Subrata Deb

Formation of Complex Langmuir and Langmuir-Blodgett Films of DNA with a Dichain Cationic Surfactant

Formation of complex monolayers between a dichain cationic surfactant, namely, dihexadecyldimethylammonium bromide (DHDAB) and deoxyribonucleic acid (DNA) at the air-water interface was first time systematically investigated here. The adsorption of DNA onto DHDAB monolayer was monitored by observing the surface pressure vs. time graph. The polyion-complex monolayers formed in situ through the electrostatic attraction between cationic DHDAB and the phosphate groups of anionic DNA. The organization of the DNA-DHDAB complex at the air-water interface deduced from surface pressure-area (π-A) isotherms was compared with the spectroscopic data in Langmuir-Blodgett films. Study of UV-Vis absorption spectra of pure DNA solution and DNA adsorbed DHDAB complex Langmuir-Blodgett films confirms the successful transfer of the films onto quartz substrates.

Adsorption of Chicago Sky Blue on the Langmuir Monolayer and Langmuir-Blodgett Films of Octadecylamine

This paper reports the incorporation of an inhibitor of Human Immunodeficiency Virus (HIV), viz. Chicago Sky Blue (CSB) dye within an insoluble cationic octadecylamine (ODA) Langmuir monolayer. A surface pressure-area isotherm study confirmed the strong interaction between long chain amine and CSB dye. At higher surface pressure, CSB molecules tend to squeeze out from the octadecylamine monolayer. SEM study confirms this observation. Adsorption kinetics shows that the amount of dye adsorbed depends on the concentration of the dye present in the subphase. It was observed that the absorption process mainly occurred due to the electrostatic interaction between the cationic amino group of long chain amine and the sulphonate group of CSB dye. UV-Vis absorption spectroscopic study indicates the formation of aggregates of CSB dye in the mixed (ODA-CSB) LB films.

An Investigation of the Behavior of Binary Mixed Langmuir Monolayer of 2,2′-p-Phenylenebis (5-phenyloxazol) and Arachidic Acid

A systematic study is reported on the monolayer characteristics of 2,2′-p-phenylenebis (5-phenyloxazol) (POPOP) mixed with arachidic acid (AA) at the air-water interface, using surface pressure versus area per molecule (π-A) isotherms complemented with absorption spectroscopy as well as scanning electron microscopy. The (π-A) isotherms of POPOP mixed with AA at different mole fractions show a plateau like region at very low surface pressure, which suggests a phase transition corresponding to a reorientation of the POPOP molecules at the air-water interface. The mixing behavior was obtained from surface pressure-area isotherms by using the surface phase rule and excess area criterion. Results show that POPOP is immiscible in AA, leading to the formation of aggregates. These observations are confirmed by ultraviolet-visible absorption spectroscopy and scanning electron microscopy. Absorption spectra of the mixed LB films reveal that I-type of aggregates play their prominent role in the mixed LB films.

Incorporation of Erythrosin B Within the Restricted Geometry of Langmuir Monolayer and Langmuir-Blodgett Films of Octadecylamine

This paper reports the monolayer characteristics of cationic octadecylamine (ODA) on both distilled water and aqueous Erythrosine B (EB) dye solution at the air-water interface. From the pressure-area isotherms at various pHs, EB anions in the subphase were found to interact with the insoluble monolayer of cationic octadecylamine (ODA). Adsorption kinetics shows that the amount of dye adsorbed depends on the concentration of the dye present in the subphase. It was observed that the adsorption process mainly occurred due to the electrostatic interaction between the cationic amino group of long chain amine and the anionic part of EB. The spectroscopic characteristics of the mixed LB films, solution, have been compared using UV-vis absorption and fluorescence spectroscopic data. These studies indicate the formation of aggregates in the thin films. Scanning electron microscopic study certainly confirms the presence of aggregates of EB dye in the (ODA-EB) mixed LB films.

COMPARATIVE STUDY OF THE BEHAVIOR OF BATHOPHENANTHROLINE IN THE RESTRICTED GEOMETRY OF LANGMUIR–BLODGETT FILM WITH TWO DIFFERENT FATTY ACIDS

This communication reports the successful fabrication and the comparative study of Langmuir and Langmuir–Blodgett (LB) films of nonamphiphilic phenanthrene derivative, 1, 10 phenanthroline (bathophenanthroline) (BATH), when incorporated to a long chain fatty acid viz. heptadecanoic acid and stearic acid. Measurements of compressibility modulus from the surface pressure versus area per molecule isotherm indicate that the mixed film of BATH and SA is harder than that with HA. The plot of area per molecule versus mole fraction is the indication of some repulsive interactions between binary components of the mixed monolayer which facilitates the formation of aggregates. UV–Vis absorption spectroscopy and steady-state fluorescence spectroscopy confirms the formation of microcrystalline aggregates in the mixed LB films. Scanning electron microscopic study supports this observation. The dependence of various LB parameters in the mixed films such as mole fraction, number of layers and surface pressure of lifting have also been investigated in the light of electronic absorption spectroscopy.

Formation and Characterization of Anionic Dye–Polycation Molecular Films by Layer-by-Layer Adsorption Process

Monolayer and multilayer films were formed by electrostatic self-assembly of poly (allyl amine) hydrochloride (PAH) and a strong fluorescent dye eosin Y (EY). In agreement with other published results, these compounds were found to form high-quality, closely packed monolayer and multilayer onto quartz substrate. The films formed on quartz substrate were then characterized in light of UV-Visible (UV-Vis) absorption spectroscopy and scanning electron microscopic (SEM) methods. Molecular movements were found to persist in the recently lifted layer-by-layer (LBL) films and about 72 h were required to get the film in stable condition. The photophysical characteristics of LBL films were found to vary with various parameters, such as number of deposited layers, dipping time in dye solution, pH of the PAH solution, and concentration of the dye. Both UV-Vis absorption spectroscopy and SEM studies also revealed the formation of molecular aggregates in the films.

Phase separation in the Langmuir–Blodgett films of p-quaterphenyl mixed with two different matrices

The phase behavior of two components p-quaterphenyl (QP) and polymethyl methacrylate (PMMA)/heptadecanoic acid (HA)) in the Langmuir monolayer was characterized. The surface pressure versus area per molecule isotherms revealed that the area per molecule systematically changed with increasing mole fractions of QP, indicating that repulsive types of interactions were involved between the QP and the matrix molecules (PMMA/HA), leading to the phase separation which in turn stimulated the aggregate formation. Absorption spectroscopy, complemented with scanning electron microscopy (SEM), confirmed the aggregation of QP molecules in the mixed films.