Droplet drop drainage

As dispersion proceeds drops come into close contact with each other and may coalesce. Coalescence is commonly divided into three sequential steps (Chesters, 1991) collision or close approach of two droplets, drainage of the liquid between the two drops, and rupture of the film (see Fig. 26). 

Dock drainage. Federal regulations require that free oil be removed from deck drainage prior to disposal. It is extremely difficult to predict an oil drop size distribution for rainwater or washdown water collected in an open drain system, and regulations do not define what size droplet is meant by free oil. 

The site of drug deposition in the nasal cavity highly depends on the method of administration. When administering solution formulation, it is important to consider the particle/droplet size. In addition, the limitation is that the entire dose must be given in a volume of 25-200 pL, depending on the formulation. Nasal drops are the simplest and most convenient form. However, the exact volume of dosing is difficult to determine, which may be a device-related matter, and rapid drainage from the nose is another problem with drops. 

Thin liquid films in foam and emulsion systems are usually stabilised by soluble surfactants. During the formation of such films the flow-out process of liquid disturbs the surfactant equilibrium state in the bulk and film surfaces. The situation of drainage of a surfactant containing liquid film between two oil droplets is shown in Fig. 3.15. (after Ivanov Dimitrov 1988). Here j" and are the bulk fluxes in the drops and the film, respectively, j and j are the fluxes due to surface diffusion or spreading caused by the Marangoni effect, respectively. 

Figure 2.7. Illustration of a macroemulsified oil system. The drainage of the film may be reduced due to accumulation of emulsified oil droplets within the plateau borders. The formation of the emulsion film and pseudo-emulsion film are indicated. Factors effecting the foam stability were found to be oil volume fraction, drop size and oil phase density (from ref. (4))...

The temperature can modify the physical properties of oil, water, interfacial fUms and the solubility of surfactants in oily and aqueous phases affecting the stability of an emulsion When increasing the temperature, it is observed a decrease in viscosity of emulsion caused primarily by a decrease in oil viscosity. The temperature increases the thermal energy of drops and, consequently, increases the frequency of drop collisions. This also reduces the interfacial viscosity and results in a rate of faster drainage of the fUtn, thus increasing the coalescence of droplets. The temperature increase leads to a gradual destabilization of interfacial films. 

When the surfactants are soluble in the drop phase, the film drainage is practically the same as in the case of a film between pure solvent phases this has been proven both theoretically and experimentally [484-487]. The flow in the droplet phase is very complicated and the full Navier-Stokes equation have been used by Ivanov and Traykov [486] to obtain the following exact expression for the film drainage velocity ... 

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