Emulsions instability

The stability of an emulsion mud is an important factor that has to be closely monitored while drilling. Poor stability results in coalescence of the dispersed phase, and the emulsion will separate into two distinct layers. Presence of oil in the emulsion mud filtrate is an indication of emulsion instability. 

Increasing the temperature can accelerate the development of emulsion instability, thus reducing the required test time however, raising the temperature causes a variety of other... 

Figure D3.4.6 Comprehensive overview of the principal mechanisms that cause emulsion instability.

Thorough investigation of emulsion instability caused by molecular mass transport processes. 

Maleate Surfmers were found to outperform methacrylic and crotonic compounds in the copolymerization of styrene, butyl acrylate and acrylic acid in seeded and nonseeded semicontinuous processes [17]. The maleate Surfmer achieved high conversion without homopolymerization in the aqueous phase which can result in emulsion instability. The methacrylate Surfmer was too reactive as opposed to the crotonate which was not sufficiently reactive. The reported dependence of the maleate Surfmer conversion on the particle diameter is consistent with a reaction at the particle surface. 

Davies and Smith suggest that the effect of addition of small amounts of hexadecane on stability may be due to a prevention of emulsion degradation by molecular diffusion. This approach to emulsion instability was first presented by Higuchi and Misra (12), and was based on the fact that small droplets will demonstrate deviations in physical properties as compared to larger droplets or plane surfaces. 

Emulsion instability and phase separation during viscosity measurements limit the applicability of many of the measurement techniques. This phenomenon is illustrated in Figure 5. The reproducible peak in shear stress with increasing shear rate is related to bitumen separating from this emulsion at the rotor-plate interface of a conventional viscometer. 

Bergenstahl B, Ostberg G. Alkyd emulsion instability and drying properties. In Ref. 1 327-341. 

The neutralized polymer is more hydrophilic than its unneutralized counterpart, and the resulting enhanced compatibility with water would be expected to diminish the driving force for adsorption at the oil-water interface. The emulsion instability at higher pH values for systems containing 0.2% polymer can probably be explained by depletion of hydrophobe at the interface due to the enhanced hydrophilicity of the polymer at these pH values. 

In all these cases the tension temporarily becomes extremely low, in the pN/m range, and very small droplets are formed. Because of the unsteady state, the conditions for emulsion instability are not necessarily met at the same time and the drops might not coalesce at once. As a consequence, a fine emulsion may be produeed, which is not the most stable anyway. In a second step (arrow) the formulation is changed to a more hydrophilic one and some oil is added. Because the efficiency of the stirring decreases in this second step, a bimodal emulsion can be readily made. 

RE Anton, JL Salager. Emulsion instability in the three— phase behavior region of surfactant-alcohol-oil-brine systems. J Colloid Interface Sci 111 54—59, 1986. 

Multisample analytical centrifugation proved to be an efficient tool to predict emulsion instabilities due to floc-... 

Armanet L, Hunkeler D. Manifestation of polyacrylamide inverse-emulsion instabilities through oscillatory shear. Langmuir 2003 19 7164-7172. 

Emulsion instability is manifested in changes in the physical properties of the dispersion such as its droplet size distribution, its rheological properties or other parameters which are a consequence of the coalescence of globules or their flocculation, that is, of the alteration in the real or effective mean globule diameter, respectively. Flocculation, which is often the precursor of coalescence can affect the appearance of both liquid and solid emulsions. It accelerates the rate of creaming or settling which in itself is regarded as a form of instability. 

Thompson et al. [109] studied emulsification and demulsification related to cmde oil production, in particular the role of temperature. The stability of crude oil emulsions was strongly temperature-dependent and in fact demanded the presence of wax crystals. Fat crystals ranged in size from submicrometer to 50 (Am needles. In the temperature range 30-50°C, emulsion instability substan-... 

---