Surface tension and surfactants

If 2 liquids are completely miscible with each other, the interfacial tension is what

0; no interfacial tension exists between them

Applications of surfactants:

1. Emulsifying agents 2. Detergents 3. Wetting agents 4. Solubilizing agents 5. Antibacterial 6. Aids to the adsorption of drugs in the body

Depending on the number and nature of the polar and non polar groups, amphiphiles may act as:

1. Hydrophilic 2. Lipophilic or 3. Reasonably well-balanced

Detergency removes foreign matter from surfaces by this process:

1. Initial wetting of the dirt and surface 2. Deflocculation and suspension 3. Emulsification or solubilization of dirt particle 4. Foaming for entrainment and washing away of particles

Negative adsorption is also called

ABsorption

What can be used as antifoaming agents?

Alcohol, ether, castor oil, and some surfactants

Classification of amphiphiles (surfactants):

Anionic Cationic Nonionic Ampholytic

The concentration of monomer (surfactants) at which micelles form is called

Critical micelle concentration (CMC)

Solubilizing agents have ______ HLB

High (hydrophilic)

_________ increases the cohesion in liquids

Hydrogen bonding

Tweens (polyoxyethylene derivatives of the spans) are _______ and have ______ HLB

Hydrophilic High (9.6-16.7)

What is the HLB scale

Hydrophilic-Lipophilic balance

Which is less- interfacial tension or surface tension

Interfacial tension

What are 2 forces that can act on liquids?

Intermolecular forces (van der Waals) and hydrogen bonding

Spans (sorbitan esters) are ______ and have _____ HLB

Lipophilic Low (1.8-8.6)

Antifoaming agents have ______ HLB

Low (lipophilic)

Positive adsorption

Phenomenon where the added molecules concentrate more on the *surface of the adsorbent* (at the interface) than in the bulk

A foam is:

a relatively stable structure consisting of air pockets enclosed within thin films, the gas-in-liquid diversion being stabilized by a foaming agent

Surfactant defintion

a substance that tends to reduce the surface tension of the liquid in which it is dissolved

Surfactants are molecules that are

absorbed at the interfaces

Any further addition of amphiphiles (surfactant) in excess of the critical micelle concentration will

aggregate to form micelles

As the concentration of amphiphiles (surfactants) increases, _______ occurs over a narrow concentration range

aggregation (formation of micelles)

Surfactants are also known as _______

amphiphiles (has affinity for both polar and non polar solvents)

Dimethyldodecylammonium-propane sulfonate is

ampholytic

Sodium lauryl sulfate is

anionic

Molecules _______ can only develop attractive cohesive forces with other liquid molecules that are below or adjacent to them

at the surface

Cetyl trimethylammonium bromide is

cationic

Surface tension ______ up to the CMC

decreases

The foams ______ as the liquid drains away from the area surrounding the air globules

dissipates

Surfactants are used a lot in:

emulsions (think emulsifying agents)

What doe the HLB scale do

helps to establish an HLB range of optimum efficiency for each class of surfactant

Any expansion of the surface ______ the free energy of the system

increases

Force per unit length at the interface between 2 *immiscible* liquids (o/w) is

interfacial tension

A wetting agent is a surfactant that:

is dissolved in water and then lowers the advancing contact angle and aids in displacing an air phase at the surface and replacing it with a liquid phase

These aggregates (which may contain 50 or more monomers) are called:

micelles

Liquid interfaces are

molecules in the bulk of the liquid that are surrounded in all directions by other molecules for which they have equal attraction

Polyoxyethylene lauryl ether is

nonionic

After the CMC is reached, surface tension

remains constant

Surfactants work in detergents because they are used to:

remove dirt

Amphiphiles (surfactants) when present in *low* concentration, exist _______

separately

A ______ has the smallest surface area per unit volume

sphere

The force per unit length that must be applied parallel to the surface as to counterbalance the net inward pull is

surface tension (dyne/cm)

Negative adsorption

the added materials are concentrated in the *bulk* instead of the adsorbent

At the oil-water interface, the lipophilic chains of surfactants are associated with _______

the oil phase

Surface free energy is defined by

the work required to increase the surface area A of the liquid by 1 area unit

So basically all that said is:

there is a certain concentration (CMC) of surfactant that is added to a solvent that will decrease the surface tension bc it forms these micelles

The most important property of the wetting agent is:

to lower the contact angle between a liquid droplet and surface over where it spreads

Such forces pulls the molecules of the interface ______ and _______ the surface; this is called:

together; contracts Surface tension

At the air-water interface, the lipophilic chains of surfactants are directed ________

upwards into the air

Both of these are _______ than covalent or ionic forces

weaker