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methods in determining surface tension
-wilhelmy plate or ring method
-du nuoy method or tensiometric method
-sessile drop method
-capillary rise method
-bubble pressure method
-drop weight method
surface tension
the force which the surface of one side of a line, one cm in length, pulls or attracts the surface of the other side of a line
surface active agents
-surfactants
-amphipathic compound
-colloidal substance
surface active agents
substance whose molecules or ions move on their accord to the interface when dispersed in a liquid thereby reducing surface tension
nonionic surfactants
spans and tweens
anionic surfactants
"ate"
-sodium lauryl sulfate
-sodium dodesyl sulfate
cationic surfactants
-"onium"/ "inium"
-benzalkonium chloride
-quats
amphoteric surfactants
lecithin
Griffin Hydrophilic-Lipophilic Balance System
-applicable for nonionic surfactants only
HLB <10 (1-9)
-lipophilic
-suitable for making w/o emulsions
-spans
HLB >10 (11-20)
-hydrophilic
-suitable for making o/w emulsions
-tweens
Interfacial tension
study of interfacial phenomena concerned with the properties of molecules situated at or near the boundary between 2 immiscible phases called the interface of the interfacial region
cohesive force
force of attraction between molecules of same phases
adhesive force
force of attraction between molecules of different phases
surface tension
the property of a liquid that allows it to resist an external force due to cohesive nature of the water molecules
surface tension
the tendency of liquid surface to shrink into minimal surface area possible
Hydrophile-lipophile balance (HLB)
-system of hydrophile-lipophile classification
-used to classify nonionic surfactants
HLB less than 9- lipophilic surfactants
-forms w/o emulsions
HLB >6
oil soluble
HLB 1-3
antifoaming
lipophilic surfactants example
-spans
-sorbitan
-esters
HLB more than 9 - hydrophilic surfactants
forms w/o emulsions
hydrophilic surfactants example
tweens, polyoxyethylene derivatives of spans
1-3
antifoaming agents
4-6
w/o emulsifying agt
7-9
wetting and spreading agt
8-18
o/w emulsifying agt
13-15
detergents
16-18
solubilizing agts
w/o
cholesterol and its derivatives
o/w
high mw monohydrate alcohols (cetyl, stearyl, glycerin)
wilhelmy plate method or ring method
quick and easy to operate
du nuoy method or tensiometric method
satisfactory
sessile drop method
vg
capillary rise method
vg
buddle pressure method
vg
drop wt method
suitable
drop wt method
most common method used for the surface tension determination
drop wt method
at equilibrium,
the upward force is equal to the downward force
drop wt method equipment
stalagmometer
drop wt method
several drops of liquid leaked out ot the stalagmometer are weighed
high no of drops
= low density and surface tension= high surface area
emulsifiers
a surfactant which adsorbs at the newly formed oil-water interface during emulsion preparation
emulsifiers
protects the newly formed droplets against immediate recoalescence
pharmaceutical uses of emulsifiers
major constituents of pharmaceutical, cosmetics, and food semisolid preparation many of which are emulsifiers
topical dosage forms
spreading coefficient- lotions, creams, sunscreen and cosmetics
solid dosage forms
-wetting agents to enhance drug dissolution rate
-lubricants, anti-adherents, glidants to reduce friction
liquid dosage forms
solubilizing agents to enhance drug dissolution