| dc.description.abstract |
<p>This thesis addresses mass transfer in multi-phase single particle systems. By
using a novel technique based upon the micropipette, the dissolution of liquid and
gas droplets in a liquid medium can be observed. Three classes of experimental systems
are observed: pure liquid droplet dissolution in a pure liquid environment, miscible
mixture liquid droplet dissolution in a pure liquid environment, and solute-containing
liquid droplet dissolution in a pure liquid environment. Experiments on the dissolution
of pure droplets of water in n-alcohols and n-alkanes showed that water droplets dissolved
ten times faster in the alcohols as compared to in the alkanes. When solubility was
taken into account, however, and diffusion coefficients calculated using the Epstein-Plesset
equation, diffusion constants for alkanes were twenty five times higher in alkanes
than for the corresponding alcohol (for example 12.5 vs 0.5 x 10-8 cm2/s for pentane
and pentanol). This difference in rates of diffusion of the single molecules reflects
the effect of hydrogen bonding on small solute diffusion, which is expounded upon
in Chapter 2.</p><p> A model for the dissolution of a droplet containing a mixture,
each component of which is soluble in the surrounding liquid medium is presented in
Chapter 3. The model is based upon a reduced surface area approximation and the assumption
of ideal homogenous mixing : Mass flux (dm_i)/dt=〖Afrac〗_i D_i (c_i-c_s){1/R+1/√(πD_i
t)}, where Afraci is the area fraction of component i, ci and cs are the initial and
saturation concentrations of the droplet material in the surrounding medium, respectively,
R is the radius of the droplet, t is time, and Di is the coefficient of diffusion
of component i in the surrounding medium. This model was tested for the dissolution
of ethyl acetate and butyl acetate in water and the dissolution of butyl acetate and
amyl acetate in water, and was found to provide a good fit. In Chapter 4, a partial
differential equation, R^2/D ├ ∂c/∂t┤|_η=(∝η)/D
∂c/∂η+(∂^2 c)/〖∂η〗^2 +2/η ∂c/∂η,
is presented for the dissolution of a solute containing droplet in a liquid medium,
and shell or bead formation is predicted. In Chapter 5, an application of the solute
containing droplet dissolution is presented in which suspensions of glassified protein
microspehres are used to improve the injectability of protein based pharmaceuticals.
Injectability is related to viscosity, and the viscosity of a suspension may be predicted
to follow the Krieger Dougherty equation: (η(Φ))/η_0 =(1-Φ/Φ_m
)^(-2.5Φ_m ) , where Φ is the volume fraction of the suspensate, η
is the viscosity of the overall suspension, η0 is the viscosity of the suspending
fluid, and Φm is the maximum possible volume fraction. Finally, in Chapter 6,
various experimental methods used to generate droplets are addressed.</p>
|
|
