Droplet size analysis

Emulsions are prepared using various ratios of the two surfactants. The total surfactant concentration is kept constant (e.g., 10%) based on the oil phase typically, for a 50 50 emulsion, 5% surfactant is used. The emulsions are placed in cylinders and their stability is assessed by visual inspection (looking for any oil separation), by droplet size analysis (e.g., using a Malvern Master Sizer), and by measuring the interfacial tension. For an 0/W emulsion the stability, droplet size and interfacial tension are plotted as a function of the % surfactant with a high HLB number. The stability reaches a maximum at an optimum % of the surfactant with the high H LB number, and at this optimum ratio the droplet size and interfacial tension reach a minimum. For W/O emulsions, the stability droplet size and interfacial tension are plotted versus % surfactant with a low FI LB number. The stability reaches a maximum at an optimum % of the surfactant with the low H LB number, and at this optimum ratio the droplet size and interfacial tension reach a minimum. 

In the absence of any flocculation, the coalescence of an emulsion results in a reduction of its viscosity. At any given volume fraction of oil, an increase in droplet size will result in a reduction of viscosity, and this is particularly the case for concentrated emulsions. Thus, by following the decrease in emulsion viscosity with time, information may be obtained on its coalescence. However, care should be exercised when applying simple viscosity measurements, particularly if flocculation occurs simultaneously (as this results in an increased viscosity). It is possible - at least in principle - to predict the extent of viscosity reduction on storage by combining the results of droplet size analysis (or droplet number) as a function of time with the reduction in viscosity during the first few weeks. 

A very careful study of the kinetics of coalescence of an oil/water emulsion using photomicrographic droplet size analysis was done by Lawrence and Mills (17). They prepared their emulsions by homogenization. Their technique was recently modified by us to determine emulsion stability in petroleum sulfonate systems of interest in chemically enhanced oil recovery processes. These observations are given elsewhere ( , 7). ... 

C. Washington and T. Sizer, Stability of TPN mixtures compounded from Lipofundin S and Aminoplex amino-acid solutions Comparison of laser diffraction and Coulter counter droplet size analysis, Int. J. Pharm. 83, 227-231 (1992). 

Droplet size analysis is of particular interest to both the food industry, for margarine, and to the cosmetic industry, for various make-up emulsions. Droplet size is also a good example of the use of magnetic field gradients to encode spatial in-... 

Visualization Tests, Droplet Size Analysis and Viscosity Measurements... 

Droplet size analysis was used for characterization of the emulsions just prepared and to detect alterations of emulsions during storage. The analysis was conducted using laser diffraction with polarization intensity differential scattering (PIDS) technology (Coulter LS 230, Beckman-Coulter, Krefeld, Germany). 

The above investigations, using droplet size analysis and microscopy investigations can be used to study the effect of rheology on the break-up of non-Newtonian food products. It also allows one to study the mouthfeel, using panels, and some correlations between rheology and mouth feel may be obtained. 

Several methods can be applied for characterization of multiple emulsions (i) Droplet size analysis The droplet size of the primary emulsion (internal droplets of the multiple emulsion, are usually in the region 0.5-2 pm, with an average of 0.5-1.0pm. The multiple emulsion droplets cover a wide range of sizes, usually... 

Emulsions are then prepared using the various surfactant mixtures and their stability determined using droplet size analysis versus time measurements or simply by observing emulsion separation. With O/W emulsions, the stability of the emulsion increases as the proportion of the surfactant with the high HLB number increases and it reaches a maximum at an optimum ratio of the two surfactants (optimum HLB number) after which the stability decreases with further increase of the smfactant with the high HLB number. 

Ultrasonically assisted extraction is also widely used for the isolation of effective medical components and bioactive principles from plant material [195]. The most common application of low-intensity ultrasound is as an analytical technique for providing information about the physico-chemical properties of foods, such as in the analysis of edible fats and oils (oil composition, oil content, droplet size of emulsions, and solid fat content) [171,218]. Ultrasonic techniques are also used for fluids characterisation [219]. 

Inertial impaction is the method of choice for evaluating particle or droplet size delivery from pharmaceutical aerosol systems. This method lends itself readily to theoretical analysis, ft has been evaluated in general terms [39] and for specific impactors [40]. Inertial impaction employs Stokes law to determine aerodynamic diameter of particles being evaluated. This has the advantage of incorporating shape and density effects into a single term. 

In practical fan sheet breakup processes, sheet thickness diminishes as the sheet expands away from the atomizer orifice, and liquid viscosity affects the breakup and the resultant droplet size. Dombrowski and Johns[238] considered these realistic factors and derived an analytical correlation for the mean droplet diameter on the basis of an analysis of the aerodynamic instability and disintegration of viscous sheets with particular reference to those generated by fan spray atomizers ... 

Recently, Razumovskid441 studied the shape of drops, and satellite droplets formed by forced capillary breakup of a liquid jet. On the basis of an instability analysis, Teng et al.[442] derived a simple equation for the prediction of droplet size from the breakup of cylindrical liquid jets at low-velocities. The equation correlates droplet size to a modified Ohnesorge number, and is applicable to both liquid-in-liquid, and liquid-in-gas jets of Newtonian or non-Newtonian fluids. Yamane et al.[439] measured Sauter mean diameter, and air-entrainment characteristics of non-evaporating unsteady dense sprays by means of an image analysis technique which uses an instantaneous shadow picture of the spray and amount of injected fuel. Influences of injection pressure and ambient gas density on the Sauter mean diameter and air entrainment were investigated parametrically. An empirical equation for the Sauter mean diameter was proposed based on a dimensionless analysis of the experimental results. It was indicated that the Sauter mean diameter decreases with an increase in injection pressure and a decrease in ambient gas density. It was also shown that the air-entrainment characteristics can be predicted from the quasi-steady jet theory. 

The studies on the performance of effervescent atomizer have been very limited as compared to those described above. However, the results of droplet size measurements made by Lefebvre et al.t87] for the effervescent atomizer provided insightful information about the effects of process parameters on droplet size. Their analysis of the experimental data suggested that the atomization quality by the effervescent atomizer is generally quite high. Better atomization may be achieved by generating small bubbles. Droplet size distribution may follow the Rosin-Rammler distribution pattern with the parameter q ranging from 1 to 2 for a gas to liquid ratio up to 0.2, and a liquid injection pressure from 34.5 to 345 kPa. The mean droplet size decreases with an increase in the gas to liquid ratio and/or liquid injection pressure. Any factor that tends to impair atomization quality, and increase the mean droplet size (for example, decreasing gas to liquid ratio and/or injection pressure) also leads to a more mono-disperse spray. 

As described above, a number of empirical and analytical correlations for droplet sizes have been established for normal liquids. These correlations are applicable mainly to atomizer designs, and operation conditions under which they were derived, and hold for fairly narrow variations of geometry and process parameters. In contrast, correlations for droplet sizes of liquid metals/alloys available in published literature 318]f323ff328]- 3311 [485]-[487] are relatively limited, and most of these correlations fail to provide quantitative information on mechanisms of droplet formation. Many of the empirical correlations for metal droplet sizes have been derived from off-line measurements of solidified particles (powders), mainly sieve analysis. In addition, the validity of the published correlations needs to be examined for a wide range of process conditions in different applications. Reviews of mathematical models and correlations for... 

The substantial effect of secondary breakup of droplets on the final droplet size distributions in sprays has been reported by many researchers, particularly for overheated hydrocarbon fuel sprays. 557 A quantitative analysis of the secondary breakup process must deal with the aerodynamic effects caused by the flow around each individual, moving droplet, introducing additional difficulty in theoretical treatment. Aslanov and Shamshev 557 presented an elementary mathematical model of this highly transient phenomenon, formulated on the basis of the theory of hydrodynamic instability on the droplet-gas interface. The model and approach may be used to make estimations of the range of droplet sizes and to calculate droplet breakup in high-speed flows behind shock waves, characteristic of detonation spray processes. 

Electrical methods involve the detection and analysis of electronic pulses generated by droplets in a measurement volume or on a wire. The electronic signals are then converted into digital data and calibrated to produce information on droplet size distribution. A detailed review of electrical methods for droplet size measurements has been made by Jones.[657]... 

The Malvern particle sizer is one of the most widely used, most effective, simple, and reliable methods commercially available for rapid measurements of ensemble characteristics of a spray. It is able to handle high droplet concentrations. It is easy to use and does not require comprehensive knowledge of its basic principles for operation. The primary advantage of the system is the speed of data acquisition and analysis. In addition, measurements of droplet size distributions can be made at any droplet velocities due to the fact that the diffraction patterns generated by droplets are independent of the... 

Benkestock, K., Sundqvist, G., Edlund, P. O., Roeraade, J. Influence of droplet size, capillary-cone distance and selected instrumental parameters for the analysis of... 

R. Although expressions for this parameter exist, they are derived by a hybrid of molecular mechanical and thermodynamic arguments which are not at present known to be consistent as droplet size decreases (8). An analysis of the size limitation of the validity of these arguments has, to our knowledge, never been attempted. Here we evaluate these expressions and others which are thought to be only asymptotically correct. Ve conclude, from the consistency of these apparently independent approaches, that the surface of tension, and, therefore, the surface tension, can be defined with sufficient certainty in the size regime of the critical embryo of classical nucleation theory. 

Adapting the evaporative light scattering device (ELSD) to pHPLC was investigated by Gaudin et al. Quantitative analysis by ELSD is often hindered by nonlinearity however, reduction of the flow rate, resulting in better homogeneity of droplet size distribution, has increased the linearity of the response with ELSD. Despite the predictable effect on droplet size in relation to the reduction of the inner diameter of the capillary inside the nebulizer, ELSD is relatively simple to adapt to micro/ capillary EC. ... 

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