Coarse dispersions are heterogeneous systems where the dispersed particles are larger than 1000 nm. They are characterized by relatively fast sedimentation. The dispersed phase may be easily separated from the continuous phase by filtration. A pharmaceutical suspension is a coarse dispersion where the internal phase is uniformly dispersed throughout the external phase. The internal phase typically has particle sizes between 0.5-5 microns. Suspensions demonstrate properties like pseudoplasticity and thixotropy which influence stability during manufacture and storage.

1. Coarse
Dispersion

2. What mean by coarse?
 Coarse dispersions are heterogeneous
dispersed systems, in which the dispersed
phase particles are larger than 1000 nm.
Coarse dispersions are characterized by
relatively fast sedimentation of the dispersed
phase caused by gravity or other forces.
Dispersed phase of coarse dispersions may
be easily separated from the continuous
phase by filtration.

3. Dispersed
system
• The term "Disperse S ys t e m " refers
to a system in which one substance
(The Dispersed Phase) is
distributed throughout a second
substance (the continuous P h a s e ).
• Suspensions are heterogenous
system consisting of 2 phases.

4. Suspension
 A Pharmaceutical suspension is a coarse dispersion in
which internal phase (therapeutically active
ingredient)is dispersed uniformly throughout the external
phase.
 The internal p h a s e consisting of insoluble solid
particles having a range of size 0.5 t o 5 mic ro n s
which is maintained uniformly through out the
suspending vehicle with aid of s i n g l e o r
c o m b i n a t i o n o f s u s p e n d i n g a g e n t .
 The external phase ( s u s p e n d i n g m e d i u m ) is
generally aqueous in some instance, m a y be an
organic or oily liquid for non oraluse.

8. DLVO Theory
 DLVO stands for Derjaguin, Landau, Verway and
Overbeek.
 According to this theory the distance between two
dispersed particles mainly influence the particle -
particle interaction.

9. DLVO Theory
 Consider two colloidal particles.
 There will exist two types of interaction in these particles as force of
attraction and force of repulsion.
 When repulsion predominates the particles will not aggregate.
 But when attractive forces are more the particles will form aggregate.
 DLVO theory mainly gives relationship between potential energy
versus interparticulate distance.

10. DLVO Theory
Net Energy Peak

11. DLVO Theory
The interaction between particles is described below
 1) Forces of attraction: If potential energy between the
particles is low then there exists a attractive forces in
between particles. These forces are mainly Vander Wall
type forces.
 2) Forces of repulsion: If there exists any potential
energy in between the particles then particles will repel
each other. This potential energy is present due to
charges present on colloidal particles and electrical
double layer.

12.  Net Energy of Interaction: If we combine these two forces i.e. attractive and
repulsive forces then we get net energy of interaction denoted by dotted line.
 Primary Minimum (sign of precipitation): When we bring particles very
close to each other, there orbitals overlap and penetrate with each other due to
which there is presence of strong attractive force and particles will form
precipitation.
 Secondary minimum (sign of precipitation): This is observed when particles
are separated by long distance and there is presence of electrolytes. These
electrolyte will settle in between the particles and form floccules due to which
particles will be attracted to each other though distance in between them is
more. At this point potential energy will be minimum because particles are far
from each other.

13. DLVO Theory
 Net Energy peak (Sign of Better stability): At intermediate
distance a good amount of repulsive forces exists because of zeta
potential present on colloidal particles. This potential barrier keeps
the particles in Brownian motion and gives stability to dispersion.
At this point there exists a maximum potential energy in between
colloidal particles.

26. DEFINITION
 An emulsion is a thermodynamically unstable system consisting of at least
two immiscible liquid phases, one of which is dispersed as globules (the
dispersed phase) in the other liquid phase (the continuous phase), stabilized
by the presence of an emulsifying agent.
 The particle diameter of the dispersed phase generally extends from about
0.1 to 10 μm, although particle diameters as small as 0.01 μm and as large
as 100 μm.

39. Microemulsion

53. Theories of Emulsions
 Monomolecular Adsorption theory
 Oriented-Wedge Theory
 Oriented adsorption theory
 Plastic or Interfacial film theory
 Surface tension theory
 Interfacial tension theory
 Fischer’s theory of hydrates and solvates
 Viscosity theory

54. Monomolecular
Adsorption theory
Concept
Surface-active agents, or
oil- water
amphiphiles, reduce interfacial tension
interface to form
because of their adsorption at the
monomolecular films.

55. Explanation
 In practice, combinations of emulsifiers rather than single agents are
used most frequently today in the preparations of emulsions.
Hydrophilic emulsifier in the aqueous phase and a hydrophobic agent
in the oil phase to form a complex film at the interface.
Example
 Three mixtures of emulsifying agents at the oil–water
interface. The combination of Sodium cetyl sulfate
and cholesterol leads to a complex film that produces
an excellent emulsion.
 Sodium cetyl sulfate and 0leyl alcohol do not form a
closely packed or condensed film, consequently,
their combination results in a poor emulsion.

56. Oriented-Wedge
Theory
Concept
 This theory deals with formation of monomolecular layers of emulsifying agent curved
around a droplet of the internal phase of the emulsion.
A. Emulsifier molecules oriented at interface. Dotted lines indicate the large volume occupied
by polar head due to formation of hydrated complex.
B. Shows that close packing of molecules ‘ fits’ this curvature.
Example
 In a system containing two immicible liquids, emulsifying agents would be preferentially
soluble in one of the phases and would be embaded in that phase.

57. As per this theory, the added emulsifying agent forms a mechanical
film by getting adsorption at the interface of the liquid and offers
stability to emulsion.
 However,this theory could not explain the formation of type of
emulsion.
Oriented adsorbtion
theory

58. Interfacial film theory
 Interfacial film theory places the emulsifying agent at the
interface between the oil and water, surrounding the droplets of the internal
phase as a thin layer of film adsorbed on the surface of the drops.
 The formation of an o/w or a w/o emulsion depends on the degree of
solubility of the agent in the two phases, with water-soluble agents
encouraging o/w emulsions and oil-soluble emulsifier the reverse.

59. Surface tension
theory
 According to the surface tension theory of emulsification, the emulsifying agents cause a
reduction in the interfacial tension of the two immiscible liquids, reducing the repellent
force between the liquids and withdrawing the attraction of liquids for their own
molecules. In this way, the surfactants convert large globules into small ones and avoid
small globules from coalescing into large ones.
 In this way, the surfactants convert large globules into small ones and avoid small globules
from coalescing into large ones.

60. Interfacial tension
theory
 When two immiscibleliquids come in contact, the force causing each
liquid to resist breakage is known as interfacial tension.
When a high interfacial tension existed between two liquids
emulsification is difficult, and if the tension could be reduced
emulsification facilitated.
 The explanation that in oil in water dispersion, the interfacial
tension is so great that when two globules of dispersed phase
approach each other it withdraws the
liquid from between them, with the result they coalesce. When the
interfacial tension is greatly reduced by the addition of
emulsifier the globules remain separate.

61.  Fischer’s observed that the use of specific ratios of
emulsifying agent to
 continuous phase, he claimed that the quantity of water
in these specified
 ratios was all used up in forming a colloidal hydrate.
Fischer’s theory of
hydrates and solvates
 This theory does not attempt to explain the formation of
concentrated emulsions and not explains how globules in an
emulsion are prevented from coalescing and separation into two
layers.

62. Viscosity theory
As per this theory, an increase in viscosity of an emulsion will lead
to an increase in the
stability.
This theory failed to explain about the milk which shows
considerable stability even though its viscosity is less.
This theory is holds good for emulsions prepared with gums as
emulsifying agents, but it collapse or no explanation of emulsions
made which comparatively low viscosity and great stability

63. Preservation of emulsion
 Microbial contamination may occur due to:
 contamination during development or
production of emulsion or during its use.
 Usage of impure raw materials
 Poor sanitation conditions
 Invasion by an opportunistic microorganisms.
 Contamination by the consumer during use of
the product.
Precautions to prevent microbial growth ;
 Use of uncontaminated raw materials
 Careful cleaning of equipment with steam .

64. The preservative must be :
 Less toxic .
 Stable to heat and storage
 Chemically compatible
 Reasonable cost
 Acceptable taste, odor and color.
 Effective against fungus, yeast, bacteria.
 Available in oil and aqueous phase at
effective level concentration.
 Preservative should be in unionized state to
penetrate the bacteria.
 Preservative must no bind to other
components of the emulsion

65. Examples of antimicrobial preservatives
used to preserve emulsified systems
include
 parahydroxybenzoate esters such as
methyl, propyl and butyl parabens,
 organic acids such as ascorbic acid and
benzoic acid,
 organic mercurials such as
phenylmercuric acetate and
phenylmercuric nitrate,
 quaternary ammonium compounds such
as cetrimide,
 cresol derivatives such as chlorocresol
 and miscellaneous agents such as
sodium benzoate, chloroform and
phenoxyethano

66. Antioxidant must be….
 Nontoxic, nonirritant,
 effective at low concentration under
the expected conditions of storage
and use,
 soluble in the medium and stable.
 Antioxidants for use in oral preparation
should also be odorless and tasteless.

67. Examples of antioxidants
 Gallic acid, Propyl gallate
 Ascorbic acid – Suitable for oral use products
 Sulphites - Suitable for oral use products
 L-tocopherol - pharmaceuticals and
cosmetics - Suitable for oral preparations e.g.
those containing vit A
 Butylated hydroxyl toluene - pharmaceuticals
and cosmetics - Pronounced odor, to be used
at low conc.
 Butylated hydroxylanisol - pharmaceuticals
and cosmetics

68. Rheological Properties
suspension
 Suspensions & emulsions falls under the category of
coarse dispersion systems.
 In suspensions & emulsions, the flow properties have
major influence in the manufacture, during storage &
administration of drugs.
 The flow properties such as pseudo plastic & thixotropy
are important for physical stability of suspensions.
 For emulsions flow type may vary according to their
concentration.

69. RHEOLOGICAL PROPERTIES OF SUSPENSIONS
 During storage, the suspensions exhibit gel like
structure & lowers the rate of settling.
 On moderate shaking, the product assumes sol-like
behaviour, which permit pouring of the product from
the bottle.
 The sol like behaviour also helps in uniform spreading
of dermatological preparations.
 Therefore, in order to maintain these properties the
flow properties should be studied.
 Dispersion medium is largely responsible for
determining the rheology of the suspensions.
 The preformulation studies include evaluation of
vehicles used in the suspension. An optimum viscosity
of this medium should be selected through
experimentation.

70.  Rheological evaluation is used as a quality control
parameter for comparing products.
 The consistency of suspensions are evaluated
using cup & bob or cone & plate viscometers.
 These are not applicable for flocculated
suspensions because the structure of the flocs are
destroyed during the analysis.

71. RHEOLOGICAL PROPERTIES OF EMULSIONS
 The following flow related attributes are desirable
for the overall performance of an emulsion
 Removal of an emulsion from a bottle or tube
 Flow of an emulsion through a hypodermic needle
 Spreadability of an emulsion on the skin
 Stress induced flow changes during manufacture

72.  The rheology of emulsions has many similar features to that
of suspensions. However, they differ in three main aspects
 The liquid/liquid interface that contains surfactant or polymer
layers introduces a response to deformation & one has to
consider the interfacial rheology
 The dispersed phase viscosity relative to that of the medium
has an effect on the rheology of the emulsion
 The deformable nature of the dispersed phase droplets,
particularly for large droplets, has an effect on the emulsion
rheology

73.  In general, dilute emulsions exhibit “Newtonian
flow”.
 As the viscosity of the emulsion increases,
flocculation of globules will be reduced because
the mobility of globules is restricted, leads to
creaming.
 Concentrated emulsions exhibit “non-Newtonian
flow”. Multipoint viscometers are used for
viscosity analysis.