Spinodal decomposition in multicomponent fluid mixtures: A molecular dynamics study

A density-functional model for controlled release

Polymer diffusion based on density-functional theory is applied to controlled release systems. These models explicitly treat the multiphase characteristics of biomolecule-polymer composites typical of drug delivery devices. Polymer diffusion was modeled using the modified Cahn-Hilliard equation with periodic boundary conditions in one dimension and near-zero concentration boundaries in the second dimension. The diffusional driving forces are differences in chemical potential based in part on the Flory-Huggins free energy of mixing in polymer systems rather than concentration gradients. Release rates from this model were compared to exponential models typically used in the drug delivery literature. Simulations based on this model showed that the diffusional exponent is 1/2; this exponent is consistent with Fickian models at early times. Particle growth, which also occurs in diffusing, dispersed systems, was observed. The particle growth exponent in these systems was 2/3, twice the value typical in bulk ripening systems. The increased growth rate was caused by the elimination of small particles due to diffusion out of the system, which removed the low particle size region of the distribution faster than ripening alone.

Domain growth in ternary fluids: A level set approach

We analyze phase separation in ternary systems in the asymptotic hydrodynamic regime when the volume fractions and concentrations are constant. The multiphase Navier-Stokes equations are solved using a level set method. A new projection method was developed to treat multiple junctions for systems with more than two phases. It is found that surface tension ratios can alter the growth mechanism of a minority phase in the presence of two majority phases. When the minority phase wets the interface of the majority phases the domain growth rate of all three phases is initially similar to that of a symmetric binary fluid but slows down at later times.