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The paper presents a detailed characterization of stearic acid film in various experimental conditions, recorded both in the pre- and post-collapse region, using – in addition to π–Α isotherms – visualization of film structure and thickness measurements (using Brewster angle microscope, BAM) supplemented with a precise analysis of compressibility modulus versus area (C s −1- A) plots. π–Α isotherms recorded for unionized molecules exhibit a liquid-condensed (LC) state where the thickness (th) and the compressibility modulus (C s −1) remain constant with monolayer compression along a plateau region, where a tilt angle of 73.5°, in respect to the water surface, was calculated for stearic acid molecule. Films subjected to subsequent compressions (beyond the collapse) and expansions show semi-reversible behavior as proved with BAM images. Upon the increase of carboxylic group ionization in alkaline pHs and increasing the speed of compression, the "spike" at the collapse changed its shape from sharp to rounded. Upon further compression, a long plateau transition has been observed. Within this post-collapse plateau, a three-fold increase in film thickness was observed, confirming the previously suggested model of trilayer formation. However, the visualization of film structure with BAM revealed that this process does not occur homogeneously, but through the nucleation of trilayer structures in the form of domains that undergo a continuous process of growth and coalescence within the post-collapse plateau region. The application of the adapted Clausius-Clapeyron equation indicates that the process of trilayer formation is endothermic and implies an increase of entropy, which has been additionally proven by PM-IRRAS. [Display omitted] • Full characteristics of stearic acid (SA) film in pre- and post-collapse region is presented. • Film thickness measurements proved a tilt orientation of 73.5° for SA in LC phase. • A change in "spike" shape at π c results from increased ionization and compression speed. • A long plateau transition beyond π c was observed. • Post-collapse transition implies an increase in entropy as proved with PM-IRRAS. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Oxysterols, which are products of cholesterol oxidation, are important biological molecules. For our investigations we have selected two epimers: 7α-hydroxycholesterol (7α-OH) and 7 β-hydroxycholesterol (7β-OH). Both molecules have been found to be capable of stable Langmuir monolayer formation, however, the characteristic of their monolayers were quite different. Contrary to 7β -OH, which isotherm devoid any transition, the π/A dependence for 7α-OH displayed a broad plateau. Temperature strongly affected this plateau transition – the lower the temperature, the higher the surface pressure of the transition. Such an inverse temperature dependence is uncommon for classical film-forming molecules. Film thickness results excluded multilayers as the probable cause for this plateau. Based on theoretical calculations it was possible to infer that the plateau can be attributed to the change of orientation upon film compression, from being anchored mainly with both polar groups in the pre-plateau region to that with one polar group being detached from the water surface in the post-plateau region. Differences in surface behavior of both diastereoisomers have been explained as being due to orientation of OH groups in their molecules; i.e. for 7β-OH both hydroxyl groups (at C3 and C7) are situated on the same side of the rings A and B, while for 7α-OH – on different sides, which induces the lifting off of one OH group from the water surface. [ABSTRACT FROM AUTHOR]

Mixed-metal oxides exhibit novel properties that are not present in their isolated constituent metal oxides and play a significant role in heterogeneous catalysis. In this study, a titanium-copper mixed-oxide (TiCuO x ) film has been synthesized on Cu(1 1 1) and characterized by complementary experimental and theoretical methods. At sub-monolayer coverages of titanium, a Cu 2 O-like phase coexists with TiCuO x and TiO x domains. When the mixed-oxide surface is exposed at elevated temperatures (600–650 K) to oxygen, the formation of a well-ordered TiCuO x film occurs. Stepwise oxidation of TiCuO x shows that the formation of the mixed-oxide is faster than that of pure Cu 2 O. As the Ti coverage increases, Ti-rich islands (TiO x ) form. The adsorption of CO has been used to probe the exposed surface sites on the TiO x –CuO x system, indicating the existence of a new Cu + adsorption site that is not present on Cu 2 O/Cu(1 1 1). Adsorption of CO on Cu + sites of TiCuO x is thermally more stable than on Cu(1 1 1), Cu 2 O/Cu(1 1 1) or TiO 2 (1 1 0). The Cu + sites in TiCuO x domains are stable under both reducing and oxidizing conditions whereas the Cu 2 O domains present on sub-monolayer loads of Ti can be reduced or oxidized under mild conditions. The results presented here demonstrate novel properties of TiCuO x films, which are not present on Cu(1 1 1), Cu 2 O/Cu(1 1 1), or TiO 2 (1 1 0), and highlight the importance of the preparation and characterization of well-defined mixed-metal oxides in order to understand fundamental processes that could guide the design of new materials. [ABSTRACT FROM AUTHOR]