Pulmonary surfactant protein C containing lipid films at the air-water interface as a model for the surface of lung alveoli.

The pulmonary surfactant lines as a complex monolayer of lipids and proteins the alveolar epithelial surface. The monolayer dynamically adapts the surface tension of this interface to the varying surface areas during inhalation and exhalation. Its presence in the alveoli is thus a prerequisite for a proper lung function. The lipid moiety represents about 90% of the surfactant and contains mainly dipalmitoylphosphatidylcholine (DPPC) and phosphatidylglycerol (PG). The surfactant proteins involved in the surface tension adaption are called SP-A, SP-B and SP-C. The aim of the present investigation is to analyse the properties of monolayer films made from pure SP-C and from mixtures of DPPC, DP…

Real-time microfluorescence studies of Langmuir-Blodgett deposition: Monolayer adsorption and desorption

Abstract Observations of the meniscus region in a typical Langmuir-Blodgett configuration are obtained using fluorescence microscopy. Studies of the meniscus position as a function of pH demonstrate that the meniscus height increases upon charging the monolayer owing to the repulsive interaction between monolayer and substrate surfaces. Through the correspondence between meniscus height and contact angle the adhesion forces between monolayer and substrate as a function of monolayer charge are assessed. The phenomenon of desorption upon resubmerging a deposited film is described and it is shown that the meniscus height at the onset of the desorption is greater for higher pH.

Colloids and interfaces in bochum

On the Electrostatic Component of the Adhesional Interaction between Solid Substrates and Langmuir Monolayers

The work of adhesion between Langmuir monolayers and solid surfaces in a hydrophilic Langmuir-Blodgett configuration has been measured as function of the surface charge densities σ of the contacting surfaces. It was derived from the equilibrium meniscus height which was measured with the transfer fluorescence microscope. The surface charge density of the contacting surfaces was varied by changing the subphase pH. With both surfaces negatively charged (dimyristoylphosphatidylethanolamine onto SiO2-substrates) and low charge densities (σ < 1 e−/100 A2)) we observe a decrease of the adhesion with increasing charge density. At high charge densities (dimyristoylphosphatidic acid onto SiO2-substr…

Molecular adhesion interactions between Langmuir monolayers and solid substrates

Abstract Substrate-monolayer adhesion interactions between differently prepared SiO2 surfaces and Langmuir monolayers were investigated. From the relation between the contact angle and the surface tension of a Langmuir monolayer in the configuration of Langmuir wetting the work of adhesion between the substrate and the monolayer as a function of the molecular packing and the transfer ratios was determined. Thus the molecular work of adhesion of different SiO2-dimyristoylphosphatidylethanolamine surfaces was quantified. The relation between the local adhesion interactions and the molecular packing and structure is presented and substrate-induced phase transitions are discussed.

Structural Relationships between Floating and Deposited Monolayers of Docosanoic Acid

Floating docosanoic acid (behenic acid) monolayers in the SmI and SmH phase were deposited with the Langmuir-Blodgett technique onto thin polymethylmethacrylate (PMMA) and Formvar substrates and investigated by electron diffraction. The molecular packing of the monolayers on the substrates vary from those on the water surface and are different for different substrates. On PMMA four phases (H, SmB, SmI, SmL) have been identified, depending on the deposition conditions. While SmB and SmI are known for docosanoic acid on the water surface, H and SmL have only been unequivocally observed in other substances or on other subphases. The monolayer structure on Formvar was identical under all deposi…

Fluorescence Microscopy Studies of Structure Formation in Surfactant Monolayers

Monolayers of water-insoluble surfactants (Langmuir monolayers) are important model system in basic research for studying the self-organization of organic molecules into two-dimensional layers [1, 2]. These floating films are also the basis for the build-up of complex multilayered structures on solid substrates, so-called Langmuir—Blodgett films (LB-films), which are of considerable interest in fundamental science and promise some future practical applications [3].

Orientational order of Langmuir–Blodgett films as determined by fluorescence anisotropy

The orientational order parameters 〈P2〉 and 〈P4〉, of cadmium stearate Langmuir–Blodgett multilayers have been calculated from steady state fluorescence anisotropy experiments. It has been shown that it is valid to model the polarization components using the assumptions that the fluorescent probes are axially symmetric, the film is azimuthally symmetric within the plane, and that the rotational motion is slow enough to be neglected. Although the data do not preclude a dependence of anisotropy on thickness, within the sample‐to‐sample variations, there is no significant effect of thickness on orientational order. The order parameters for newly deposited films are 〈P2〉=0.33 and 〈P4〉=0.02. The …

Surface properties of valine-gramicidin A at the air-water interface

Abstract Fluorescence microscopy, X-ray reflectivity and ellipsometry have been applied to the study of a monolayer of valine-gramicidin A (VGA) at the air-water interface to obtain insight into the conformation and orientation of VGA, and to clarify the shoulder observed in its π - A curve (12.5–16 mN m −1 , 240 – 175 A 2 molecule −1 ). At low molecular areas, the X-ray reflectivities are consistent with formation of a single layer of tubular-shaped dimers. Fluorescence microscopy yielded homogeneous pictures suggesting that on the macroscopic scale the shoulder cannot be attributed to domain formation. Thicknesses calculated from the ellipsometric isotherm are consistent with the X-ray da…

Ellipsometric studies of behenic acid at the air-water interface

The rich phase behaviour of monolayers of behenic acid (=docosanoic acid) has been analyzed by null ellipsometry in isothermic and isobaric measurements. By using structural data known from x-ray measurements the anisotropy and refractive indices in the vicinity of the S-CS phase transition have been calculated with a minimum of model assumptions. The calculated values are: nsx=1.47. ncsx=1.48. nsz=1.54. ncsz=1.55. and anisotropy γ=nx/nz ≈0.95. It is also shown that ellipsometry is a very sensitive and convenient method of detecting phase transitions. Its value for quantifying the roughness of the monolayer in the close vicinity of phase transitions due to thickness and density fluctuations…

On-Line Structure Control of Langmuir-Blodgett Films

Studies of monolayer/substrate adhesion as function of the monolayer headgroup charge: DMPE and DMPA

The variation of the work of adhesion between lipid monolayers and a plane silicon oxide surface in a typical LB-configuration is measured as function of the subphase pH. The adhesion energy is deduced via fluorescence microscopy from the equilibrium meniscus height. With increasing pH the negative headgroup charge of both, dimyristoylphosphatidylethanolamine (DMPE) and dimyristoylphosphatidic acid (DMPA) monolayers increases. The increasing charge of DMPE is reflected in a measured decrease of the work of adhesion at higher pH. The DMPA/SiO2 interaction is not affected by increasing headgroup charges. These results are qualitatively understood in terms of an electrostatic double layer inte…

Thermostability of polymeric langmuir-blodgett films

Fluorescence microscopy studies of layer/substrate interaction during the Langmuir-Blodgett transfer: Fractional condensation and local layer modification in lipid monolayers at the three-phase line

Transfer fluorescence microscopy reveals the substrate-mediated fractional condensation and phase-selective deposition of dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylethanolamine (DMPE) monolayers during the LB-transfer. Preferentially the higher ordered liquid-condensed (LC) state is transferred onto the substrate during the transfer of a monolayer in the LC/LE (liquid/expanded) coexistence state on the water subphase. This is manifested in the directly observable attraction of LC-domains towards the three-phase line and observation of a domain-free gap as consequence of the segregation of the fluorescent probe into the floating monolayer adjacent to the three-phase li…

Physisorption Instabilities during Dynamic Langmuir Wetting

Continuous dynamic Langmuir wetting of lipid monolayers can create regular stripe patterns on the solid substrate surface. Monolayers doped with minor amounts of fluorescence dye may be deposited in stripes of alternating high and low dye concentration. In case of pure monolayers stripes are observed with AFM. The striations run normal to the dipping direction and have widths of typically several micrometres and distances varying from 1 to ≈ 100 μm. The stripe widths, distances, and fluorescence contrast depend on deposition speed, surface pressure, substrate surface preparation, and dye concentration. The patterns probably result from physisorption (meniscus) instabilities caused by a feed…