Marta Puggelli

Orientation and compatibility in monolayers: II. Mixtures of polymers

Abstract Pressure area isotherms at the water-air and water- n -hexane interfaces are reported for the following polymers: polymethylmethacrylate (PMMA), polyvinylacetate (PVA), polypropylmethacrylate (PPMA), polyvinylstearate (PVS), and polyoctadecylmethacrylate (POMA). The comparison of the experimental data with the bidimensional state equation deduced theoretically (Huggins equation) and ellipsometric measurements allows us to conclude that PMMA, PVA, and PPMA have, at the water-air interface, a “horizontal disposition,” while PVS and POMA have components that are “perpendicularly oriented” at the interface. The surface areas as a function of molar ratios, the “collapse pressure,” and the surface compressional modulus, for the bidimensional systems: PMMA-PPMA, PVS-POMA, PMMA-POMA, and PVA-PVS show the compatibility between macromolecules having the same orientation at the interface and the incompatibility between macromolecules having different orientation. The study of the water- n -hexane pressure area isotherms for the systems PMMA-PPMA and POMA-PVS shows that the main factor which determines the compatibility, at the water-air interface, is the interaction among hydrophobic chains.

Molecular interactions in mixed monolayers of polymers

Abstract The behavior of binary mixtures of poiy(methyl methacrylate) and poly(ethyl methacrylate) at the W/A interface has been studied and compared with the corresponding behavior of two pure polymers. The higher stability of the mixture at a 1/1 molar ratio with respect to the two pure polymers has been found from the compression isotherms and from the free energy of mixing values. Interchain cohesion energies have also been deduced; thus it is possible to attribute the higher stability to attraction forces between rigid segments.

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.

Monolayers of polyvinyl acetate

Abstract In order to compare the orientation and the energies of polyvinyl acetate at the interphase W A with the corresponding properties at the interphase W O , the spreading isotherms at the two interfaces are reported. From the comparison of virial coefficients of bidimensional state equations with those of equations theoretically deduced, and from the values of the thermodynamic spreading properties, we have demonstrated that at the interface W A the macromolecule lies as a deformed coil with moderate flexibility and with rather low attractive energies. In contrast, at the interphase W O the cohesion energies can be considered negligible.

Mixed monolayers of polymethyl methacrylate and polyethyl methacrylate at several temperatures

Abstract The behavior of mixtures of polymethyl methacrylate and polyethyl methacrylate in the bidimensional state at several temperatures is studied. The spreading isotherms are distinctly different at 30°C than at 20 and 25°C. At 30°C a first order transition between a gaseous state and a liquid state is present in all the spreading isotherms of the mixtures and of polyethyl methacrylate alone, except for mixtures having a 1 1 molar ratio. This mixture which is the most stable even at low temperature, can be considered to be a mixture having characteristic surface properties and high spreading entropy and enthalpy values.

Behavior of vinyl polymers in mixed monolayers

Experiments were done on mixed monolayers of polyvinylacetate (PVA) with polymethylmethacrylate (PMMA) and with polyvinylbutyrate (PVB) at the water/air interface at 25°C. The results show that PVA yields ideal bidimensional solutions with PMMA, as previously found, and nonideal solutions with PVB. From the comparison among the corresponding bidimensional state parameters, and, in particular, the spreading thermodynamic functions of the three polymers, it appears that the different behaviors of mixtures may be attributed to the greater polymer-substrate interactions of PVB with respect to PMMA.

Enzymatic hydrolysis reaction of phospholipids in monolayers

Abstract The hydrolysis reaction of l- , d- and d , l -dipalmitoylphosphatidylcholine (DPPC) catalized by bee venom phospholipase A 2 was studied in spreading monolayer at the water/air interface. DPPC and the hydrolysis products, palmitic acid and l -lysophosphatidylcholine, palmitoyl were characterized at the interface by means of surface pressure, surface potential and ellipsometric measurements. Furthermore, mixed monolayers of reagents and products were investigated to ascertain their miscibility. The results show that the hydrolysis reaction can be followed by the decrease of surface pressure with time on subphases containing β-cyclodextrin, a well-known complexing agent of many amphiphilic compounds. The order of the reaction, the kinetic constant and other kinetic parameters are deduced.

Spectroscopic investigation of tetracycline interaction with phospholipid Langmuir–Blodgett films

Abstract A widely used veterinary antibiotic, tetracycline (TC), has been incorporated in Langmuir–Blodgett (LB) films of dipalmitoylphosphatidic acid (DPPA) by means of two different procedures: co-transfer and incubation in solution. The resulting structures were characterized by means of contact angle and ellipsometric measurements. The presence of the antibiotic in the phospholipid film was evidenced by means of UV–Vis electronic absorption and infrared vibrational spectroscopy. The two sets of measurements unambiguously indicated the presence of the drug in the LB layer films obtained with both methods, although incubation led to a smaller content of immobilized tetracycline. In both cases, the drug was found to reside in the hydrophilic portion of the layers due to specific interactions of the dimethylamino group of the molecule with the polar head groups of the phospholipid.

Langmuir-Blodgett monolayers and multilayers of stearic acid and stearyl amine

Abstract For mixed monolayers it has long been shown that the addition of stearic acid facilitates the transfer of Langmuir-Blodgett monolayers and multilayers otherwise difficult to transfer. Mixed monolayers of stearic acid (SA) and stearyl amine (SAM) have been studied with the aim both of obtaining monolayers appropriate for transfer and of defining the parameters relevant to the latter. The spreading isotherms of SA and SAm in several molar ratios on a subphase at pH 5.5 and T = 20°C allowed determination of the complete miscibility of the two components. Moreover the comparison of the transfer ratios between the mixtures and the pure components proves that the mixtures, and in particular the equimolecular mixture, show an improved transferability. The hysteresis isotherms show that the improved transferability can be attributed to improved surface rheological properties of SAm monolayer to which SA had been added. The Fourier transform IR spectra of transferred multilayers and the spectra of the monolayer of each component and of their mixtures in equimolecular ratio obtained by electron spectroscopy for chemical analysis show that, beyond the favourable disposition of the hydrophobic chains, interactions between the carboxilic and aminic functional groups are responsible for the improved transferability.

Bidimensional mixtures of polymethylmethacrylate with fatty esters at water-air interface

Two-dimensional mixtures were studied between a polymer, polymethylmethacrylate (PMMA) which has at the water-air interface its chains distributed almost parallel to that interface, and two esters, methylstearate (MS) and methyloleate (MO), characterized by having the same chain length but a different interface orientation.It was shown that the main interactions occurring are those between the hydrophobic chains, and consequently that compatibility between the substances depends essentially on their having the same interface orientation.