Coalescence, emulsions

67) shows that the larger the difference between ri and T2, the higher the rate of Ostwald ripening. 

Ostwald ripening can be quantitatively assessed from plots of the cube of the radius versus time t [36-38], 

D is the diffusion coefficient of the disperse phase in the continuous phase. Several methods may be applied to reduce Ostwald ripening  

An increase in the surface dilational modulus s (= dy/dln A) and decrease in y would be observed for the shrinking drop and this tends to reduce further growth. 

A-B-A block copolymers such as PHS-PEO-PHS (which is soluble in the oil droplets but insoluble in water) can be used to achieve the above effect. This polymeric emulsifier enhances the Gibbs elasticity and reduces y to very low values. 

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Alkoxylated phenol formaldehyde resins are a well-known class of demulsifier, and the emulsion coalescence data in Table III confirm that Thin Film Spreading Agents, which belong to this class, can also function as chemical demulsifiers. When water in... 

K. Pays Double Emulsions Coalescence and Compositional Ripening. Ph.D thesis, Bordeaux I University (2000). 

S. Magdassi and N. Garti Release of Electrolytes in Multiple Emulsions Coalescence and Breakdown or Diffusion Through Oil Phase Collois Surf. 12, 367 (1984). 

If water is emulsified into fuel as a water-in-oil emulsion, coalescence cannot affect the removal of water from the fuel. The outer oil or surfactant layer surrounding water will not permit water to hydrogen bond to the hydrophilic demulsifier sites. 

It should be noted that the droplet sizes in Hallworth s emulsions are considerably greater than those investigated by Davis and Smith. The importance of the two possible routes of degradation of the emulsions, coalescence or molecular diffusion, may be dependent upon the droplet size and size distribution. Also an interfacial coherent film may reduce the demulsification by either mechanism, i.e. by reducing the rate of coalescence or by presenting an interfacial barrier to... 

Coalescence The merging of two or more droplets into a single droplet. In an emulsion coalescence reduces the total number of droplets and also the total interfacial area. 

For studying emulsion coalescence, it is important to consider the rate constant of flocculation and coalescence. If coalescence is the dominant factor, then the rate K follows a first-order kinetics. 

Emulsion coalescence This can occur if the emulsifier is not strongly adsorbed at the O/W or W/O interface, and results in its partial or complete displacement by the suspension dispersant which is not a good emulsion stabiliser. This in turn... 

Assessment and Prediction of Emulsion Coalescence Using Rheological Techniques I 459... 

From the first glance it is obvious that the same trends syiply to both emulsions, but earlier in the case of emulsion A which may be qualified as h s stable. The way to quantify this concept is to intercept the two curves by a single line. For instance, the (vertical) white-headed arrow locked at a fixed time (here 10 h) intercepts both curves at a point (white dot) whose ordinate indicates the coalesced volume after 10 h. It is larger for emulsion A, which is thus less stable. In the present case there is quite a difference in coalescence fraction VJV between the two emulsions. However, this is not the general case, since the emulsion-coalesced volume fraction does not vary but over a sometimes narrow period of lime. For instance, if the interception is made at 100 h instead of 10 h. then both emulsions are completely coalesced, while after 1 h none of them has started to coalesce. Thus at I h and iOO h the diagnostic is the same for both emulsions, in discrepancy with the actual difference. 

Chem. Descrip. Diethylene glycol butyl ether acetate CAS 124-174 EINECS/ELINCS 204-68 -9 Uses Solvent for high-solids coatings, NC emulsions coalescing aid for wafer-disp. coatings... 

Direct emulsification Emulsion coalescence Emulsion destabilization Microfluidic emulsification Premix emulsification Spontaneous emulsification... 

FIGURE 11.16. Multiple emulsion degradation can take place by several mechanisms. Important pathways include (a) secondary emulsion coalescence with little change in drop size in the PE, (ft) PE drop coalescence with httle change in secondary emulsion characteristics, and (c) loss of PE internal phase to the final external phase due to diffusion or solubilization. 

Figure12.10 Schematic of the system forextraction and emulsion coalescence (a) and photograph of emulsion coalescence device (b). Reproduced by permission of the Royal Society of Chemistry [33].

In general, interfacial energy is a material-specific property influenced by temperature and pressure. Its significance results from the fact that its value rises with any increase in the interfacial area. From an energetic point of view it is, therefore, favourable when, e.g., the droplets of a colloidal emulsion coalesce and, thus, reduce the interfacial area, or when the coarse particles of a colloidal phase grow at the expense of the fine particles (Ostwald ripening). 

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