer mixtures with a broad attraction range ( p = c = 1) during uid-uid phase separation [8]. This suggests that, for the case of the intermediate range attraction ( p = c = 0:25), the initial phase separation process gets arrested by gelation [13].…”

“…When the colloids are close enough their depletion zones overlap, causing an unbalanced osmotic force. This results in an attractive interaction between the colloidal particles, the range and depth of which can be tuned by the diameter ( p ) and the volume fraction ( p ) of the polymer, giving rise to di erent types of phase diagrams [3][4][5][6][7][8].…”

Measurement of the Interfacial Tension of a Phase-Separated Colloid−Polymer Suspension

“…This system was originally prepared and characterized by Verhaegh in a study of the fluid-fluid transition. 18 The silica colloids are commercially available Ludox spheres (Ludox AS 40%, Dupont) coated with 1-octadecanol (Merck, zur Synthese). The hydrodynamic radius of the particles, obtained by means of dynamic light scattering measurements, is 13 nm with a polydispersity of 19%; the particle density was established at 1.60 g/mL.…”

“…It has become clear that for small polymer to colloid size ratios (<0.3) the transition is of the fluid-solid type, while for large size ratios (>0.3) three different phases can occur: two different fluid phases, i.e., a gaslike and a liquidlike phase, and one solid phase, a colloidal crystal. The mechanism and kinetics of these phase transitions have been studied; not only phenomena such as nucleation and growth and spinodal decomposition have been reported 17,18 but also processes of aggregation and gelation. 17,19 Here, we study the interfacial tension between coexisting phases in a phase-separated colloid-polymer mixture.…”

Wetting in a Colloidal Liquid-Gas System

“…For such a system, the attraction, that causes gas-liquid phase separation, is generated by adding nonadsorbing polymer. This is called depletion interaction and is of entropic nature [9,[11][12][13][14][15][16][17][18]. The interaction free energy of this depletion interaction is given by the product of the overlap volume of two depletion zones and the osmotic pressure due to the polymer.…”