Ashis Shil

Adsorption of a cationic water-soluble dye onto cationic Langmuir-Blodgett films via nano clay platelets: An efficient approach to control the H-dimer

ABSTRACT This communication reports the successful adsorption of a water-soluble cationic fluorescent dye Acridine Orange (AO) onto Langmuir–Blodgett (LB) films of a cationic amphiphile octadecylamine (ODA) in the presence of nano-clay platelets hectorite. Acridine orange (AO) has been widely used as a stainer for the characterization of biopolymers. But AO has a tendency to form non-florescent H-dimer even in the aqueous solution. Anionic nano-clay platelets hectorite played an important role in controlling the H-dimer formation of AO in the hybrid film. Effects of various parameters in the adsorption process were investigated in detail.

Formation of J-aggregates in Langmuir-Blodgett films: Effect of stearic acid and nano clay platelets

ABSTRACT In the present communication, a water soluble prophyrin derivative, tetra-cationic dye 5, 10, 15, 20-tetrakis (1-methyl-4-pyrindino) porphyrin tetra (p-toluenesulfonate) (abbreviated as TMPyP) has been used to prepare stable Langmuir monolayer at the air–water interface by allowing it to adsorb from the aqueous subphase, into the preformed Langmuir monolayer of anionic stearic acid (SA) and cationic octadecylamine (ODA). Anionic nano clay platelets Laponite acted as mediator to initiate adsorption of cationic TMPyP into the cationic ODA monolayer. Surface pressure versus area per molecule (π-A) isotherm studies of SA-TMPyP complex monolayer gave valuable information about the TMPyP molecular area. Organizations of TMPyP molecules were greatly affected in the two different kinds of anionic and cationic matrices. Adsorption led to the flattening of TMPyP molecules in both the matrices. The organization of TMPyP tagged nano clay platelets in preferred direction led to the development of J-band resulting due to the formation J-aggregates in the Langmuir-Blodgett (LB) films. This has been confirmed by UV-vis absorption spectroscopic studies.

Metal ion-induced H-aggregation of a water-soluble anionic dye Congo red (CR) in Langmuir–Blodgett (LB) film

Abstract Present communication reports the preparation of Langmuir monolayer of water-soluble anionic dye Congo red (CR) by allowing it to adsorb from the aqueous subphase onto the preformed Langmuir monolayer of anionic stearic acid using divalent metal cations Mg2+ as mediator. Isotherm and compressibility studies of SA-Mg-CR hybrid monolayer gave valuable information about the molecular organisation in the Langmuir monolayer. Absorption spectroscopic studies revealed the formation of H-aggregates in the hybrid Langmuir–Blodgett (LB) films fabricated at lower salt concentration in the subphase. Atomic Force Microscopic image gave visual evidence of distinct nanocrystalline domains in the LB monolayer film.