Cloud point dispersions

One remaining possibility that is less costly from an energy point of view but needs to be carefully controlled is to incorporate additives called flow improvers. These materials favor the dispersion of the paraffin crystals and in doing so prevent them from forming the large networks which cause the filter plugging. The conventional flow improvers essentially change the CFPP and pour point, but not the cloud point. They are usually copolymers, produced, for example, from ethylene and vinyl acetate monomers ... 

When scouring synthetic fibres that are to be dyed with disperse dyes, nonionic scouring agents are best avoided unless they are formulated to have a high cloud point and are known not to adversely affect the dispersion properties of the dyes. Conversely, when scouring acrylic fibres, anionic surfactants should be avoided [156] because they are liable to interfere with the subsequent application of basic dyes. These fibres are usually scoured with an ethoxylated alcohol, either alone or with a mild alkali such as sodium carbonate or a phosphate. 

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. 

Certain cloud point improvers function by effectively inhibiting the nucleation of wax crystals. This can be accomplished by dispersion of the wax, thus interfering with nucleation. By functioning as an effective dispersant, certain cloud point improvers can help to solubilize water into fuel to give the fuel a cloudy, hazy appearance. As little as 200 ppm of a cloud point improver can create an opaque, relatively stable haze in treated distillate fuel. 

Certain cloud point improvers will disperse water into fuel and create an emulsion or haze. This phenomenon can occur at cloud point improver treat rates as low as 200 ppm. 

Trichlorodifluoroethane (HCFC-122) is a co-spin agent, which lowers the cloud-point pressure. The cloud-point pressure means the pressure at which a single phase liquid solution begins to phase separate. At temperatures above the critical point, there cannot be any liquid phase present and therefore a single phase, supercritical solution phase separates into a polymer-rich/spin fluid-rich, two-phase gaseous dispersion. 

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.

As a result of polydispersity effects, the composition of the incipient 13-phase segregated at the cloud point is located on a shadow curve, outside the cloud-point curve (point (3 in Fig. 8.4). The effects of polydispersity on phase diagrams and phase compositions may be found in specialized reviews (Tompa, 1956 Kamide, 1990 Williams et al., 1997). Because < )Mo < ( M,crit(xcp), the incipient (3-phase, which is richer in the modifier, will be dispersed in the a-phase, which is richer in the growing thermosetting polymer. The opposite occurs when < )M0 > M,crit(xcp)- It has been shown both theoretically (Riccardi et al., 1994 and 1996 Williams et al., 1997), and experimentally (Bonnet et al., 1999) that... 

The effect of cure temperature is more difficult to analyze. An increase of cure temperature produces three different effects an increase of the reaction rate, a decrease of the viscosity, and an increase (UCST) or a decrease (LCST) of the initial miscibility. It has been observed that as the viscosity at the cloud point, r CP, decreases there is an increase in the average size of dispersed phase particles and a corresponding decrease in their concentration. 

CjiEOj is present as a W+L dispersion between 0 and about 30 °C (it does not exhibit a cloud point), and undergoes a transition to a W+L2 system above 30 °C. A comparison of the detergency performance of the lamellar phases of C12E03 and C,2E04 can be made at 30 °C. At 48 °C, the performance of the very hydrophobic phase can be compared with that of the La phase of C12E04 and the Ll phase of C12E03. 

Non-ionic surfactants do not exhibit Krafft points. Rather the solubility of nonionic surfactants decreases with increasing temperature and the surfactants begin to lose their surface active properties above a transition temperature referred to as the cloud point. This occurs because above the cloud point a separate surfactant-rich phase of swollen micelles separates the transition is visible as a marked increase in dispersion turbidity. As a result, the foaming ability of, for example, polyoxyethyle-nated non-ionics, decreases sharply above their cloud points. The addition of electro-... 

From absolute zero (0°K) to 25°C, most hydrophilic solute remains separated in water to an upper critical solution or upper consolute temperature (Tc) (Glasstone and Lewis, 1963) whereupon they merge. In the opposite direction (from high to low temperature), solute and solvent or two solute phases in a common solvent may remain separated to a lower Tc, where they again merge. Many cellulose derivatives have a lower Tc in the vicinity of 45°C. The lower and upper Tc are called cloud points because of the incipient cloudiness observed there. This incipient cloudiness in a formerly translucent dispersion is evidence that the solute has emerged from a secondary minimum on its way to a gel (Walstra et al., 1991). 

After heating at a constant temperature (ca. 35°C), above the cloud point of the mixture, the heterogeneous dispersion was centrifuged at 3400 r.p.m. for 15 min. A deep violet micellar rich upper phase was then obtained. The centrifuge vessels were calibrated in order to allow the measurement of the micellar phase volume aliquots of this layer were taking with a syringe for the analysis. 

It has a medium cloud point, is an excellent emulsifier for oils and waxes, and a good dispersant for particulate matter. 

Figure 2. Cloud point curves of Brij 52/Brij 30 80/20 mixture with a water/surfactant ratio of 5.0, acrylamide/surfactant ratio of 1.0, total dispersed-phase volume fraction of 0.136, and seven continuous- phase ethane concentrations (weight %). ...

Figure 6. Clearing pressure (cloud point) of B52/B30 In 80.4/19.6 w/w ethane/propane with a water/surfactant ratio of 5.0 and an acrylamlde/surfactant ratio of 1.0 versus dispersed-phase volume fraction.

Another property of surfactants is the cloud point of non-ionic surfactants. Below this temperature a single phase of molecular or micellar solution exists above it, the surfactant has reduced water solubility, and a cloudy dispersion results [Biinz, Braun et al., 1998 Katritzky, Maran et al., 2000]. 

My, oo). This new phase boundary for the cloud point of the rubber is shown as the upper curve in Figure 1.34 and will correspond to an extent of conversion pcvphase dispersed in the thermoset (a-)phase and, as shown in Figure 1.34, the theoretical composition of the P-phase will be given by the position on the cloud-point boundary as shown. (It has been noted that this is not strictly correct due to polydispersity effects and the actual composition lies outside this line (Pascault et al, 2002)). 

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