1. Kwame Nkrumah University of
Science & Technology, Kumasi, Ghana
Pharm 231
States of Matter: Liquids, solids and
gases
Frederick W. A. Owusu, PhD
Department of Pharmaceutics
FPPS, CHS,KNUST
frederickakuffo.owusu@knust.edu.gh
7. BINDING FORCES BETWEEN MOLECULES
• Intermolecular forces are attractive forces
between molecules
• Intramolecular forces hold atoms together
• Generally, intermolecular forces are much
weaker than intramolecular forces
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8. INTERMOLECULAR FORCES
• Cohesion is the intermolecular attraction
between like molecules
• Adhesion is an attraction between unlike
molecules
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9. Applications of Intermolecular Forces
Understanding of:
• properties of gases, liquids and solids
• interfacial phenomena
• Flocculation in suspensions
• Stabilization of emulsions
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• What intermolecular forces exist in the
following compounds?
• Helium, Nitrogen, Propane, Methyl Chloride,
Isobutane, Butane, Ethyl ether, Carbon disulfide,
Ethyl Alcohol, Water
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Liquid Crystals
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The term liquid crystal is an apparent
contradiction, but it is useful in a
descriptive sense since materials in this
state are in many ways intermediate
between the liquid and solid states.
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Structure of Liquid Crystals
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• Molecules in the liquid state are mobile
in three directions and can also rotate
about three axes perpendicular to one
another
• In the solid state, on the other hand,
they are immobile, and rotations are not
possible
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Liquid Crystalline State
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• It is not unreasonable to suppose, therefore,
that intermediate states of mobility and
rotation should exist, as in fact they do
• It is these intermediate states that constitute
the liquid crystalline phase, or mesophase, as
the liquid crystalline phase is called
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Liquid Crystals
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• The two main types of liquid crystals are termed
smectic (soap- or grease-like) and nematic (thread-
like)
• In the smectic state, molecules are mobile in two
directions and can rotate about one axis
• In the nematic state, the molecules again rotate only
about one axis but are mobile in three dimensions
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Liquid Crystals
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• A third type (cholesteric crystals) exist but may be
considered as a special case of the nematic type.
• The smectic mesophase is probably of most
pharmaceutical significance since it is this phase
that usually forms in ternary (or more complex)
mixtures containing a surfactant, water, and a
weakly amphiphilic or nonpolar additive
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Liquid Crystals
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• In general, molecules that form mesophase are organic,
are elongated and rectilinear in shape, rigid, and
possess strong dipoles and easily polarizable groups
• The liquid crystalline state may result either from the
heating of solids (thermotropic liquid crystals) or from
the action of certain solvents on solids (lyotropic
liquid crystals).
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Liquid Crystals
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• The first recorded observation of a
thermotropic liquid crystal was made by
Reinitzer in 1888 when he heated cholesteryl
benzoate.
• At 1450 C, the solid formed a turbid liquid
(the thermotropic liquid crystal), which only
became clear, to give the conventional liquid
state, at 1790 C.
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Properties and Significance of Liquid
Crystals
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• Due of their intermediate nature, liquid crystals
have some of the properties of liquids and some of
solids.
• For example, liquid crystals are mobile and thus
can be considered to have the flow properties of
liquids.
• At the same time they possess the property of
being birefringent, a property associated with
crystals.
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Properties and Significance of Liquid
Crystals
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• In birefringence, the light passing through a
material is divided into two components with
different velocities and hence different
refractive indices.
• Some liquid crystals show consistent colour
changes with temperature, and this
characteristic has resulted in their being used
to detect areas of elevated temperature under
the skin that may be due to a disease process.
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Properties and Significance of Liquid
Crystals
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• Nematic liquid crystals are sensitive to
electric fields, a property used to advantage
in developing display systems.
• The smectic mesophase has application in
the solubilization of water-insoluble
materials
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Properties and Significance of Liquid
Crystals
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• It also appears that liquid crystalline phases of
this type are frequently present in emulsions
and may be responsible for enhanced physical
stability owing to their highly viscous nature.
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Properties and Significance of Liquid
Crystals
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• The liquid crystalline state is widespread in nature,
with lipoidal forms found in nerves, brain tissue,
and blood vessels
• Atherosclerosis may be related to the laying down
of lipid in the liquid crystalline state on the walls of
blood vessels.
• The three components of bile (cholesterol, a bile
acid salt, and water), in the correct proportions, can
form a smectic mesophase and this may be
involved in the formation of gallstones.
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Properties and Significance of Liquid
Crystals
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• Bogardus applied the principle of liquid
crystal formation to the solubilization and
dissolution of cholesterol, the major
constituent of gallstones
• Cholesterol is converted to a liquid crystalline
phase in the presence of sodium oleate and
water, and the cholesterol rapidly dissolves
from the surface of the gallstones.
