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

Abstract

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.

Breakup of an Elongated Droplet in a Centrifugal Field

“…This breaking thread method was used to measure the interfacial tension by the determination of the breakup growth rate of an elongated liquid drop in the absence of an overall flow field. In our previous experiments, 8 however, the final rotational speed could not be reduced to zero as it was needed to balance the gravitational force on the droplet. It was observed that the breakup velocity depends also on the final rotational speed.…”

“…The interfacial tension in a colloid-polymer suspension, phase separated into a colloidal-gas phase and a colloidal-liquid phase, is very low, on the order of 1-10 µN/m and has recently been studied experimentally [7][8][9] and theoretically. [10][11][12] In the experiments, the interfacial tension was measured with the spinning drop method, which is appropriate to measure such low interfacial tensions.…”

“…8 In these previous experiments it was used to obtain several smaller droplets from a larger one. In 1878, Rayleigh 15 treated the instability of a long, thin, cylindrical liquid thread, and this work was extended by Tomotika 16 in 1935.…”

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

“…In Fig. 2 we compare them for the case Á 2 =Á 1 = 11:6 the value that applies to our experiments [1].…”

“…Recently we studied the interfacial tension between coexisting phases in a phaseseparated colloid-polymer mixture [1,2]. A crude estimate of the interfacial tension is given by the simple scaling relation [3,4].…”