Particle configurations and gelation in capillary suspensions

When a small amount (less than 1%) of a second immiscible liquid is added to the continuous phase of a suspension, the rheological properties of the admixture are dramatically altered and can change from a fluid-like to a gel-like state. These so-called capillary suspensions transition to a gel-like state both if the secondary liquid preferentially wets the particles (pendular state) and even if the secondary liquid wets the particles less well than the primary fluid (capillary state). The mechanism of network formation and the distribution of the secondary liquid in the capillary state has not been investigated so far. Here, we discuss the formation of particle clusters-which are assumed to be the basic building blocks of the observed sample-spanning network-as a function of the contact angle and secondary fluid volume. The presence and strength of these clusters is directly related to the experimentally observed rheological features of capillary state suspensions.