On the Stability of Emulsions.

An emulsion is a dispersion of one liquid in another and is a thermodynamically unstable system and possesses a natural tendency to break. Stability to flocculation of acoustically formed emulsions and emulsion stability with simultaneous flocculation and creaming has been studied. The stability of acoustically prepared emulsions of C(,36)H(,74) in water was determined by measuring the particle growth rate. The stability was found to decrease with increasing ionic strength, indicating that these emulsions are electrostatically stabilized. Emulsion stability with simultaneous flocculation and creaming was studied by deriving a general dynamic equation (GDE) for emulsion particles. The GDE includes Brownian flocculation, sedimentation-flocculation and creaming. The GDE was solved numerically to predict changes in particle concentration and size distribution as a function of time and position. Cyclic changes in particle size distributions (PSD) are observed when flocculation and creaming occur simultaneously. Initially, the PSD shifts to the right towards larger particle sizes and then reverses and shifts to the left towards smaller particle sizes. An experimental technique has been developed to study the emulsion stability with simultaneous flocculation and creaming. Experiments were carried out by using different ionic strengths, two different dispersants in water (C(,36)H(,74) and C(,28)H(,58)) and different particle size distributions. Experimentally measured changes in particle size distributions are compared with theoretically predicted results. The reverse shift in PSD had been observed both in theory and experiment. There are no adjustable parameters in the theory and the agreement between the theory and experiment is good. A general map presenting regimes of dominant particle loss mechanisms has been developed from which one can determine the dominant particle loss mechanism for a given particle size and density difference between the particles and the continuous medium. The relative importance of flocculation and creaming has been delineated for a monodispersed system. The effect of particle size, surface potential, concentration, density difference, temperature and ionic strength on the relative importance of flocculation and creaming have been delineated.Ph.D.Chemical engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/158720/1/8204743.pd