dispersion B

What is an emulsion?

An emulsion is a mixture of two immiscible liquids in which one liquid is dispersed as small droplets throughout the other.

Remember: Immiscible means two liquids do not mix or dissolve in each other. For example, oil and water.

What is an emulsifying agent?

emulsions often contain an emulsifying agent.

An emulsifying agent is an excipient that helps stabilize the emulsion by preventing oil and water droplets from easily separating.

It works by helping reduce the interfacial tension between the two liquids.

multiple emersions possible

complicated emulsions:

• o/w/o: Oil-in-water-in-oil

• w/o/w: Water-in-oil-in-water

Routes of administration for emulsions

Route	Explanation
Oral	Taken by mouth; usually o/w
Topical	Applied to skin; can be o/w or w/o
Parenteral	Administered by injection
Ophthalmic	Used in the eye

most emulsions are topical. medication is usually found in the internal (dispersed) phase.

what are 3 problems in a emulsion

1. Creaming

2. Cracking

3. Phase inversion

what is creaming

when internal phase droplets merge and
separate from the continuous phase
After creaming has occurred can re-disperse with
shaking

what is Cracking

Cracking occurs when dispersed droplets coalesce (join together), causing the emulsion to separate into distinct liquid phases.

what is Phase inversion

Phase inversion occurs when an emulsion switches from oil-in-water (o/w) to water-in-oil (w/o), or vice versa.

Emulsions can be stabilized through use of? (4)

1) Natural emulsifiers
2) Synthetic surfactants
3) Hydrocolloids
4) Solid particles

What is acacia?

Acacia is a natural emulsifying agent obtained from the Acacia senegal tree.

It is also known as Gum Arabic.

In pharmacy, acacia helps stabilize emulsions, particularly oil-in-water (o/w) emulsions.

What is a surfactant?

A surfactant is a molecule containing both a hydrophilic and a lipophilic portion.

• Hydrophilic: Attracted to water.

• Lipophilic: Attracted to oil or fats.

. How do surfactants work?

• Concentrate at the oil–water interface: Their water-loving portions face water, while their oil-loving portions interact with oil.

• Reduce interfacial tension: This decreases the resistance to forming an interface between oil and water.

• Help form smaller droplets: Lower interfacial tension makes it easier to break large oil globules into smaller droplets.

Surfactants can also help prevent these droplets from merging again.

Three types of synthetic surfactants

Type	Charge	Examples from lecture
Anionic	Negative (−)	Sodium docusate, sodium oleate
Nonionic	No net ionic charge	Spans and Tweens
Cationic	Positive (+)	Quaternary ammonium halides

Acacia vs. synthetic surfactants

Acacia	Synthetic surfactants
Natural emulsifier	Manufactured emulsifying agents
Derived from Acacia senegal	Examples include Spans and Tweens
Can form a protective layer around droplets	Concentrate at oil–water interface
Helps prevent droplets from combining	Reduce interfacial tension and stabilize droplets

what are Hydrocolloids

Hydrocolloids are substances that interact with water and help stabilize emulsions by forming protective layers around dispersed droplets.

how do they work

1. May provide a charge which causes droplets to repel each other

2. May swell to increase viscosity of system

3. Hydrocolloids may be natural (gelatin), semi-
   synthetic (methylcellulose) or synthetic (Carbopol)

How do solid particles stabilize emulsions?

Tend to form layer around droplet and swell Increases viscosity and reduces attraction between droplets

Examples of solid particle emulsifiers

• Bentonite

• Aluminum hydroxide

• Magnesium trisilicate

What is an auxiliary agent?

An auxiliary agent is an ingredient added to help stabilize an emulsion by increasing its viscosity (thickness).

• Auxiliary agents cannot form an emulsion by themselves. They must work alongside a primary emulsifying agent.

ex of auxilary agent

Examples: fatty acids (stearic acid), fatty alcohols
(cetyl alcohol) and fatty esters (glyceryl
monostearate)

How do auxiliary agents work?

Remember that emulsions contain droplets of one liquid dispersed in another liquid.

• When viscosity is low, droplets can move around more easily.

• When viscosity increases, droplets move more slowly.

• Slower movement reduces how frequently droplets collide, helping prevent separation.

Higher viscosity → Slower droplet movement → Improved emulsion stability.

Advantages of Emulsions

1. Liquid dosage form, good alternative to tablets and capsules

2. Undesirable taste in the internal phase can be
   masked

3. Aqueous phase can be flavored

4. Sustained and controlled drug delivery

5. Improved drug stability

Disadvantages of emulsions

1. Physical instability, phases tend to separate. Need to shake before use to ensure redispersion

2. Accuracy need to measure the dose

3. Storage condition may affect stability

4. Microbial contamination can lead to cracking (need for preservation)

5. Bulky dosage form, difficult to transport

what is Hydrophilic-Lipophilic Balance (HLB),

helps pharmacists choose the correct emulsifying agent when preparing emulsions.

what does and low and high HLB mean

Low HLB = Oil-loving → indicate emulsifier is oil-soluble so oil phase will pre-dominate and form a w/o emulsion

High HLB = Water-loving → Oil-in-water (o/w) emulsion

hlb value range

How are emulsions prepared?

Energy must be put into the system to break one liquid into small droplets and disperse them throughout the other.

three techniques help

name the techniques

Technique	Simple explanation
Homogenization	Uses mechanical force to break large droplets into smaller, more uniform droplets
High-speed shear	Uses rapid mixing and strong shear forces to break up droplets
Trituration	Uses grinding and mixing with a mortar and pestle to help form an emulsion

Four methods of extemporaneous preparation used to compound emulsions.

1. Continental method

2. English method

3. Bottle method

4. Beaker method

what is continental/dry gum method

Also called the dry gum method.

• The emulsifying agent (such as acacia) is initially mixed with oil.

• Water is then incorporated to form the primary emulsion.

Dry Gum Method = Gum + Oil first → Add water all at once → Triturate vigorously.

what ratio is used for dry gum method and list the prepartion proess

from oil (4 parts), water (2 parts), hydrocolloid or gum emulsifier (1 part)

what is English method

Also called the wet gum method.

• The emulsifying agent is initially mixed with water.

• Oil is gradually incorporated to form the primary emulsion.

what ratio is ingrediants for wet gum method and how is it perfomed

:2:1 = Oil : Water : Gum

what is Bottle method

Also called the Forbes method.

• Ingredients are mixed by shaking them in a bottle.

• Works best if oil has low viscosity

what proportion does bottle method use and what order does it go in

Same proportions of oil, water and gum (4:2:1)

what is Beaker method

Unlike the Continental, English, and Bottle methods, the Beaker Method commonly uses synthetic surfactants instead of gum emulsifiers such as acacia. approximately 5% synthetic surfactant is typically needed.

How is the Beaker Method performed?

always add the internal phase to the external phase in the Beaker Method,

What is a colloidal dispersion?

A colloidal dispersion is a mixture containing extremely small particles dispersed throughout another substance.

colloidal particles range from: 1 nm to 1 μm

char of colloidal dispersion

how do you Classifiy colloids

• Lyophilic colloids: Have an affinity for the dispersion medium.

• Lyophobic colloids: Have little affinity for the dispersion medium.

why do colloids carry a surface charge

May carry a surface charge depending on pH of system and chemical functional groups of colloid

Charge keeps particles separated

Why are hydrophobic colloids less stable?

Hydrophobic colloids have little affinity for water.

Because they interact poorly with the surrounding aqueous phase:

• They are less easily stabilized by hydration.

• Particles have a greater tendency to associate with one another.

• This association may cause aggregation and phase separation.

This makes hydrophobic colloids generally less stable than hydrophilic colloids in water.

How can hydrophobic colloids be stabilized?

1. Add surfactants - Surfactants can adsorb onto the particle surface and improve its interaction with the surrounding liquid.

2. Add protective colloids - Protective colloids, such as gelatin, can coat the hydrophobic particles.

How can hydrophobic colloids remain dispersed

some hydrophobic colloids can:

• Carry an electrical charge on their surfaces.

• Adsorb ions from the surrounding solution.

Some hydrophobic colloids may also carry a charge or adsorb ions from the solution Mutual repulsive forces and Brownian movement then keep colloid dispersed

What role does Brownian movement play?

Brownian movement is the random movement of very small particles caused by collisions with surrounding liquid molecules.

Because colloidal particles are extremely small, Brownian movement helps keep them dispersed and counteracts settling.

Together, surface charge and Brownian movement help maintain colloidal stability.

What happens when electrolytes are added?

Electrolytes produce ions in solution.

1. Addition of electrolyte may neutralize charge
   and cause settling

What are gels?

A gel is a thick, jelly-like preparation formed by a network of molecules that traps liquid and prevents it from flowing freely.

• Hydrophilic: Attracted to water.

• Colloidal system: Contains very small dispersed particles or large molecules.

• Cross-linking: Molecules connect together to form a 3D network.

• High viscosity: The gel is thick and does not flow easily.

• Gelling agent (0.5–2%): Ingredient that helps create the thick gel structure.

Main idea: The 3D network restricts movement of the liquid, making the gel thick.

Single-phase vs. two-phase gels

Single-phase gels

Single-phase gels contain large organic macromolecules uniformly distributed throughout the liquid, with no apparent boundaries between dispersed and continuous phases.

two-phase gels

Two-phase gels contain discrete solid particles dispersed within the gel matrix.

What are jellies?

What is the main problem when preparing gels?

wetting of the gelling agent as a major problem.

When dry gelling powder is added to water, its outer surface may hydrate rapidly.

This can create lumps with a hydrated outer layer and dry powder trapped inside.

Result: The lumps become difficult to disperse and hydrate completely.

How do we prevent lumps?

1. add powder gradually

2. Pre-disperse in a nonsolvent

3. Levigation

how can adding powder gradually help

• Add the gelling agent in small portions.

• Mix vigorously during addition.

• This helps distribute the powder before lumps form.

how can Pre-disperse in a nonsolvent help

• First disperse the powder in a compatible liquid in which it is insoluble.

• Then add the dispersion to the appropriate solvent with mixing.

• This helps prevent the powder from clumping immediately.

what do Many gelling agents include

Alginic acid
Bentonite or Vee Gum (magnesium aluminum silicate)
Carbomer (Carbopol) – alcohol compatible
Poloxamer (15-50% concentration)

what are some food items that are emulsions

1. milk is an oil in\ water emulsion

2. margarine is a water in oil emulsion

3. ice cream is an oil and air in water emulsion

4. Other food emulsions include mayonnaise, salad dressings

Use of emulsion disperse systems

Useful for topical, oral, ophthalmic and parenteral
(injectable) dose forms. To be shaken before use