DLVO theory between droplets

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 ... 

Two approaching emulsion droplets may be resisted by electrostatic forces. Electrostatic forces consist of Coulombic repulsion between two like charged objects and attractive van der Waals forces. These two forces are accounted for by the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory. A third force. Born repulsion, occurs at very small separation distances when electron clouds overlap [1,6,20,21], In emulsion systems an electrical double-layer may form around the disperse phase droplets. While electrical double-layer repulsion is certainly important in o/w emulsions, it does not play a large role in the stabilization of w/o emulsions due to the low dielectric constant of oil [55,56],... 

DLVO theory was applied (63,64) for the description of spontaneous and forced thinning of the liquid film separating the droplets. These experimental results and DLVO theory were used (63) for the interpretation of the reported visual study of coalescence of oil droplets 70—140 pm in diameter in water over a wide pH interval. A comparison based on DLVO theory and these expermental data led the authors to condlue (63) that if the total interaction energy is close to zero or has a positive slope in the critical thickness range, i.e., between 30 and 50 nm, flie oil drops should be expected to coalesce. In the second paper (64), where both ionic strength and pH effects were studied, coalescence was observed at constant pH values of 5.7 and 10.9, when the Debye thickness was less than 5 nm. The main trend in our experiments and in Refs 63 and 64 were in accordance, because it was difficult to establish the decrease in t.d.c at NaCl concentrations lower than 5 x 10 M, i.e., double-layer (DL) thicknesses larger than 5 nm. An almost quantitative coincidence in the double-layer influence on... 

To estimate colloidal forces acting between the droplets during the collision, x, z coordinates of the initial (x, Zj) and final (xf, Zf) positions of the mobile droplet before and after the collision are needed. When several pairs of x, z coordinates are plotted on a graph a speeifie seattering pattern will appear. This pattern can be analyzed by eompar-ing the experimental final positions with the ones ealeulated from a theory (2,3), which covers hydrodynamic interactions between the droplets and between the mobile droplet and the wall as well as all external forees aeting on the mobile drop, e.g., those described by DLVO theory. Thus, in the calculations, we assume the existenee of a certain force described by a certain function of the droplet-droplet separation. The final position of the droplet is then calculated and compared with the experimental results. The best match between experimental and theoretical final droplet positions yields the optimum set of parameters or the optimum force-distance profile. 

In order to get an idea as to how the interaction energy (Fint( pp)) between two approaching droplets changes as a function of the distance (dpp) of their surfaces, equations (8.20a)-(8.20c) from ref. (51) are quite useful. These equations describe, according to the DLVO theory, the interaction of electrostatically... 

Surface forces are well known and are important in colloid science. They determine the stability and behavior of colloidal suspensions and emulsions [2]. In the case of emulsions/suspen-sions, their properties and behavior (stability, instability, rheology, interactions, and so oti) are governed by surface forces acting between colloidal particles or droplets [2]. The corresponding theory is widely referred to as DLVO flieory [1] according to the names of four scientists who substantially contributed to the area Deijaguin, Landau, Vervey, and Overbeek. 

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