Applications of brewster angle microscopy to adsorbed species at the air/water interface

Abstract

This thesis describes the design and construction of a Brewster Angle Microscope (BAM) to investigate monolayer films at the air/water interface. A Schiff base coordination polymer, Cu(ll) 5,5'-methylenebis(N-hexadecyl- sallcylideneamine (poly(CuMBSH)), was initially investigated using the BAM equipment. This material is being developed as the active material in vapour sensing devices produced by the Langmuir Blodgett (LB) method. Transfer of the monomer (MBSH) to the substrate was found to be poor but poly(CuMBSH) had a good deposition ratio (>0.95). The film was polymerised at the air/water interface by injecting a solution of Cu(ll) ions into the subphase. BAM was able to record the polymerisation of MBSH to poly(CuMBSH) in real time. Qualitative image analysis indicates a reordering of the material at the interface and a decrease in film thickness. The technique of BAM clearly displays the change in structure between the monomer film and the polymer film and that the poly(CuMBSH) film is homogenous at the micron level. Poly(para-phenylenevinylenes) PPV derivatives are presently being examined as potential LED devices. One method used to produce such devices is the LB method. BAM was used to investigate ordering of the monolayer prior to deposition. Results by the Physics and Engineering department indicated that if subphase contained water that had been left to stand for several days film transfer was improved. A range of BAM experiments were conducted with varying subphases to determine the cause of this effect. A new technique of determining the surface excess concentration was developed in this work which is known as Brewster Reflectivity (BAR). The reflectivity of simple surfactants; sodium dodecylbenzenesulfonate, Getyltrimethylammonium bromide, tetradecyltrimethylammonium bromide and dodecyltrimethyl-ammonium bromide at concentrations above and below the critical micelle concentration (CMC) were correlated to surface excess. This is a new, simple, non-invasive method for probing the surface excess using intrinsic properties of the system.