Thermodynamics and mass transfer in nonhomogeneous mixtures

• Main Author: Kosto, Timothy James
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2003
• Subjects: Chemical engineering
• ISBN: 049636247X; 9780496362479

This study investigated the application of principles and processes from polymer thermodynamics and mass transfer to problems in biotechnology and nanotechnology. Specifically, solution thermodynamics in confined pores, controlled release diffusion modeling and the manufacture of biologically-active, sustained-release tissue engineering scaffolds were explored. Solution behavior in nanopores was studied using equilibrium thermodynamics to predict the concentration profile in a confined, open domain. Partition coefficients exceeding 109 were predicted using thermodynamic arguments and the calculus of variations. Critical wetting transitions characteristic of heterogeneous mixtures were observed. A drug release model based on the modified Cahn-Hilliard equation was used to predict both the diffusional and the ripening exponents in dispersed systems that are losing mass. This model was consistent with Fickian behavior with respect to flux out of the system. The ripening exponent for dispersed, sustained release systems increased from ⅓ for bulk ripening to ⅔ in mass release systems; smaller particles near the depleted zone are removed by mass loss, increasing the average particle radius. Compositional quenching, previously used in the manufacture of impact modified polymer blends, was applied to systems of biological significance. A model enzyme, α-chymotrypsin, was incorporated into low-density polyethylene, polystyrene and ploy(lactide-co-glycolide). Four different process techniques were investigated: three devolatilization schemes and one freeze drying scheme. Composites made from LDPE and polystyrene were suitable for applications in heterogeneous biocatalysis; PLGA based materials were designed as sustained release tissue engineering scaffolds. Biocatalytic materials made from LDPE exhibited leaching behavior and limited activity in aqueous systems. In organic transformations, they exhibited more than fifty times the activity of suspended enzyme. Leaching behavior was caused by large enzyme particle sizes (∼26μm) that resulted from process restrictions. The manufacture of PLGA composites by either flash freezing or a batch devolatilization process was investigated. Although both process alternatives produced low particle size composites (<5μm), materials made by devolatilization exhibited greater activity retention over time and demonstrated sustained release of the entrapped enzyme for more than four weeks.