The self-organization process of the porous anodic alumina (PAA) during hard anodization (HA) was proposed by synthetically investigating the nanopore morphology, the current density and barrier layer evolution of the PAA films, which were anodized in 0.3 M oxalic acid at 150 V (the voltage rising from 40 V to 150 V at the beginning). It was found that the high enough current density in the voltage rising stage can induce the fast film growth, which caused the pores to rapidly enlarge themselves and to reach a relatively ordered rearrangement. The barrier layer thickness showed linearly increase in voltage rising stage and then increased with a decelerated speed in the followed constant anodization stage, where the pores with growth advantage moved down straightly and gradually expanded their cell size to replace the inferior pores around. Accordingly, HA is a unequilibrium process and can be divided into two stages: I, the rapid pore enlargement and rearrangement during voltage rising stage, where the oxidation rate is larger than that of dissolution; II, competing growth of the nanopores during the followed constant voltage anodization, where the oxidation and dissolution rates approach to each other due to the thickened barrier layer. These findings are very helpful for more efficiently controlling the hard anodization process and developing new electrolyte systems to further broaden the interpore distance range.

•Miscibility and interactions between hexadecanol and DPPE were studied by Langmuir technology.•The thermodynamic parameters of the binary monolayer were analyzed based on the regular solution theory.•The two-dimensional phase diagrams were constructed.•The AFM observations of the monolayer strongly evidenced further the thermodynamic theory analysis.Hexadecanol is chemically stable and can be used as an effective addition in synthetic clinical lung surfactant preparations to improve their spreading properties. In this work, a detailed thermodynamic and structural characterization of a simple model system, which based on a hexadecanol-phospholipid mixture is reported. Langmuir monolayers of binary mixtures of hexadecanol/1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) have been studied with thermodynamic parameters and monolayer structure. The extent of the thermodynamic parameters has been evaluated by the direct related parameters, such as mean molecular area, percent of condensation, surface excess Gibbs free energies, isothermal compressibility, interaction energy parameter, activity coefficient and two-dimensional phase diagram. Monolayer film structure has been characterized by atomic force microscopy (AFM) technique. Combining thermodynamic and AFM data indicate that there exist repulsive and attractive interactions between the two film forming molecules and the binary films behave as non-ideal mixtures, which can be portrayed by the mole fraction of hexadecanol. At low mole fraction of hexadecanol, the monolayer is phase-separated and the interactions between hexadecanol and DPPE is more repulsive; while the content of hexadecanol up to 0.6, the monolayer becomes miscible and stable, the interaction between different molecules is more attractive. The addition of hexadecanol in the DPPE monolayer clearly affects the lateral organization of membranes and improves its surface tension kinetics. The results discussed in this context will be expected to be potential contribution for exogenous lung surfactant researches.Surface pressure-mean molecular area isotherms of hexadecanol/DPPE binary monolayers and their AFM images at mole fractions of Xhd = 0, 0.2, 0.4, 0.6, 0.8 and 1 (deposited surface pressure：35 mN/m, scanning range：5 μm × 5 μm).

The glycosylphosphatidyl inositol (GPI)-anchored proteins are localized on the outer of the plasma membrane and clustered in membrane microdomain known as lipid rafts. Among them, mammalian alkaline phosphatase (AP) is an enzyme widely distributed. So, it has important biological significance to study the combination of AP with lipid monolayer. In our work, the interaction between AP and sphingomyelin has been studied at the air-buffer interface as a biomimetic membrane system by the Langmuir film technique and atomic force microscopy. The surface pressure-area isotherm for the mixed alkaline phosphatase/sphingomyelin monolayer shown the presence of a transition from a liquid-expanded phase to the liquid-expanded/liquid-condensed coexist phase. And the surface compressional modulus suggested the mixed alkaline phosphatase/sphingomyelin monolayer has larger compressibility compared with the pure sphingomyelin monolayer. Besides, according to the micrographs, we inferred when combined with lipid monolayer at the air-buffer interface, the AP molecules formed polymer not multilayer or micelle. And, according to the limiting molecules area of AP, we inferred that 12 AP molecules formed a hexagon polymer unit.

Lipid rafts are of a dynamic microdomain structure found in recent years, enriched in sphingolipids, cholesterol and particular proteins. The change of structure and function of lipid rafts could result in many diseases. In this work, the monolayer behavior of mixed systems of D-sphingosine with cholesterol was investigated in terms of the mean surface area per molecule (Am), excess molecular area (ΔAex), surface excess Gibbs energy (ΔGex), interaction parameter (ω), activity coefficients (f1 and f2) as well as elasticity (Cs−1) of formed films. The deposited Langmuir-Blodgett (LB) monolayers were investigated with atomic force microscopy (AFM). Thermodynamic analysis indicates ΔAex and ΔGex in the binary systems with negative deviations from the ideal behavior, suggesting attractive interaction between molecules. The stability, elasticity and activity coefficients show a marked dependence on the mole faction of D-sphingosine. The results of observation by AFM show that the single D-sphingosine molecular film took on small granule structure. When mixing the D-sphingosine and cholesterol at different ratios, the mixed films transform from the chains structure to larger slice and net coexisting structure with the increasing of the cholesterol content. In the end, pure cholesterol forms more aggregated structure. AFM experiments effectively support the above findings and interpretation.

Sulfatides are important constituents of brain myelin membranes and it is thought to be involved in lateral domain formation in biological membranes. In this work, the interaction of mixed systems of sulfatide with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1, 2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), two of the major components in biological membranes, was investigated using the monolayer technique at the air–water interface. Based on the regular solution theory, the miscibility of the two binary systems in the mixed monolayer was evaluated in terms of mean surface area per molecule (Am), excess molecular area (ΔA(ex)), surface excess Gibbs energy (ΔG(ex)), interaction parameter (ω) as well as activity coefficients (f1 and f2) of formed films. Thermodynamic analysis indicates in the two binary systems with negative deviations from the ideal behavior. Accordingly, the values of the Gibbs energy of mixing, sulfatide-DPPC form stable mixtures at Xsul = 0.4 (Xsul is molar ratio of sulfatide in binary mixture) for all the selected pressures. As for sulfatide/DPPE system, at π = 5 and 30 mN m−1, the minimum for the Gibbs energy of mixing was found at Xsul = 0.6 and 0.2 respectively. But the minimum appeared at Xsul = 0.4 for other surface pressures. The activity coefficients (f1 and f2) of mixed monolayers were evaluated which show a marked dependence on the mole faction of sulfatide Xsul. AFM images could support the above findings as well as interpretation.

The monolayer properties of sulfatide and cholesterol binary system have been investigated with surface pressure–mean molecular area isotherms measurements and atomic force microscopy (AFM). The thermodynamic analysis indicates that the obtained negative deviation of the excess molecular area (ΔA(ex)) and surface excess Gibbs energy (ΔG(ex)) from the ideal behavior at various molar ratios, suggesting an attractive interaction between sulfatide and cholesterol in the monolayers as compared with the pure components monolayers. Meanwhile, the compression modulus (Cs−1) vs. surface pressure (π) and activity coefficients (f1 and f2) of mixed films dependencies for mixed monolayers are drawn at different mole fractions. The AFM images for the mixed sulfatide/cholesterol monolayers deposited on the mica at 15 and 30 mN m−1 show the stronger molecular attractive force to form condensed structure. The behavior of sulfatide is thought to be involved in lateral domain formation in biological membranes. Therefore, the interaction between sulfatide and cholesterol becomes more important in mimicking “lipid rafts” domains.