surface tension

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