Effects of dispersion state and surface composition on the dynamic surface tension behavior of sparingly soluble or insoluble surfactant systems
Abstract
The dynamic surface tension behavior of aqueous dispersions and the spread monolayer behavior of dipalmitoylphosphatidylcholine (DPPC), hexadecanol, surfactant protein SP-C, and their mixtures were investigated as model systems for sparingly soluble or insoluble surfactants and also as representative systems for commercial lung surfactant replacement drugs. The composition and microstructure of monolayers were investigated with FTIR-ATR spectroscopy. The phase behavior and microstructures of dispersed crystallites were studied with DSC, XRD, SEM, and FTIR spectroscopy. The dispersed surfactant particles are shown to participate and play key roles in the dynamic adsorption as both a source of molecules to the surface and a depository of molecules from the surface. For hexadecanol particles, the controlling mechanism for adsorption dynamics appears to be the dissolution of particles in the bulk, followed by molecular diffusion and adsorption to the air/water interface. The preparation protocols affect the particle size and microstructures, and thus the dissolution, diffusion, and adsorption rates. The surface tension minima under pulsating area conditions are lower than the equilibrium tensions because of adsorption hysteresis, where extra molecules adsorb during area expansion and increase the surface density beyond the equilibrium during the ensuing area compression. Binary mixtures of DPPC with hexadecanol, or DPPC with SP-C, show interesting and strong synergistic effects in lowering the surface tension. The monolayer collapse pressure increases over the collapse pressures of single components. The surface tension maxima or the minima under pulsating area conditions are quite lower than those for pure dispersions. As the surface area and density change, so do the dynamic surface compositions. The surface composition studies after surface compression indicate that hexadecanol is partially excluded (but SP-C seems to be favored) relatively to DPPC. The results are compared with results from the commercial lung surfactant replacement drugs. It is concluded that the ability of DPPC for decreasing the dynamic tensions is enhanced considerably by the presence of one or more secondary components. The results have important implications for understanding the behavior of lung surfactants for devising simpler formulations with comparable dynamic surface behavior, and for other application areas such as foaming and coating flows.
Degree
Ph.D.
Advisors
Franses, Purdue University.
Subject Area
Chemical engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.