Amphiphile  A molecule containing both a hydrophilic (water loving) and a hydrophobic (water hating) part. These molecules assemble at the air-water interface.

Barriers  The rigid compression barriers on a Langmuir Trough, often made from PTFE or Delrin. Motor controlled barriers compress monolayer material at the water surface to form a compacted monolayer.

Bilayer  A two-molecule thick film. Typically formed by depositing two monolayers during LB deposition. One monolayer deposits on the downstroke and another layer on the upstroke to form a bilayer.

Collapse  A phenomenon that occurs within a monolayer when held at a surface pressure above the equilibrium spreading pressure of the monolayer material. Ejection of material from the 2D plane occurs to relax the surface pressure of the film. This results in the formation of 3D structures such as folds.

Delrin  A material used for manufacturing the compression barriers on Langmuir and LB Deposition Troughs. The material is composed of a polymer, polyoxymethylene. The highly electronegative oxygen component creates dipoles at the surface of the material, making the material hydrophilic. This hydrophilicity has been shown to offer enhanced monolayer film stability compared to using PTFE compression barriers.

Dipole  A separation of opposite charges, often seen within molecules. The presence of the highly electronegative oxygen in a molecule for example, can cause permanent molecular dipoles. A higher electron density in the bonds near the oxygen atom leads to a net negative charge. In neighbouring regions of the molecule, a net positive charge is caused by the reduced presence of outer electrons around the nuclei of neighbouring atoms. Dipoles are attracted to one another and explains the affinity of the polar head groups of amphiphilic molecules to water, another strongly polar material.

Equilibrium spreading pressure  The surface pressure at which a monolayer can coexist in equilibrium with material in crystal form. Compressed monolayers are only metastable and will eventually relax back to the equilibrium spreading pressure.

Hydrophilic  Water loving. Hydrophilic material will dissolve in water.

Hydrophobic  Water hating. Hydrophobic material will be repelled by water.

Isotherm  The short name for a surface pressure-area isotherm. A plot of the surface pressure of a compressed Langmuir film versus the confinement area of the film.

Langmuir film  A monolayer, specifically, one held at the air-water interface.

Langmuir, Irving  A research chemist in the early 20th Century responsible for determining much about the molecular properties of monolayer films.

Langmuir Trough  A scientific instrument used to form monolayers by confining molecules at the air-water interface.

LB deposition/technique  Named after Langmuir and Blodgett. The technique of immersing and withdrawing a substrate vertically into the Langmuir film to deposit a bilayer film. Repeated LB depositions form multilayer films.

LS deposition/technique  Named after Langmuir and Schaefer. The technique of depositing a single monolayer by lowering a substrate horizontally to make contact with the Langmuir film then lifting away.

Metastable  In the context of Langmuir films, the apparently stable condition of a film when viewed in a short time frame. Compressed films are not in equilibrium, they are metastable and will relax, usually by collapse, to their equilibrium spreading pressure.

Monolayer  A single molecule thick film, often formed at the air-water interface as a Langmuir film.

PTFE  Also called Teflon. A material used for manufacturing Langmuir and LB Deposition Trough tops and compression barriers. It is formed from a polymer, polytetrafluoroethylene, and is very hydrophobic. The material is very resistant to most solvents and is easy to clean.

Spreading  The deposition of monolayer material onto the subphase from a solution, using a syringe located only a few millimetres above the water surface.

Subphase  The reservoir of liquid upon which Langmuir films are formed.

Substrate  A solid support for the deposition of Langmuir films. Glass microscope slides and silicon wafers are among the most common types of substrate.

Surface pressure  The change in surface tension from the value for a clean subphase to the value in the presence of additional molecular matter.

Surface tension  The energy required to create a unit area of interface. This is measured as the force exerted around the perimeter of any probe penetrating the surface of a liquid.

Wilhelmy plate  The probe around which the air-water interface exerts surface tension, allowing the downward force to be measured at the surface pressure sensor. This is usually a 1cm x 2cm chromatography paper piece but can also be made of roughened platinum.