EXP 8 (POST LAB) Flashcards
When phases exist together, the boundary between two of them is termed an
interface
The properties of the molecules forming the interface are often sufficiently different from those in the bulk of each phase that they are referred to as forming an
interfacial phase
Several types of interface can exist, depending on whether the two adjacent phases are in the solid, liquid or gaseous state.
Interfacial Phenomena
is a property of liquids that results from the tendency of liquids to minimize their surface area
Surface Tension
The property of the surface of a liquid that allows it to resist an external force, due to the cohesive nature of its molecules
Surface Tension
This “tension” of surface, is the
force per unit length
This force, the surface tension, has the units
dyne/cm in the cgs system.
Surface Tension
– caused by _____ of surface molecules
cohesion
Application of Interfacial Phenomena in Pharmacy
� To control the droplet size of pharmaceutical drops (e.g. ophthalmic solutions)
� Emulsion formation and stability
� Dispersion of insoluble particles in liquid media to form suspensions
� Dissolution of drugs
� Spreadability of topical preparations
Factors affecting surface tension:
� Temperature
� Presence of impurities
� Intermolecular force
� Density
� Viscosity
� Addition of surfactants
Is the force per unit length existing at the interface between two immiscible liquid phases
Interfacial tension
Interfacial tension
� Is the force per unit length existing at the interface between two immiscible liquid phases and like surface tension, has the units of
dyne/cm
are the molecules and ions that are adsorbed at interfaces.
Surface-active agents or surfactants
Surface-active agents or surfactants are the molecules and ions that are ____ at interfaces.
adsorbed
Surface-Active Agents
This is also known as ______, which the molecule or ion has the affinity for both polar and nonpolar solvents.
Amphiphile
In an amphipilic structure there are groups with opposite properties, one with the affinity to ____ and one with the affinity to___
water; lipids
Anionic surfactants:
❑ carries a negative charge such as R-COO−, RSO4−, or RSO3−
❑ most widely and extensively in detergents, shampoos, and body cleansers
❑ e.g. sodium dodecyl sulfate, sodium stearate, alkylpolyoxyethylene sulfate, triethanolamine oleate
carries a negative charge such as R-COO−, RSO4−, or RSO3−
Anionic surfactants:
most widely and extensively in detergents, shampoos, and body cleansers
Anionic surfactants:
e.g. sodium dodecyl sulfate, sodium stearate, alkylpolyoxyethylene sulfate, triethanolamine oleate
Anionic surfactants:
Cationic surfactants:
❑ have a cationic group, a functional group that can be positively charged at certain pH values.
❑ most are quaternary ammonium compounds
❑ used in fabric softeners and hair conditioners
❑ have antibacterial activity
❑ e.g. benzalkonium chloride, cetrimide, cetylpyridinium chloride
❑ have a cationic group, a functional group that can be positively charged at certain pH values.
Cationic surfactants:
❑ most are quaternary ammonium compounds
Cationic surfactants:
❑ used in fabric softeners and hair conditioners
Cationic surfactants:
❑ have antibacterial activity
Cationic surfactants:
e.g. benzalkonium chloride, cetrimide, cetylpyridinium chloride
Cationic surfactants:
Non-ionic surfactants:
❑ contain ether and/or hydroxyl [–OH] hydrophilic groups
❑ commonly used for stabilizing oil-in-water (o/w) and water-in-oil (w/o) emulsions.
❑ e.g. Spans
Tweens
❑ contain ether and/or hydroxyl [–OH] hydrophilic groups
Non-ionic surfactants:
❑ commonly used for stabilizing oil-in-water (o/w) and water-in-oil (w/o) emulsions.
Non-ionic surfactants:
❑ e.g. Spans
Tweens
Non-ionic surfactants:
Amphoteric/Ampholytic surfactants:
❑ possess both cationic and anionic groups in the same molecule
❑ Decreases irritancy in formulations
❑ Lecithin - an ampholytic surfactant and is used for parenteral emulsions
❑ Examples: alkylbetaine, alkylamidopropylamine N oxide
possess both cationic and anionic groups in the same molecule
Amphoteric/Ampholytic surfactants:
Decreases irritancy in formulations
Amphoteric/Ampholytic surfactants:
an ampholytic surfactant and is used for parenteral emulsions
Lecithin
Examples: alkylbetaine, alkylamidopropylamine N oxide
Amphoteric/Ampholytic surfactants:
is the balance of the size and strength of the hydrophilic and lipophilic moieties of a surfactant molecule
Hydrophilic-Lipophilic Balance (HLB) System
HLB Value Range Surfactant Application
Antifoaming agents
0-3
HLB Value Range Surfactant Application
W/O emulsifying agents
4-6
HLB Value Range Surfactant Application
Wetting agents
7-9
HLB Value Range Surfactant Application
O/W emulsifying agents
8-18
HLB Value Range Surfactant Application
Detergents
13-15
HLB Value Range Surfactant Application
Solubilizing agents
10-18
defined as the time (in seconds, s) necessary for a given amount of powder to penetrate the still surface of water.
Wettability
Wettability IS INCREASED BY?
SURFACTANTS
Wettability Affects the
rate of dissolution
A wetting agent, is a surfactant that, when dissolved in water, lowers the advancing ______ and aids in displacing an air phase at the surface and replacing it with a ____ phase.
contact angle; liquid
Wetting Agent
EXAMPLES:
Propylene glycol, Glycerin, Mineral Oil
The contact angle between a liquid and a solid may by 0°, signifying _____, or it may approach 180°, at which wetting is ____.
complete wetting; insignificant
CONTACT ANGLE: 180 DEG.
NON-WETTING
CONTACT ANGLE: >90 DEG.
HIGH WETTING
CONTACT ANGLE: <90 DEG.
LOW WETTING
CONTACT ANGLE: 0 DEG.
PERFECT WETTING
Application of Wetting Agents
❖ Used to increase the
rate of dissolution
Application of Wetting Agents Used in the preparation of
suspensions
Methods For Measuring Specific Gravity
- Du Nouy
- Wilhelmy plate
3.Pendant Drop
4.Sessile Drop method
5.Capillary rise method
- Du Nouy- measures the ________ by the surface
maximum pull on the ring
- Wilhelmy plate - measures ______
equilibrium surface or interfacial tension
3.Pendant Drop – based on the ____of the drop.
shape
4.Sessile Drop method– based on the ____ of the drops
size
5.Capillary rise method – measures the ____ of the liquid in side the _____
rise; capillary tube
The traditional method used to measure surface or interfacial tension.
Du Noüy Ring method:
Du Noüy Ring method:
______ of the surface or interface have little influence on this measuring technique.
Wetting properties
Maximum pull exerted on the ring by the surface is measured.
Du Noüy Ring method
Du Noüy-Padday method:
A minimized version of Du Noüy method uses a ______ instead of a ring, in
combination with a _______ to record maximum pull.
small diameter metal needle
high sensitivity microbalance
is a thin plate that is used to measure
equilibrium surface or interfacial tension at an air-liquid or liquid liquid interface.
Wilhelmy plate
A Wilhelmy plate is a thin plate that is used to measure
equilibrium surface or interfacial tension at an _______.
air-liquid or liquid liquid interface
Wilhelmy plate
In this method, the plate is oriented ______ to the interface, and the _____ exerted on it is measured.
perpendicular; force
The liquid is injected from a needle so that it forms a drop on the tip of the needle.
Pendant drop method
Pendant drop method
The drop is then optically observed and the ______ is calculated from the ____ of the drop.
surface tension; shape
� Surface tension is derived from the contact angle.
Sessile Drop Method
Capillary –action occurs when the _____ to the walls is stronger than the _____ forces between the liquid molecules.
adhesion; cohesive
The _____ to which capillary action will take water in a uniform circular tube is limited by _____
height; surface tension
Experiment No. 8 Theoretical Results.
� Capillary method:
Ethanol:
Water:
Mineral Oil:
0.787 g/mL
1 g/mL
0835 g/mL
Surface tension is directly proportional to the _____ of the liquid.
density
The higher the density, the _____the surface tension.
higher
Experiment No. 8 Theoretical Results.
� Effect of surfactans:
Effect on number of drops =
increases the number of drops by lowering surface tension of liquids.
Effect of surfactans:
Effect on wettability of powders =
increases wettability of powders.
