The overall objective of this PhD thesis research is to understand and control phase separation in mixed perfluorinated fatty acid-phospholipid surfactant systems that have applications as pulmonary surfactant (PS) mixtures, with an ultimate view of controlling film composition, morphology and mechanical properties. In this context the interaction between perfluorooctadecanoic acid (C18F), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), the major component of native PS extract, and 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG) has been explored in Langmuir monolayers and Langmuir–Blodgett (LB) films using a combination of atomic force microscopy (AFM), fluorescence microscopy (FM) and Brewster angle microscopy (BAM) measurements. Thermodynamic and morphological studies of binary and ternary mixed films made of C18F, DPPC and DPPG indicated that both the phospholipids and C18F were miscible over a wide range of compositions. The mixed phospholipid-C18F films contained multimolecular aggregates that were highly enriched in the phospholipids. Furthermore, it was found that the magnitude of the DPPC-C18F interaction could be modulated by altering the concentration of sodium ions in the underlying subphase. Using a highly simplified lung mimic fluid (pH 7.4, 150mM NaCl), DPPC and C18F became fully immiscible. Moreover, the performance characteristics of the mixed films demonstrated the usefulness of C18F as an additive for PS formulations. The effectiveness of a PS protein mimicking peptide was evaluated against DPPC to allow comparison with previous measurements of DPPC-C18F mixed system. The mixing thermodynamics of the peptide and DPPC in Langmuir monolayer implied a repulsive interaction between the film components. The hysteresis response of the mixed monolayer films indicated that the lipid-protein mixture improved the re-spreading of DPPC films. Moreover, molecular-level organization of the mixed films explored by both FM and BAM confirmed the formation of liquid-expanded DPPC domains in the presence of minute amount of the peptide. In order to obtain a thorough understanding of the effect of the deposition process and surfactant tail polarities on the interfacial behavior of perfluorocarbon-hydrocarbon mixed monolayer films, both BAM and AFM measurements of arachidic acid (C20) with perfluorotetradecanoic acid (C14F) and palmitic acid (C16) with C18F mixed monolayer were performed. These measurements revealed that film morphology was minimally perturbed upon its deposition onto solid substrates. Coarse grained molecular dynamics (MD) simulations of films comprised of DPPC molecules with tails of various polarities suggested that the phase separation between the monolayer components could be controlled by varying surfactant tail polarities.

Indiana University-Purdue University Indianapolis (IUPUI) / The details of Polarization Modulation Near-Field Scanning Optical Microscopy (PM-NSOM) are presented. How to properly calibrate and align the system is also introduced. A measurement of Muscovite crystal is used to display the capabilities of the setup. Measurements of supported Lβʹ 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayers are presented, emphasizing how it was tooled in exploiting the anisotropic nature of the acyl chains. A discussion of how the effective retardance (ΔS = 2π( n_e-n_o )t/λ) and the direction of the projection of the acyl chains (θ) are measured simultaneously is given, (where t is the thickness of the bilayer and λ is the wavelength of light used). It is shown from ΔS the birefringence (ne-no) of the bilayer is determined, by assuming the acyl chain tilt with respect to the membrane's normal to be ϕ ≈ 32. Time varying experiments show lateral diffusions of ~ 2 x 10-12 cm2/s. Temperature controlled PM-NSOM is shown to be a viable way to determine the main phase transition temperature (Tm) for going from the gel Lβʹ to liquid disorder Lα state of supported DPPC bilayers. A change of ΔS ~ (3.8 +/- 0.3 mrad) at the main phase transition temperature Tm (≈41^o C) is observed. This agrees well with previous values of (ne-no) and translates to an assumed <ϕ> ~ 32^o when T < Tm and 0^o when T > Tm. Evidence of supper heating and supper cooling will be presented, along with a discussion of the fluctuations that occur around Tm. Finally it is shown how physical parameters such as the polarizability are extracted from the data. Values of the transverse (αt) and longitudinal (αl) polarizabilites of the acyl chains are shown to be, αt = 44.2 Å3 and αl = 94.4 Å3, which correspond well with the theoretical values of a single palmitic acid (C16) αt = 25.14 Å3 and αl = 45.8 Å3.

A température ambiante, la plupart des monocouches constituées de molécules formées de chaînes alcanes présentent des phases caractérisées par la rotation des chaînes autour de leur axe moléculaire. Afin d'obtenir un ordre cristallin, il est impératif de réduire l'énergie du système. De nouvelles sous-phases liquides utilisant des agents cryoprotectifs permettent d'accéder à des températures plus faibles que la température de glace de l'eau. Les monocouches de surfactants tels que les acides gras ou les phospholipides ont été préparées à volume et pression surfacique constants. L'étude de la stabilité des films par refroidissement a été effectuée par des isothermes de Langmuir et GIXOS et celle de l'ordre dans le plan par GIXD. Les molécules adoptent des phases cristallines qui sont induites par un processus d'autoassemblage d'origine exclusivement entropique et dont la densité de compactage est similaire à celle d'un monocristal à trois dimensions. La technique d'XPCS a enfin été employée pour relier la dynamique de surface du système étudié à la formation des phases cristallines.