Influence of Colloidal Interactions on Floc Structure

When the attraction between the droplets is relatively strong compared to the thermal energy, the flocs formed have extremely open structures in which each droplet is only linked to two or three of its neighbors (Figure 7.13). This type of open structure is formed because the droplets "stick" firmly together at the point where they first come into contact and are unable to undergo any subsequent structural rearrangements (Bremer 1992). As a consequence, a droplet which encounters a floc cannot move very far into its interior before becoming attached to another droplet. This type of floc is characterized by a tenuous structure which traps large amounts of continuous phase within it. The volume fraction of particles in such a floc may be as low as 0.13 depending on its size and the strength of the interactions (Dickinson 1992). When the attraction between the droplets is relatively weak compared to the thermal energy, the droplets do not always stick together after a collision and they may be able to roll around each other after sticking together. Thus a droplet which encounters a floc is able to penetrate closer to its center and flocs are able to undergo structural rearrangements, which means that the droplets can pack more closely together (Bijsterbosch et al. 1995). This type of floc is characterized by a more compact structure which traps less of the continuous phase. The volume fraction of the particles in this type of floc may be as high as 0.63, which is close to the value for random packing of monodisperse particles (Dickinson 1992).

Floc with Close Floc with Open Packing Packing

FIGURE 7.13 Schematic diagram of some of the different types of structures that flocs may form.

Floc with Close Floc with Open Packing Packing

FIGURE 7.13 Schematic diagram of some of the different types of structures that flocs may form.

FIGURE 7.14 Examples of two-dimensional structures that can be used to model flocs.

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