Spread Lipid Films on Liquid Surfaces (Langmuir–Blodgett Films) - Surface and Colloid Chemistry: Principles and Applications - page 70

Teflon Barrier

Monolayer

Clean
Surface

FIGure 4.1 Monolayer film balance: barrier and surface pressure.

air-water or oil-water interface, with its alkyl group pointing away from the water
phase. The alkyl group is at a lower energy state when pointing toward air than
when surrounded by water molecules. The molecular properties and applications are
therefore essential for investigation. The system can be easily considered as a two-
dimensional analog to the classical three-dimensional systems (as indicated by the
gas theory). Later experiments showed that these monomolecular films were relevant
to many more complicated systems.
It is thus seen that the Π of a monolayer is the lowering of surface tension due to the
presence of monomolecular film. This arises from the orientation of the amphiphile mol-
ecules at the air-water or oil-water interface, where the polar group would be oriented
towards the water phase, while the nonpolar part (hydrocarbon) would be oriented away
from the aqueous phase. This orientation produces a system with minimum free energy.
Later it was observed that, if a clean smooth solid is dipped through a mono-
layer, in most cases a single layer of lipid will be deposited on the solid. This film
was called the Langmuir-Blodgett (LB) film (Figure 4.2). Further, if this process is
repeated, multilayers could be deposited. This LB film technique has found many
applications in the electronics industry. Further, the presence of only one layer of
lipid changes the surface properties (such as the contact angle wetting, friction, light
reflection, charge, adhesion, etc.) of the solid.

Plate

FIGure 4.2 LB film formation (see text for details).