Monolayer

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A monolayer is a single, closely packed layer of atoms or molecules [1]. A Langmuir monolayer is a one-molecule thick insoluble layer of an organic material spread onto an aqueous subphase. Traditional compounds used to prepare Langmuir monolayers are amphiphilic materials that possess a hydrophilic headgroup and a hydrophobic tail. Since the 1980s a large number of other materials have been employed to produce Langmuir monolayers, some of which are semi-amphiphilic, including macromolecules such as polymers. Langmuir monolayers are extensively studied for the fabrication of Langmuir-Blodgett film (LB films), which are formed by transferred monolayers on a solid substrate.

In biology monolayers are frequently encountered in for instance the phospholipid lipid bilayer structure of biological membranes.

The monolayer formation time or monolayer time is the length of time required, on average, for a surface to be covered by an adsorbate, such as oxygen sticking to fresh aluminum. If the adsorbate has a unity sticking coefficient, so that every molecule which reaches the surface sticks to it without re-evaporating, then the monolayer time is very roughly:

<math>t = 3 \times 10^{-4} / P</math>

where t is in seconds and P is the pressure in pascals. It takes about 1 second for a surface to be covered at a pressure of 300 µPa (2×10^-6 Torr).