BAM - Brewster Angle - Langmuir-Blodgett




Brewster Angle Microscopes enable observation of monolayers, typically at the air-water interface using a Langmuir Trough.
KSV NIMA is now happy to announce that this is possible also on standard vessels thanks to our new Stand-Alone MicroBAM.
They create an image of the surface by detecting changes in the refractive index of the water surface in the presence of surfactant molecules.
It provides information on homogeneity, phase behaviour and film morphology.


A Brewster Angle Microscope (BAM ) enables the visualization of Langmuir monolayers or adsorbate films at the air-water interface.
In conjunction with a Langmuir Trough, it enables the study of:

- Monolayer/film behaviour
- It is possible to observe phase changes, phase separation, domain size, shape and packing.
- Monolayer/film homogeneity
- When combined with a KSV NIMA L & LB Trough, observation can be performed during compression/expansion at known surface pressures.
- Influence of subphase conditions on film structures
- Observe and study monolayer/film behaviour and formation in different subphase conditions including salt concentrations, pH and temperature to name a few (e.g. Gibbs adsorption layers).
- Monitoring of surface reactions
- For example, photochemical reactions, polymerisation reactions as well as enzyme kinetics can be followed in real time.
- Monitoring and detection of surface active materials
- For example protein adsorption and nanoparticle flotation.
- BAMs are primarily designed for the air-water interface. However under some conditions the KSV NIMA BAM can be used for other interfaces such as air-glass.

Working principle

Brewster Angle Microscopes utilize the fact that when p-polarized light is guided towards an air-water interface, no reflection occurs at a certain incident angle. This angle, the Brewster angle, is determined by Snell´s law and depends on the refractive indices of the materials in the system.

Snell's law: tan "alpha" = n2 / n1

where "alpha" is the Brewster angle in radians, n1 the refractive index of air (about 1) and n2 the refractive index of water (about 1.33).
The Brewster angle for the air-water interface is approximately 53°, and under this condition the image of a pure water surface appears black as no light is reflected. Addition of material to the air-water interface modifies the local refractive index (RI), and hence, a small amount of light is reflected and displayed within the image. The displayed image contains areas of varying brightness determined by the particular molecules and packing densities across the sampling area.

KSV NIMA offers two different Brewster Angle Microscopes, the advanced KSV NIMA BAM and the compacts KSV NIMA MICROBAM and STAND-ALONE MICROBAM, which allows the monolayer imaging characterization in real-time also on vessels.