Role of microenvironment in the mixed Langmuir–Blodgett films

This paper reports the π–A isotherms and spectroscopic characteristics of mixed Langmuir and Langmuir–Blodgett (LB) films of nonamphiphilic carbazole (CA) molecules mixed with polymethyl methacrylate (PMMA) and stearic acid (SA). π–A isotherm studies of mixed monolayer as well as the remarkable change in collapse pressure of the mixed monolayer isotherms definitely show that CA is incorporated into PMMA and SA matrices. However, CA is stacked in the PMMA/SA chains and forms microcrystalline aggregates, as is evidenced from the scanning electron micrograph picture. The nature of these aggregated species in the mixed LB films has been revealed by UV–vis absorption and fluorescence spectroscopic studies. The presence of two different kinds of band systems in the fluorescence spectra of the mixed LB films have been observed. This may be due to the formation of low-dimensional aggregates in the mixed LB films. Intensity distribution of different band systems is highly sensitive to the microenvironment of two different matrices as well as also on the film thickness.

Figure shows a scanning electron micrograph (SEM) of the 10-layer mixed LB film of 0.5 M of CA in SA matrix. The aggregates with sharp and distinct edges correspond to the three-dimensional aggregates of CA in LB films. The smooth background corresponds to the PMMA matrix. The formation of distinct crystalline domains of CA, as evidenced from the SEM, provides compelling visual evidence of aggregation of CA in the LB films.Figure optionsDownload as PowerPoint slide