Surfactants (Cut off for Exam 3)

Question 1

Surfactants

Answer 1

• Molecule or ion that can assist in adsorption at the interfacae
• AKA Surface active agent
• Are amphiphiles
• Can be predominately hydrophilic, hydrophobic, or balanced

Question 2

Formulation Approaches

Answer 2

• Surfactants reside at an energy minimum of dispersions
• Positive interaction with both layers causes interfacial tension or energy to be lowered
• O/W emulsions - choose surfactant that orients to water continuous phase
• W/O emulsions - choose surfantant that orients to oil continuous phase

Question 3

Hydrophilic/Lipophilic Classification

Answer 3

• Choose surfactant that orients the bulk of the surfactant into the continuous phase (maximizes the reduction of interfacial tension)
• HLB system - measure of surfactants preference for oil or water
• Low number: W/O emulsions
• High number: O/W emulsions

Question 4

HLB System

Answer 4

• Hydrophil-Lipophil Balance
• Categorizes emulsifying agents based on their chemical makeup
• Number assigned based on polarity
• Higher numbers for more polar/hydrophilic substances
• Can blend surfactants to produce optimal HLB

Question 5

HLB System Ranges

Answer 5

1-3: Antifoaming
3-6: W/O emulsifying agent
7-9: Wetting Agent
8-18: O/W emulsifying agent
13-15: Detergents
15-16: Solubilizers

Question 6

Film-Forming Polymers

Answer 6

• Hydrophilic colloidal polymers
• Weakly surface active
• Forms film between dispersed and continuous phases, producing stable emulsions
• EX: polyvinylpyrrolidone, hydroxyethylcellulose, starch, gums, proteins

Question 7

Solid Particulate Film-Formers

Answer 7

• Solid particles in the colloidal range
• Must be wetted by one of the liquids in the dispersion
• Collect at interface and form a stabilizing film
• Bentonite wetted by water for o/w emulsions
• Talc wetted by oil for w/o emulsions

Question 8

Wetting Agents

Answer 8

• Involves adsorption at the solid-liquid interface
• Surfactant that, when dissolved in water, lowers the contact angle and aids in displacing the air phase at the surface and replaces it with a liquid phase
• Excellent wetting: small contact angles

Question 9

Surfactant Application

Answer 9

• Used in emulsions
• Detergents
• Wetting agents
• Quat. ammonium surfactants adhering to bacterial cell surface to increase the leakiness of bacterial cell membranes
• Prevention of lung collapse by reducing surface tension at air-alveoli interface

Question 10

Dispersed System

Answer 10

• One phase being dispersed in another
• EX: emulsions, suspensions, aerosols
• Classified into colloidal or coarse dispersions
• Many liquid preps are dispersed systems

Question 11

Dispersed System Characteristics

Answer 11

• Large SA
• Drive to decrease surface free energy
• Tendency for aggregation or coalescence
• Unequal distribution of phases - tendency to move to top or bottom

Question 12

Coalescence

Answer 12

• Joining or merging of elements to form one mass

- Still suspended in the liquid

Question 13

Flocculation

Answer 13

• Forming fluffy, cloud like masses in liquid

- Still suspended in liquid

Question 14

Creaming

Answer 14

• Separation of an emulsion into two emulsions

- Can occur at the top of bottom of the liquid depending on density and weight of particles

Question 15

Breaking

Answer 15

• Complete separation of the two phases of the substances

- Less dense separates to the top of the container