Repulsive interactions between droplets

Addition of Kryptofix 222 and Kronenether to reverse micellar system induces no changes in the droplet size and an increase in the droplet-droplet interactions. The complexation of cations Na of AOT led to a decrease in counterion binding, and consequently repulsive interactions between polar head groups of AOT surfactant are increasing. This could induce a more flexible interface of reverse micelles. 

The structure of the microemulsion depends on the interaction between droplets. In the case of repulsive interaction, the collisions of the droplets are short and no overlapping occurs between their interfaces. However, if the... 

Reduced electrostatic repulsion. Electrostatically stabilized emulsions may flocculate when the electrostatic repulsive interactions between the droplets are reduced. This can be achieved by altering the pH so that the electrical charge on the droplets is reduced, adding multivalent counter ions that bind to the surface... 

Increased depletion attraction. The presence of nonadsorbing colloidal particles, such as biopolymers or surfactant micelles, in the continuous phase of an emulsion causes an increase in the attractive force between the droplets due to an osmotic effect associated with the exclusion of colloidal particles from a narrow region surrounding each droplet. This attractive force increases as the concentration of colloidal particles increases, until eventually, it may become large enough to overcome the repulsive interactions between the droplets and cause them to flocculate (68-72). This type of droplet aggregation is usually referred to as depletion flocculation (17, 18). 

Theoretical Aspects, The basic concept of DLVO theory is that the stability of a colloid can be described in terms of the repulsive and attractive interactions between droplets ... 

The structure of the microemulsion depends on the interaction between droplets. In the case of repulsive interaction, the collisions of the droplets are short and no overlapping occurs between their interfaces. However, if the interactions are attractive, transient droplet elusters are formed. The number of such clusters increases, when the water fraction, the temperature, the pressure, or die ratio of water to surfactant is increased, leading to a percolation in the system (95-101). 

Figure 5 Principle of the colloidal collider method. The shear flow is created between upper fixed plate and the mobile bottom of the cell. The insert shows several consecutive positions of the mobile droplet as it passes around the stationary one. The dotted line depicts a symmetrical trajectory expected when no surface forces exist. The dashed line shows the experimental trajectory indicating a repulsive interaction between the two droplets.

The above trend is also observed if G, G, and G" are plotted versus This is illustrated in Figure 16 for the above emulsions at a frequency of 2 Hz. At ( ) < 0.56, G" > G, whereas at c ) > 0.56, G > G". This reflects the increase in steric interaction with increase in ( ). At c ) < 0.56, the droplet-droplet separation is probably larger than twice the adsorbed layer thickness and hence the adsorbed layer are not forced to overlap or compress. In this case, the repulsive interaction between the adsorbed layers is relatively weak and the emulsion shows a predominantly viscous response. However, when > 0.56, the droplet-droplet separation may become smaller than twice the adsorbed layer thickness and the chains are forced to interpenetrate and/or compress. This leads to strong steric repulsion and the emulsion shows predominantly elastic response. The higher the ( ) value, the smaller the distance between the droplets and the stronger the steric interaction. This explains the rapid increase in G as ( ) increases above 0.56 and the progressively larger value of G relative to G". 

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