Chemistry Reference
In-Depth Information
Head group (surfactant).
A term referring to the portion of a surfactant molecule
that imparts solubility to the molecule. Generally used in the context of water
solubility.
Hydrogen bonding.
Interaction between molecules or portions of a molecule
resulting from the Lewis acid or base properties of the molecular units. Most
commonly applied to water or hydroxyl containing systems (e.g., alcohols) in
the sense of Brønsted-Lowry acid-base theory, but also found in molecules hav-
ing hydrogen bound to nitrogen (amines and amides).
Hydrophile-lipophile balance (HLB).
An essentially empirical method for quan-
tifying or estimating the potential surface activity of a surfactant based on its
molecular constitution—used primarily in emulsion technology.
Hydrophilic (''water-loving'').
A descriptive term indicating a tendency on the
part of a species to interact strongly with water, sometimes equated with ''lipo-
phobic,'' defined below.
Hydrophobic (''water-hating'').
The opposite of hydrophilic, having little ener-
getically favorable interaction with water—generally indicating the same char-
acteristics as lipophilic, except that some hydrophobic materials (e.g., perfluoro
organics) can also be lipophobic.
Interface.
The boundary between two immiscible phases. The phases may be
solids, liquids, or vapors, although there cannot, in principle, be an interface
between two vapor phases. Mathematically, the interface may be described as
an infinitely thin line or plane separating the bulk phases at which there will
be a sharp transition in properties from those of one phase to those of the
other, although in fact it will consist of a region of at least one molecular thick-
ness, but often extending over longer distances.
Interfacial tension.
The property of a liquid-liquid interface exhibiting the char-
acteristics of a thin elastic membrane acting along the interface in such a way as
to reduce the total interfacial area by an apparent contraction process—thermo-
dynamically, the interfacial excess free energy resulting from an imbalance of
forces acting on molecules of each phase at or near the interface (see
Surface
tension
).
Lipophilic (''fat-loving'').
A general term used to describe materials that have a
high affinity for fatty or organic solvents; essentially the opposite of hydrophilic.
Lipophobic (''fat-hating'').
The opposite of lipophilic; that is, materials prefer-
ring to be in more polar or aqueous media; the major exceptions are the fluoro-
carbon materials, which may be both lipophobic and hydrophobic.
London forces.
Forces arising from the mutual perturbation of the electron clouds
of neighboring atoms or molecules; generally weak (
8 kJ/mol), decreasing approx-
imately as the inverse sixth power of the distance between the interacting units.
Lyophilic (''solvent loving'').
A general term applied to a specific solute-solvent
system, indicating the solubility relationship between the two. A highly water-
soluble material such as acetone would be termed lyophilic in an aqueous
context.
