Emulsions particle size analysis

The most useful parameters commonly measured to assess the effect of stress conditions on emulsions include phase separation, rheological property determination, electrical property measurements, and particle size analysis. 

The self-emulsifying behaviour of a binary nonlonlc surfactant vegetable oil mixture has been shown to be dependant on both temperature and surfactant concentration. The quality of the resulting emulsions as assessed by particle size analysis showed that manipulation of these parameters can result In emulsion formulations of controlled droplet size and hence surface area. Such considerations are Important when the partition of lipophilic drugs Into aqueous phases and drug release rates are considered. 

For the reasons described above, the droplet size distribution of the same emulsion measured on different laser diffraction instruments can be significantly different, depending on the precise design of the optical system and the mathematical theory used to interpret the diffraction pattern. It should be noted, however, that the most common source of error in particle size analysis is incorrect operation of the instrument by the user. Common sources of user error are introduction of air bubbles into the sample, use of the wrong refractive index, insufficient dilution of emulsion to prevent multiple scattering. and use of an unclean optical system. 

Referring to Table 4.8, there are differences between the two homogenizers and types of particle size analysis. However, an independent study (Gooch 2002) showed that emulsification with an APV Homogenizer (3,500 psig) produced an emulsion with a mean particle size of 0.688/1.128 pm (number/volume-weight geometric mean). 

Laser Diffraction Methods Over the past 30 years laser diffraction has developed into a leading principle for particle-size analysis of all kinds of aerosols, suspensions, emulsions, and sprays in laboratory and process environments. 

Particle size analysis in the critical emulsions is a rather complex task, in part due to the high particle concentration. However, such studies were carried out and yielded the size of microdroplets on the order of tens of nm. 

Different properties of the prepared dry adsorbed emulsions were examined (yield value, deteiminadon of dry content, measurement of angle of repose, deter-iiiinatlou of flow rate, density, bulk density, percentage of porosity, particle size analysis. Karl Fisher titrimetry. drug release study, stability study) and the most appropriate selected for in vivo investigation. 

Orlando, FL., Fall 1996, p.34-5. 012 HIGH-RESOLUTION PARTICLE SIZE ANALYSIS OF MOSTLY-SUBMICRON EMULSIONS BY SIMULTANEOUS COMBINATION OF DLS AND SPOS McKenzie C D Wn J S Chang Y J O Hagan P Hasapidis K Particle Sizing Systems... 

The final product was elastic and self-tacking white solid. Upon dissolution in THF and drying, the solid was ttanslucent, indicating a block copolymer structure. Particle size analysis of the latex is shown in Fig. 3.2.4 to have a multimodal distribution, ranging from submicron to 10 p,m or greater, but still a stable enough emulsion. In fact, all of our latex products made from this type of emulsion FRRPP... 

Davis, S. S., Purewal, T. S., and Burbage, A. S., 1976, The particle size analysis of multiple emulsions,/ Pharm. Pharmacal. Suppl. 28 60P. 

Since the initial introduction of laser diffraction instrumentation in the 1970s, many different applications to particle size analysis have been reported. These have included measurements of size distributions of radioactive tracer particles, ink particles used in photocopy machines, ziiconia fibers, alumina particles, droplets from electronic fuel injectors, crystal growth particles, coal powders, cosmetics, soils, resins, pharmaceuticals, metal catalysts, electronic materials, photographic emulsions, organic pigments, and ceramics. About a dozen instrument companies now produce LALLS instruments. Some LALLS instruments have become popular as detectors for size-exclusion chromatography. 

The evaluation of the particle size is often difficult when particles in the submicron range and above 1 xm are simultaneously present. Even in some cases, no usual method is available. Pooley [31] developed an electron microscopic method for particle size analysis of oil-in-water emulsions. It is based on the impression of a water-soluble polymer film by the emulsion particles. 

Davis SS, Biubage AS. 1978. The particle size analysis of multiple emulsions (water-in-oil-in-water). In Particle Size Analysis, Groves MJ, eds. London Heyden, pp 395-410. 

The concepts of average particle size and PSD are discussed in Section 8.2, and the difficulty of obtaining a representative sample for particle size measurements are reviewed in Section 8.3. Approximately, 400 methods for particle size analysis have been reported (Scarlet, 1982). The methods used most frequently for characterizing submicron particles made by emulsion polymerization are reviewed briefly in Section 8.4. Several techniques used for analyzing latexes are compared in Section 8.5. 

Some popular methods of particle size analysis and their ranges of applicability are listed in Table 8.3. The methods used most often to analyze polymer emulsions, described below, are conveniently divided into three categories (a) ensemble techniques (e.g. laser diffraction (LD) and dynamic fight scattering (DLS)) (b) separation techniques (e.g. capillary hydrodynamic fractionation (CHDF) and disk centrifugation) (c) ultrahigh separation techniques (e.g. SPOS and electrozone sensing). 

Analysis of a method of maximizing the usefiilness of smaH pilot units in achieving similitude is described in Reference 67. The pilot unit should be designed to produce fully developed large bubbles or slugs as rapidly as possible above the inlet. UsuaHy, the basic reaction conditions of feed composition, temperature, pressure, and catalyst activity are kept constant. Constant catalyst activity usuaHy requires use of the same particle size distribution and therefore constant minimum fluidization velocity which is usuaHy much less than the superficial gas velocity. Mass transport from the bubble by diffusion may be less than by convective exchange between the bubble and the surrounding emulsion phase. 

Phenomena at Liquid Interfaces. The area of contact between two phases is called the interface three phases can have only aline of contact, and only a point of mutual contact is possible between four or more phases. Combinations of phases encountered in surfactant systems are L—G, L—L—G, L—S—G, L—S—S—G, L—L, L—L—L, L—S—S, L—L—S—S—G, L—S, L—L—S, and L—L—S—G, where G = gas, L = liquid, and S = solid. An example of an L—L—S—G system is an aqueous surfactant solution containing an emulsified oil, suspended soHd, and entrained air (see Emulsions Foams). This embodies several conditions common to practical surfactant systems. First, because the surface area of a phase iacreases as particle size decreases, the emulsion, suspension, and entrained gas each have large areas of contact with the surfactant solution. Next, because iaterfaces can only exist between two phases, analysis of phenomena ia the L—L—S—G system breaks down iato a series of analyses, ie, surfactant solution to the emulsion, soHd, and gas. It is also apparent that the surfactant must be stabilizing the system by preventing contact between the emulsified oil and dispersed soHd. FiaaHy, the dispersed phases are ia equiUbrium with each other through their common equiUbrium with the surfactant solution. 

Particle Size Distribution Determination. To consider the full PSD, a population balance or age distribution analysis on particles must be employed. Table II gives a summary of recent work concerning the determination of PSD s in emulsion systems, using both the "monodispersed" approximation and the population balance approach. More details can be found in the literature sources cited in the Table. 

The characterization of emulsions by particle size distribution analysis has been facilitated in recent years by a range of new instruments. Most of these instruments employ laser light diffraction principles, and have replaced older spectrophotometric methods. 

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