Adsorption of emulsifier

A stabilising effect in the presence of salt was also noted by Aronson and Petko [90]. Addition of various electrolytes was shown to lower the interfacial tension of the system. Thus, there was increased adsorption of emulsifier at oil/water interface and an increased resistance to coalescence. Salt addition also increased HIPE stability during freeze-thaw cycles. Film rupture, due to expansion of the water droplets on freezing, did not occur when aqueous solutions of various electrolytes were used. The salt reduced the rate of ice formation and caused a small amount of aqueous solution to remain unfrozen. The dispersed phase droplets could therefore deform gradually, allowing expansion of the oil films to avoid rupture [114]. 

Increased fat and increased protein content in the mix delay adsorption of emulsifiers to air. Low temperature also has an inhibiting effect on this phenomenon. Surface tension analysis may be used to measure dosage effect in low-fat ice cream mixes. Such studies show that on a weight basis emulsifier is bound 10 times more strongly to fat than to milk protein in the mix49. 

Type and concentration of emulsifier. The viscosity and yield value of emulsions (chemical nature of the emulsifier. Sherman (1955c) proposed two possible reasons for this, namely interfacial viscosity and interfacial adsorption. Interfacial viscosity affects the resistance of droplets to deformation, which is reflected in the resulting emulsion viscosity. A high level of interfacial adsorption enlarges the size of the interfacial layer significantly and increases emulsion viscosity. Adsorption of emulsifier at the interface should also increase with the concentration of emulsifier. The... 

Qnulsion polymerization of lower alkyl acrylates was studied in terms of Interfacial phenomena. Adsorption of emulsifier depending on its nature reduces during... 

There are two factors that infiuence the particle formation conditions the adsorption of emulsifier on the droplets, which baves less emulsifier in the aqueous phase to facilitate particle formation-there, and the rate of radical absorption in monomer droplets. The former factor may be evaluated by talcing into account the adsorption isotherm of emulsifier on monomer droplets. Using a modified Langmuir adsorption isotherm in combination with a mass balance gives an expression for the aqueous phase concentration of emulsifier C... 

A consideration of the adsorption kinetics is very important m an estimation of the effectiveness of surfactants under the dynamic conditions of emulsion polymerization. In a stalagmometric study of dynamic and static adsorption of emulsifiers of various structure at the air-water interface, it was established that adsorption values of micelle-forming sui c-tants differ significantly in the period of drop formation (Nikitina et ai, 1961). This was explained by the considerable period needed for establishment of adsorption equilibrium connected with the kinetics of adsorption layer formation. The authors concluded tirat for usual concentrations of surfactant solutions the period of estaUishm t of adsorption equilibrium can be taken as equal to 2 min. Figure 2 shows the adsorption isotherms of... 

The adsorption of emulsifiers at fluid-fluid interfaces is considered to play an important role in the formation and stabilization of food dispersions (Dickinson, 1982). During the formation of a dispersed system, the emulsifier must be adsorbed at the interface to prevent the recoalescence of the initially formed dispersed particles (bubbles or droplets). In addition, during... 

The d)mamics of adsorption of emulsifiers at fluid interfaces have been determined by tensiometry and surface rheology (Figure 14.3) that is, from the time dependence of surface pressure and surface dilatational modulus (E). We found that tt and E increase with time (9), which should be associated with emulsifier adsorption (Patino and Nino, 1999 Nino et al., 2003 Carrera et al., 2005). 

Hartland and eoworkers (45-47) have extensively studied the dynamies of emulsifieation and demulsifi-eation of water-in-crude oil emulsion. They found that temperature, the concentration of emulsifier or demul-sifier, and the nature of the medium (erude oil or brine) were very important parameters governing the adsorption of emulsifier at the interface. 

Paxton, T. R., Adsorption of emulsifier on polystyrene and poly(methyl methacrylate) latex particles, J. Colloid Interface ScL, 31, 19-30 (1969). 

Decomposition of peroxodisulfates in the aqueous sodium dodecyl-sulfate solutions (below and above CMC) with and without poly(vinyl chloride) particles and/or vinyl chloride monomer was investigated by Georgescu et al. [94, 95]. They also observed the increase of peroxodisulfate decomposition in the presence of emulsifier (Fig. 4). In contrast, the decomposition rate decreased with increasing particle concentration. The dependence of the initial decomposition rate of potassium peroxodisulfate vs the emulsifier concentration is described by a curve with a maximum at CMC. The catalyzed decomposition of initiator was ascribed to the interaction of initiator with free emulsifier molecules or with emulsifier micelles. The effect of particles was ascribed to the decrease of the water-soluble fraction of emulsifier caused by adsorption of emulsifier on the polymer particle surface. The relationship of the decomposition rate constant vs the emulsifier (sodium dodecyl sulfate) concentration with and without poly(vinyl chloride) particles is described by a curve of the same shape but with different absolute values of k ka is lower in the presence of PVC particles (Fig. 4). The most intensive decomposition of initiator occurs at concentrations close to the CMC. Decomposition of peroxodisulfate recorded with vinyl chloride and poly(vinyl chloride) is faster than in pure water and slower than in emulsifier solutions. Variations in the decomposition rate results from the... 

The dynamic process of adsorption of emulsifiers and the equilibrium state of the interfacial film can be measured by the change in interfacial tension as a function of time. Dynamic interfacial tension techniques exist that measure without disturbing the interface. Various such techniques to measure interfacial tension have been reported in the literature (Addison and Hutchinson, 1949 Padday and Russel, 1960). The Wilhelmy plate technique is preferred over other techniques because the values obtained are more accurate than those obtained using other techniques such as the capillary rise or du Nouy ring methods (Padday and Russel, 1960). In the latter two methods, the long equilibration time (3-60 hours) and difficulties in accurately positioning the... 

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