E. Ferroni

On the mechanism of collapse of arachidic acid films at the water/air interface

The importance of the study of the collapse phenomenon both for low molecular weight and macromolecular substances has been shown by several authors (1). I t is known and it has often been stressed that the collapse pressure and area strongly depend upon the rate and the modality of compression even for substances which are simple and very stable at the W/A interphase (2). Here we report a study on the collapse rates of a carboxylic acid at the W/A interphase, undertaken partially to ascertain the reproducibility conditions for the kinetics of substance separation from the monolayer, but chiefly to understand the mechanism and the energies of this process. Arachidic acid was selected for its great stability at the W/A interphase and also because it had previously been used by one of us in a study, at the same interphase, of its mixtures with a polypeptide (3). These components showed surface incompatibility. An understanding of the mechanism of the collapse of arachidic acid may be helpful in determining the reasons of such an incompatibility. Surface pressure measurements as a function of time were performed and ellipsometry was used mainly to obtain the thickness of the bidimensional layer at various stages of collapse. EXPERIMENTAL

Mono and multilayers of bivalent ion stearates

Abstract Monolayers and multilayers of stearic acid at the water/air interface on substrates containing Cu 2+ ions and Ba 2+ ions were studied. The spreading isotherms of the monolayers at 15, 20, 25 and 30°C and the corresponding two-dimensional equations of state and compressional moduli were determined. The thickness of the multilayers were determined ellipsometrically. The presence of both ions in these multilayers transferred from the substrate was determined by means of electron spectroscopy for chemical analysis (ESCA), scanning electron microscopy (SEM) and, for the CU 2+ ion, by means of electron spin resonance (ESR) spectroscopy. The results demonstrated that the transfer and the properties of Blodgett-Langmuir multilayers were very dependent on the monolayer properties. In particular, stable monolayers quantitatively transferred could be obtained only if the bidimensional phase was highly compressed.

On the mechanism of collapse of monolayers of macromolecular substances: poly(l, d, and dl)alanine

Abstract The collapse process of monolayers of poly( l , d , dl )alanine has been studied at the air—water interface, and on substrates containing Ca2+, Na+, and K+. It is demonstrated that the collapse process occurs in two stages. The first, attributable to a process of nucleation, is related to the detachment of the polymeric chains from the substrate; the second is controlled by a kinetic law of “zero order,” and can be attributed to the formation of a bilayer. Ellipsometric measurements confirm the presence of an average bilayer thickness in the collapsed film. Multiple internal reflection measurements on a germanium plate show that poly( l and d )alanine are present at the interface in the α-helix configuration, while with poly( dl )alanine, a considerable amount of the compound is present in the β configuration.

Thermodynamic properties of polymers in bidimensional layers

Abstract Monolayers of two samples of polypropylene containing grafted methyl acrylate branches have been studied at different temperatures. Spreading enthalpies and entropies were deduced by plotting values of surface pressure versus temperature at different values of the area. From the values of such thermodynamic properties we conclude that the macromolecules lie rigidly at the surface with considerable cohesive energy between the monomeric segments.

Structural analysis on the violet form of CoCl2 · 2 pyridine

Abstract An X-ray study has been performed by the Authors on the violet form of CoCl 2 · 2 Py . The atomic parameters have been determined by means of Patterson projections and electron density projections on the (001) and (010) planes. The structural data do not agree with the preceeding interpretations. In fact the structural analysis allows to establish that the complex is neither planar nor dimer. The results of this research are consistent with the definition of the compound as a pseudoctahedral and polinuclear complex. Such an interpretation may explain some physico-chemical properties of the complex. for istance the crystal growth and the colour of the solid compound and its solutions.

Bi- und tri-dimensional solutions of poly-vinyl-acetate

SummaryBidimensional films of PVA obtained, at air/water interphase, from different spreading solvents were studied: a) CHCl3 which is a “good” solvent, b) C6H6 which is an “intermediate” solvent, c) CH3OH which is a “poor” solvent.Both the coefficients of the bidimensional state equations of the “apparent” surface temperatureθ, converge to demonstrate that the processes of bulk solubilization and spreading are competitive; that is, if the spreading solvent is “poor”, the interphase behaves as a “good” solvent. The results have been confirmed by comparison with the Huggins Theory, as applied to monolayers, and by the spreading isotherms obtained for the same polymer on supports containing NaCl or CH3OH.ZusammenfassungEs werden die zweidimensionalen Filme des Polyvinylacetats (PVA) an Wasser/Luft-Grenzfläche studiert, unter Verwendung von verschiedenen Spreitungslbsemitteln: a) Chloroform (gutes Lösemittel), b) Benzol (mittleres Lösemittel), c) Methanol (armes Lösemittel). Die Koeffizienten der Gleichungen des zweidimensionalen Zustandes und die scheinbare Oberflächentemperatur zeigen, daß die Bulk-Löslichkeit und die Spreitfähigkeit in gewisser Weise miteinander verknüpft sind. Das heißt, daß, wenn das Spreitunglösemittel ein „armes” ist, die Grenzfläche sich als besseres Lösemittel benimmt. Die Ergebnisse, abgeleitet aus der Huggins-Theorie der Monoschichten und gefunden aus Spreitungsisothermen für die gleichen Polymeren mit Variation der Trägerflüssigkeit mittels Methanol und NaCI stehen in befriedigender Übereinstimmung.

Bidimensional mixtures of cholesterol and poly-γ-methyl-l-glutamate in α conformation at the water—air interface: mechanism of collapse

Abstract The mechanism of the collapse process of bidimensional mixtures of poly-γ-methyl- l -giutamate in α conformation and cholesterol was studied. It was shown that the collapse mechanism is described by a process of nucleation and growth. The Prout—Tompkins and the second-order kinetic laws were in agreement with the experimental data. The kinetic analysis of the collapse process confirmed the bidimensional immiscibility found in static conditions from the analysis of the thermodynamic parameters. Further information on the mechanism of collapse was obtained from the values of Δ G + , Δ H + , and Δ S + calculated applying the transition-state theory. Scanning electron microscopy supported the proposed nucleation mechanism and the bidimensional immiscibility of the components. Biological implications were also considered.

The graphon-polyelectrolytes interface as a model for coal slurries

Abstract The study of the adsorption mechanism of a series of aromatic polyelectrolytes from aqueous solutions of graphitized carbon black is reported. The interphasal distribution of a series of sodium salts of polynaphthalene sulphonates at the air/water interface was determined by a thermodynamic study. The adsorption film was found to be monomolecular at both interfaces, the polymers were oriented with the naphthalene rings nearly parallel to the interface. The above system was chosen to be the ideal representation of the solid/liquid interface present in actual slurries. Complementary zeta potential measurements on water/real coal mixtures support the results obtained on the model system. The study appears to be of particular relevance in estimating the slurriability of coals with different surface properties and in the selection of proper additives.

Mixed monolayers of polymethacrylic esters containing aromatic and aliphatic groups

The interfacial properties of mixtures of polymethacrylic polymers containing either aromatic or aliphatic side groups were studied at water-air interface in order to define the role of geometrical orientation on surface compatibility and the effect of aromatic interactions on ordered bidimensional systems. Two binary systems were studied: polyphenylmethacrylate/ polyhexylmethacrylate and polyphenylmethacrylate/polybenzylmethacrylate.Surface pressure and surface potential measurements were performed in the 288–303 K temperature range on the mixtures at different polymer concentrations. Further information was obtained from ellipsometric measurements and scanning electron microscopy of the collapsed material. The experimental results allow for the conclusion that both polymers containing aromatic groups are almost ideally miscible whereas mixtures of aliphatic and aromatic polymers are completely immiscible.

Monolayers and bilayers of lipids

Abstract The spreading monolayers of ceramides alone and in mixtures with monooleoyl glycerol were studied at the air/water interface in the 15-30°C temperature range. The bidimensional phases were determined from the spreading isotherms of the pure components, whereas the interfacial miscibility of the compounds being studied was deduced from the spreading isotherms of the mixtures. The specific resistance and capacitance of black lipid membranes containing mono-oleoyl glycerol and monooleoyl glycerol/ceramides in squalene were studied. Langmuir-Blodgett monolayers and bilayers obtained by the transfer of spreading monolayers at the air/water interface onto chromated glass slides, were prepared. Vesicles of dioleoylphosphatidylcholine and of mixtures of dioleoylphosphatidylcholine/ceramides were also prepared. The results obtained for the different types of aggregates were compared in order to find the relations that connect the characteristics of the various systems. Results showed that the possibility of obtaining flat and curved bilayers of pure components and of mixtures was closely connected to the phase of the corresponding monolayers at the air/water interface.