Brewster Angle Microscope – An Excellent Tool for Nanoscience Researchers

Abstract

An indigenous development of Brewster Angle Microscope (BAM) is completed at National Chemical Laboratory (NCL), India that is real time imaging instrument capable of imaging the monolayer while compressing the barrier trough simultaneously. The instrument will be useful for the basic research in the area of nanoscience. BAM has proven to be an excellent tool for the characterization of the morphology of insoluble monolayers of the surfactant molecules at air‐water interface, which are known as Langmuir films. BAM technique that was developed more than a decade ago globally, is well‐known optical method for visualizing extremely thin films. BAM can reveal inhomoginities, particularly phase domains in ultra thin layer, without the use of special probes. The reflected light is the basis of the Brewster Angle Microscopy of the ultra‐thin films. Imaging of these monolayers yield to many morphological/phase transition based study of these monolayers. The development set up consist of p‐polarized light, designed optics, frame grabber card, CCD camera as detector and teflon trough with barrier mechanism. Movement of a teflon barrier is controlled with stepper motor. An intelligent module based on single chip microcontroller 89C51 is developed for controlled barrier movement. With BAM, the real time image of a monolayer can be viewed on PC monitor. Stored images can be analyzed further through software package developed under VC++. In house software development has been completed at NCL, for instrument control, image acquisition, and image analysis. Standard APIs available with frame grabber cards can not be made applicable for this real time application. A special algorithm has been developed for finding out the area of the interested domain marked by the user. Other analysis software function includes file management, magnification of the image, contrast and brightness control, etc. A standard monolayer of Stearic acid is used for testing purpose. The instrumentation performance has been tested with an amount of 50 microliter of concentration 1 mg/ml Stearic acid spread on the subphase and found satisfactory. Sub phase used was high purity water (Millipore Milli‐ Q) contained in Teflon trough. The monolayer is compressed using teflon barrier. Simultaneously real time imaging was done to record the first order phase behavior of the monolayer. The instrument testing was done with the help of Nanoscience group at NCL. Recently instrument automation has been updated using LabVIEW platform. With LabVIEW addition, simultaneous viewing of compressed monolayer image and barrier movement control is possible beside other functions.