Emulsions life time

The temperature dependence of emulsion stability, evaluated in terms of the emulsion life time , te, was studied simultaneously with the temperature dependence of the surface tension (Fig. VI-4). These studies showed that the stability of emulsions (of noticeable concentrations) in a system with nearly critical composition experienced a sharp increase and... 

Fig. 7.24 depicts the results from the kinetics of destruction of a foamed emulsion produced from 1% NaDoS solution and 0.05% PVA, its drainage and separation of the emulsion from it. The determined period of half-life of the foamed emulsion the time of drainage of one half of the volume of the aqueous solution (tl) and the time for separation of... 

Emnlsion stability may be described by the half-life of the emnlsion following the concept used for foam stability (Sheng et al., 1997). The half-life corresponds to the time at which the emnlsion volume has decayed to half its initial volume. Figure 13.14 shows the half-life times versus droplet volumes for a Daqing-produced fluid. Here, the emulsion was stable for smaller dispersed droplets. The surfactant B-lOO with 0.2% was nsed. 

Figure 13.15 shows the half-life times versus surfactant (B-lOO) concentrations of W/0 and OAV emnlsions withont the presence of alkali (Li, 2007). Here, the W/0 emulsion was more stable than the 0/W emnlsion, and both of the emulsions were more stable at higher surfactant concentrations. There was no alkali in the solution. 

Figure 9 (a) Plot, at 20°C, of the life time z, of internal droplets entrapped in the oil globules as a function of the external phase surfactant concentration Cg. The double emulsions are composed of 90% external phase and 10% double droplets. There is 10% water within the large double globules 2% Span 80 was used within the oil, and SDS in the external water phase, (b) Influence of the internal surfactant concentration Ci on the z =J[Cs) curve, at 20°C. System Span 80/SDS as in Figure 9a. The dashed and solid lines are only guides to the eyes (From Ref. 37.)...

Microemulsion polymerization [114] involves the polymerization of oil-in-water and water-in-oil monomer microemulsions. Microemulsions are thermodynamically stable and isotropic dispersions, whose stability is due to the very low interfacial tension achieved using appropriate emulsifiers. Particle nucleation occurs upon entry of a radical into a microemulsion droplet. Microemulsion polymerization allows the production of particles smaller than those obtained by emulsion polymerization. This leads to a higher number of polymer particles, which results in a more compartmentalized system. Under these conditions, the life-time of the polymer chains increases leading to ultra-high molecular weights. Inverse microemulsion polymerization is used to produce highly efficient flocculants. 

The life time of the transient gel is determined by the strength of the depletion interaction and the colloid concentration and plays a role in many practical systems. For example in salad dressing, which is an oil-in-water emulsion, the depletion flocculation of the oil droplets induced by the addition of a polysaccharide such as xanthan leads to the formation of a particle network [112, 113], The yield stress of this network (in the sense of food science) stabilizes the... 

Many products in the chemical and agrochemical, cosmetic, pharmaceutical, and food industries are emulsion-based. Their internal structure is composed of one or more fluids, with one being flnely dispersed as droplets within the other one. The size distribution of the droplets mainly influences characteristic product properties as color, texture, flow- and spreadability, viscosity, mouth-feel, shelf-life stability, and release of active ingredients. It therefore has to be maintained for the life-time of a product. Due to the extremely high interfacial area in these systems, this microstructure is thermodynamically unstable. By applying emulsiflers and thickeners, emulsions are kinetically stabilized for a certain amount of time. Elowever, shelf-life stability always is a big chal-... 

What type of emulsion do we have What would for this emulsion be the half-life time, if there is no potential barrier ... 

During the Intervals 1 and 11 of a batch emulsion polymerisation, monomers are divided, that is, partitioned, over the monomer droplets, the aqueous phase and the polymer particles. The monomer that is consumed by polymerisation in the polymer particles is replaced by monomer that is transferred from the monomer droplets through the aqueous phase into the particle phase. In Interval 111, there are no droplets and the monomer is mosdy located in the polymer particles. In the semi-batch processes, monomers are continuously fed into the reactor, usually under starved conditions, namely, at high instantaneous conversions, for example, polymer/monomer ratios close to 90/10 on weight bases. Under these circumstances, only the newly fed monomer droplets are present in the reactor and the life-time of these droplets is short because the monomers are transferred through the aqueous phase to the polymer particles where they are consumed by polymerisation. 

Though foam and emulsion films might exist for a long time, on some timescale they will collapse. The rupture of foam and emulsion films has been studied by various methods both experimentally [797] and theoretically [798]. It is obvious that the stability of foam films is influenced by surface forces. For example, in 1924 Bartsch reported that electrolytes decrease the life time of certain foams [799], presumably by decreasing electrostatic stabilization. Surface forces alone, however, do not determine the life time of a soap film. 

Several experiments indicate that the life time of a foam film is correlated with the surface elasticity [738, 786, 800]. One explanation is that high surface elasticities dampen fluctuations in the film [786, 791]. Fluctuations are one possible reason for film rupture. For the same reason, surface viscosity influences the stability of Aims [792, 800]. In particular for large surface-active molecules such as proteins, this has been analyzed for emulsion films due to the importance in food science [721, 793]. The rupture of thin films has been extensively studied for liquid films on solid surfaces. Therefore, we describe it in more detail in Section 7.6.3. 

The residual toxicity of the pure gamma isomer was found to be equivalent to that of ordinary commercial benzene hexachloride. Commercial usage has shown that the residual action is effective for a longer time with dust or wettable powder spray applications than with emulsive solvent-type formulations. The over-all residual life of the chemical is on the order of 4 to 8 days as compared to 14 to 21 days for DDT. This is, of course, adequate residual life for good insect control in most cases and the shorter... 

All samples were evaluated at time zero for total oil, surface oil, moisture, emulsion stability and sensory properties to provide background information for subsequent shelf life testing. Most of the methods were selected based on previous findings (, . 52.) Th results of the total oil, surface oil,... 

The so-called storage stability test is a standard test that is used across many different fields—e.g., the pharmaceutical, cosmetic, and food industries. The test is popular because it yields precise information about the long-term shelf life of emulsions. In this test, emulsions are stored under conditions that are applicable to those encountered in the actual production/consumption situation. It should be noted that the presented test protocol is time consuming and requires sampling over an extended period of time. In the... 

This example demonstrates that storage stability tests are extremely useful as they allow emulsion manufacturers to accurately follow even small changes in emulsion properties. Plots of droplet size distribution and concentration as a function of time can be used to determine the kinetics of the instability process and to determine the shelf life of the product by setting upper and lower limits for both mean droplet size and concentration at each port. 

In an emulsion the dispersed phase is disrupted into droplets. These droplets must be protected from immediate coalescence because emulsions are inherently unstable. Even in a system that appears to be perfectly stable, with a shelf-life of several years, the total number of droplets, their size distribution, and their arrangement in space, are all changing with time. 

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