Cloud point stability

In most cases, these active defoaming components are insoluble in the defoamer formulation as weU as in the foaming media, but there are cases which function by the inverted cloud-point mechanism (3). These products are soluble at low temperature and precipitate when the temperature is raised. When precipitated, these defoamer—surfactants function as defoamers when dissolved, they may act as foam stabilizers. Examples of this type are the block polymers of poly(ethylene oxide) and poly(propylene oxide) and other low HLB (hydrophilic—lipophilic balance) nonionic surfactants. 

The adsorption of block and random copolymers of styrene and methyl methacrylate on to silica from their solutions in carbon tetrachloride/n-heptane, and the resulting dispersion stability, has been investigated. Theta-conditions for the homopolymers and analogous critical non-solvent volume fractions for random copolymers were determined by cloud-point titration. The adsorption of block copolymers varied steadily with the non-solvent content, whilst that of the random copolymers became progressively more dependent on solvent quality only as theta-conditions and phase separation were approached. 

Surface-active crown ethers are distinctly differ from usual type of nonionics in salt effect on the aqueous properties, due to the selective complexing ability with cations depending on the ring size of the crown. As shown in Figure 3 (22), the cloud point of the crowns is selectively raised by the added salts. This indicates that the degree of cloud point increase is a measure of the crown-complex stability in water (23). 

Many different types of interaction can induce reversible phase transitions. For instance, weak flocculation has been observed in emulsions stabilized by nonionic surfactants by increasing the temperature. It is well known that many nonionic surfactants dissolved in water undergo aphase separation above a critical temperature, an initially homogeneous surfactant solution separates into two micellar phases of different composition. This demixtion is generally termed as cloud point transition. Identically, oil droplets covered by the same surfactants molecules become attractive within the same temperature range and undergo a reversible fluid-solid phase separation [9]. 

Yon should prove to yourself that it makes no difference if we differentiate with respect to component A or B, nor whether we differentiate with respect to mole or volnme fraction, since the derivatives are set eqnal to zero.) The locns of points swept out by the stability condition shown in Eq. (2.36) at various temperatures is called the binodal, or cloud point curve. For example, just as we drew tangents to the... 

The addition of salts to the aqueous phase of concentrated emulsions can have profound effects on their stabilities. Water-in-oil HIPEs are generally stabilised by salt addition [10,12,13,21,80,90,112] however, the nature of the salt used was found to be important [13]. Salts which decrease the cloud point of the corresponding nonionic surfactant aqueous solutions, i.e. which have a salting-out effect, were more active. The interactions of the surfactant molecules at the oil/water interface were increased due to dehydration of the hydrophilic ethylene oxide groups on addition of salt. This was verified experimentally [113] by an ESR method, which demonstrated that the surfactant molecules at the oil/water interface become more ordered if the salt concentration is increased. 

An additional problem may arise in the lacking cold temperature change stability of the formulated oils, i.e., the cold filter plugging point value of the oils attained rises gradually when the oil is stored for a prolonged period at changing temperatures in the region of the cloud-point or below. 

Downhole wax inhibitor injection will not he required since the stabilized flowing temperature within the well tubing and at the wellhead will be some 55°C which is wpll above the cloud point and wax dissolution... 

In recent years, the middle distillates have been in growing demand as fuel oils and Diesel fuel. As mentioned under the discussion on Diesel-fuel additives, it has been possible to meet this demand only by the inclusion of distillates from catalytic cracking operations. These have higher volumetric heat contents and lower pour and cloud points, but their use has caused problems of stability and compatibility in storage, necessitating use of anti-screen-clogging agents (14, 41, 4 )-... 

Figure 6. Conventional two-component phase behavior in poly disperse Flory-Huggins theory, shown in the (p, p0) plane for three values of % As in Fig. 5, the parent has Ln = 100 and Ly/ = 150 (hence a = 2). Along the y-axis, we plot L//p0 rather than p0 so that the dilution line p = LNp0, shown as the thick solid line in (a-c), is simply along the diagonal. With x considered as an additional variable, the dilution line constraint defines a plane (p, = L/vPq, x)- The last plot, (d), shows the cut by this plane through the phase behavior in (a-c) the solid line is the cloud point curve, and the dashed line is the spinodal stability condition.

A.T. Florence, F. Madsen and F. Puisieux, Emulsion stabilization by nonionic surfactants the relevance of surfactant cloud point, J. Pharm. Pharmacol. 27 (1975) 385-394. 

When a lyophilic colloid loses stability, a separation into two liquid phases may occur. This process is termed coacervation . The phase that is more concentrated in the colloid is the coacervate, and the other phase is the equilibrium solution. See also Cloud Point. 

Also reported for comparison are the curves relative to two non polymerizable salts, sodium acetate and sodium chloride which cause a salting out of the surfactant. The role of electrolytes in the stabilization of the polymerized systems will be discussed below. The cloud point shift values, for the surfactant blend, measured after addition of a unimolal electrolyte solution are listed in Table II. 

Emulsions stabilized by paraffin are usually restricted to light crude oils in oil-field production. If paraffin deposition that restricts production is occurring upstream of an oil-treating facility, it may be feasible to apply a paraffin crystal modifier to the crude oil to prevent paraffin deposition and to eliminate paraffin as an emulsifying agent. A paraffin crystal modifier must enter an oil system at a temperature greater than the cloud point of the crude oil and upstream of the problem area. 

Poloxamers are neutral block copolymers such as 12, consisting of two terminal hydrophilic polyoxyethylene blocks flanking a central hydrophobic polyoxypropylene block. Poloxamer 188 (e.g., Pluronic F-68) was used in the first generation PFC emulsions, but was far from adequate Its surface activity is relatively poor, translating into low emulsions stability the purity of the commercial products is usually rather low its cloud point ( 110-115°C) prevents sterilization at the standard temperature of 121°C its tendency to form gels limits the PFC concentration in the emulsions and, finally, Pluronic F-68 has been found to be responsible for the unpredictable transientcomplement activation-mediated anaphylactic reaction observed in some patients in response to the injection of Fluosol. ... 

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