Emulsions temperature effects

Table 5 illustrates the effects of emulsion thickness on resolution as indicated by HD (distance from the line within which 50% of all the silver grains from it lie). The data indicate that resolution is improved as emulsion thickness is decreased. If the emulsion thickness exceeds 2 pm, an insignificant quantity of (3-particles (see radioisotopes) will reach the emulsion from most biological specimens. Some factors which influence emulsion thickness include dilution of the emulsion, temperature of the emulsion, temperature and wetness of the slide as well as the temperature and humidity during drying. The reader is referred to Rogers (7) for thorough discussions of each. 

The process involves removal of materials less dense than water (such as oil) and suspended materials that are more dense than water by settling. The API separator does not separate substances in solution, nor does it break emulsions. The effectiveness of a separator depends on the temperature of the water, the density and size of the oil globules, and the amounts and characteristics of the suspended materials. The susceptibility to separation (STS) test is normally used as a guide to determine what portion of the influent to a separator is amenable to gravity separation [38]. In terms of globule size, an API separator is effective down to globule diameters of 0.015 cm (15 microns). 

Nonionic surfactants tend to show the opposite temperature effect As the temperature is raised, a point may be reached at which large aggregates precipitate out into a distinct phase. The temperature at which this happens is referred to as the cloud point. It is usually less sharp than the Krafft temperature.2 The phenomenon that nonionic surfactants become less soluble at elevated temperature will be important when we discuss the phase behavior of emulsions. 

Finally, although temperature had a large effect on both the position (wavelength) and the intensity of the water absorption bands in the emulsion NIR spectra, careful experimentation demonstrated that the 1618 nm vinyl C—H band used in the calibration model did not shift in either position or intensity with temperature, in the temperature range used in these studies (25-75° C). Therefore, it was not necessary to correct the calibration model for temperature effects, either by the use of internal or external standards, or by including temperature variations in the calibration set. 

The HLB system used above does not take into consideration the temperature effects. Upon heating, an O/W emulsion prepared with nonionic surfactants inverts to a W/O emulsion because the hydrogen bondings in the polyoxyethylene groups are broken, and the HLB value of the surfactant becomes smaller. The higher the... 

Benzoic Add, USP. Benzoic acid and its esters occur naturally in gum benzoin and in Peru and tolu balsam.s. It is found as a white crystalline solid that slowly sublimes at room temperature and is steam distillable. It is slightly soluble in water (0.3%) but more. soluble in alcohol and in other polar organic. solvents. It has a pK of 4.2. Benzoic acid is used externally as an antiseptic in lotions, ointment.s. and mouthwashes. It is mure effective as a preservative in foods and pharmaceutical products at low pH (Ic.ss than the pK ). When used as a preservative in emulsions, its effectiveness depends on both pH and distribution into the two pha.scs. ... 

The present paper deals with kinetics of coagulation of Phthallylsulfathiazole stabilized xylene in water emulsion in the presence of some cationic detergents. Rate of flocculation, rate of coalescence and rate of creaming have been determined. To estimate the stability of the present systems their zeta potentials have been measured and stability factors calculated. Temperature effect on the system was also studied. 

It is evident from the date recorded in Table I that at higher temperature coalescence rate constant is higher, that is in order of kc30° < kc40° < c50° The temperature effect for all detergents was found to be in the order LPC < CTAB < CPC < CPB. This implies that in the presence of CPB the coalescence rate constant of the emulsions increases enormously (e.g. four to six times for every 10°C rise of temperature) with the rise of temperature whereas in the presence of LPC the increase in the rate is not that pronounced. 

The temperature affects strongly both the solubihty and the surface activity of nonionic surfactants (165). It is well known that at higher temperatures nonionic surfactants become more oil soluble, which favors the W/0 emulsion. These effects may change the type of emulsion formed at the phase-inversion temperature (166). The temperature effect has numerous implications, two of them being the change in the Gibbs elasticity, Eq, and the interfacial tension, o. 

The potential importance of the temperature effect on surfactant properties has been recognized for some time and led to the concept of using the PIT as a quantitative tool for the evaluation of surfactants in emulsion systems. As a general procedure, emulsions of oil, aqueous phase, and approximately 5% surfactant were prepared by shaking at various temperatures. The temperature at which the emulsion was found to be inverted from o/w to w/o (or vice versa) was then defined as the PIT of the system. Since the effect of temperature on the solubility of nonionic surfactants is reasonably well understood, the physical principles underlying the PIT phenomenon follow directly. 

Rate and Temperature Effects. Like adhesive tack, autohesion of elastomers is strongly dependent on test rate and temperature. Furthermore, as shown in Figure 13 for the T-peel autohesion of a cold emulsion SBR, relative autohesion Pr (for a given time and pressure of contact) is not unique, but it too depends markedly on test conditions (104). 

Reducing agents are employed to return the Fe + to Fe +. By starting at a lower temperature, the heat of reaction can be balanced by the sensible heat of the water in the emulsion. Temperature profiles from 20 to 70°C are typical for such systems. Care must be taken when working with redox systems to eliminate oxygen from the reactor before beginning the polymerization. The effectiveness of... 

Several references were made above to the term phase inversion temperature. With the exceptions of Eqs. (9.17) and (9.18), however, no specific reference was made to the effect of temperature on the HLB of a surfactant. From the discussions in Chapter 4, it is clear that temperature can play a role in determining the surface activity of a surfactant, especially nonionic amphiphiles in which hydration is the principal mechanism of solubilization. The importance of temperature effects on surfactant solution properties, especially the solubility or cloud point of nonionic surfactants, led to the evolution of the concept of using that property as a tool for predicting the activity of such materials in emulsions. Since the cloud point is defined as the temperature, or temperature range, at which a given amphiphile loses sufficient solubility in water to produce a normal surfactant solution, it was assumed that such a temperature-driven transition would also be reflected in the role of the surfactant in emulsion formation and stabilization. 

Nitrile Rubber. Nitrile mbbers are made by the emulsion copolymerization of acrylonitrile (9—50%) and butadiene (6) and designated NBR. The ratio of acrylonitrile (ACN) to butadiene has a direct effect on the properties on the nature of the polymers. As the ACN content increases, the oil resistance of the polymer increases (7). As the butadiene content increases, the low temperature properties of the polymer are improved (see Elastomers, SYNTHETIC-NITRILE RUBBER). 

---