INFLUENCE OF THE DISPERSED PHASE DISTRIBUTION ON THE ELECTRICAL-CONDUCTIVITY OF LIQUID O W MODEL AND DAIRY EMULSIONS/

The influence of the dispersed phase volume fraction (0.01 less than o r equal to phi less than or equal to 0.4) and emulsification parameter s (8 less than or equal to P less than or equal to 76 MPa and 35 less than or equal to T less than or equal to 100 degrees C) on the relativ e electrical conductivity(sigma(s)/sigma(2s)) of dairy model emulsions , reconstituted milk and creams, and commercial chocolate milks was st udied. This study was based both on the use of statistically analyzed experimental designs and classical conductivity models of dispersed sy stems (Rayleigh-Wiener, Bruggeman, and Bottcher-Landauer). Furthermore , a simple approximation, based on Eveson's work on the relative visco sity of dispersed systems and derived from the Rayleigh-Wiener equatio n, was also proposed. This equation describes the electrical conductiv ity of dispersed systems composed of n classes of dispersed droplets, [GRAPHICS] with sigma(1s)(r) = sigma(1s)/sigma(2s), and where sigma(s) , sigma(1s), and sigma(2s) are, respectively, the conductivities of th e whole dispersion, the dispersed phase, and the continuous medium. Th is equation, which is applicable to all systems composed of n differen t size classes of dispersed particles, represents the link between the Rayleigh-Wiener equation, only valid for monodispersed systems, and t hat of Bruggeman, valid for infinitely polydispersed systems. The use of the experimental design indicated that only the dispersed phase vol ume fraction, which explained 94% of the total variance, had a statist ically significant effect on the model emulsion sigma(s)/ sigma(2s) ra tio. Emulsification factors were found to have no measurable effect on the conductivity. A comparison with theoretical equations revealed th at if all experimental data (with the exception of chocolate milks) fe ll on lines corresponding to the above four models, for phi less than or equal to 0.15, only the model of Bruggeman and the above equation f or n = 3 or 4 allowed a satisfactory description of the conductive beh avior of this type of emulsion for the whole domain of phi studied. Mo reover, the number n = 3 or 4 of different fraction sizes is a theoret ical number as it is clear that the fat globule size distribution of a dairy emulsion is both continuous and polydispersed. (C) 1994 Academi c Press, Inc.