surface tension

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48 Terms

1
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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

2
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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

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surface active agents

-surfactants
-amphipathic compound
-colloidal substance

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surface active agents

substance whose molecules or ions move on their accord to the interface when dispersed in a liquid thereby reducing surface tension

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nonionic surfactants

spans and tweens

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anionic surfactants

"ate"
-sodium lauryl sulfate
-sodium dodesyl sulfate

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cationic surfactants

-"onium"/ "inium"
-benzalkonium chloride
-quats

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amphoteric surfactants

lecithin

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Griffin Hydrophilic-Lipophilic Balance System

-applicable for nonionic surfactants only

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HLB <10 (1-9)

-lipophilic
-suitable for making w/o emulsions
-spans

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HLB >10 (11-20)

-hydrophilic
-suitable for making o/w emulsions
-tweens

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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

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cohesive force

force of attraction between molecules of same phases

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adhesive force

force of attraction between molecules of different phases

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surface tension

the property of a liquid that allows it to resist an external force due to cohesive nature of the water molecules

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surface tension

the tendency of liquid surface to shrink into minimal surface area possible

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Hydrophile-lipophile balance (HLB)

-system of hydrophile-lipophile classification
-used to classify nonionic surfactants

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HLB less than 9- lipophilic surfactants

-forms w/o emulsions

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HLB >6

oil soluble

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HLB 1-3

antifoaming

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lipophilic surfactants example

-spans
-sorbitan
-esters

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HLB more than 9 - hydrophilic surfactants

forms w/o emulsions

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hydrophilic surfactants example

tweens, polyoxyethylene derivatives of spans

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1-3

antifoaming agents

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4-6

w/o emulsifying agt

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7-9

wetting and spreading agt

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8-18

o/w emulsifying agt

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13-15

detergents

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16-18

solubilizing agts

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w/o

cholesterol and its derivatives

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o/w

high mw monohydrate alcohols (cetyl, stearyl, glycerin)

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wilhelmy plate method or ring method

quick and easy to operate

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du nuoy method or tensiometric method

satisfactory

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sessile drop method

vg

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capillary rise method

vg

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buddle pressure method

vg

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drop wt method

suitable

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drop wt method

most common method used for the surface tension determination

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drop wt method
at equilibrium,

the upward force is equal to the downward force

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drop wt method equipment

stalagmometer

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drop wt method

several drops of liquid leaked out ot the stalagmometer are weighed

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high no of drops

= low density and surface tension= high surface area

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emulsifiers

a surfactant which adsorbs at the newly formed oil-water interface during emulsion preparation

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emulsifiers

protects the newly formed droplets against immediate recoalescence

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pharmaceutical uses of emulsifiers

major constituents of pharmaceutical, cosmetics, and food semisolid preparation many of which are emulsifiers

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topical dosage forms

spreading coefficient- lotions, creams, sunscreen and cosmetics

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solid dosage forms

-wetting agents to enhance drug dissolution rate
-lubricants, anti-adherents, glidants to reduce friction

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liquid dosage forms

solubilizing agents to enhance drug dissolution