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Questions and Answers
Which equation is used to calculate the Hydrophile-Lipophile Balance (HLB) based on the saponification and acid numbers?
Which equation is used to calculate the Hydrophile-Lipophile Balance (HLB) based on the saponification and acid numbers?
What is the first step in the Continental (dry gum) method of emulsion preparation?
What is the first step in the Continental (dry gum) method of emulsion preparation?
In the preparation of primary emulsions, which of the following proportions of components is correct for fixed oils?
In the preparation of primary emulsions, which of the following proportions of components is correct for fixed oils?
Which emulsion preparation method involves mixing gum with water to form a mucilage before adding oil?
Which emulsion preparation method involves mixing gum with water to form a mucilage before adding oil?
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What is the primary purpose of using a homogenizer in emulsion preparation?
What is the primary purpose of using a homogenizer in emulsion preparation?
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Which type of emulsifying agent is compatible with polyvalent cations?
Which type of emulsifying agent is compatible with polyvalent cations?
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What is the main characteristic of cationic surfactants?
What is the main characteristic of cationic surfactants?
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What type of emulsions do alkali soaps typically form?
What type of emulsions do alkali soaps typically form?
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Which emulsifying agent is typically produced at neutral pH and is incompatible with acids?
Which emulsifying agent is typically produced at neutral pH and is incompatible with acids?
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What differentiates microemulsions from ordinary emulsions?
What differentiates microemulsions from ordinary emulsions?
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Which emulsifying agent forms w/o emulsions and is a soap of di/trivalent metal?
Which emulsifying agent forms w/o emulsions and is a soap of di/trivalent metal?
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What is the diameter range of internal phase droplets in microemulsions?
What is the diameter range of internal phase droplets in microemulsions?
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What is the characteristic of amphoteric surfactants?
What is the characteristic of amphoteric surfactants?
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Which test can be used to identify an oil-in-water (o/w) emulsion?
Which test can be used to identify an oil-in-water (o/w) emulsion?
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Which of the following emulsifying agents is NOT known to cause toxicity or irritancy?
Which of the following emulsifying agents is NOT known to cause toxicity or irritancy?
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What characteristic of water makes it a good conductor of electricity in the conductivity test?
What characteristic of water makes it a good conductor of electricity in the conductivity test?
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What does a higher HLB value indicate about an emulsifying agent?
What does a higher HLB value indicate about an emulsifying agent?
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How do emulsifying agents prevent coalescence of droplets in emulsions?
How do emulsifying agents prevent coalescence of droplets in emulsions?
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What would you expect to observe in a w/o emulsion under UV light during the fluorescence test?
What would you expect to observe in a w/o emulsion under UV light during the fluorescence test?
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Which of the following statements about microemulsions is true?
Which of the following statements about microemulsions is true?
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What would indicate that an emulsion is w/o type using the dye-solubility test?
What would indicate that an emulsion is w/o type using the dye-solubility test?
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What is the main effect of increasing the globule size on the creaming of an emulsion?
What is the main effect of increasing the globule size on the creaming of an emulsion?
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What is coalescence in the context of emulsion stability?
What is coalescence in the context of emulsion stability?
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Which of the following factors does NOT affect the rate of creaming according to Stoke's equation?
Which of the following factors does NOT affect the rate of creaming according to Stoke's equation?
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What is a strategy to reduce the creaming phenomenon in emulsions?
What is a strategy to reduce the creaming phenomenon in emulsions?
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What happens during the process of breaking in emulsions?
What happens during the process of breaking in emulsions?
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What does an increase in viscosity of the continuous phase do to the creaming process?
What does an increase in viscosity of the continuous phase do to the creaming process?
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Which of the following describes flocculation?
Which of the following describes flocculation?
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What does an increase in particle size typically indicate in emulsion stability?
What does an increase in particle size typically indicate in emulsion stability?
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What is the purpose of antioxidants in emulsion preservation?
What is the purpose of antioxidants in emulsion preservation?
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Which method is used to determine the viscosity of emulsions?
Which method is used to determine the viscosity of emulsions?
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What change is observed in the viscosity of o/w emulsions during flocculation?
What change is observed in the viscosity of o/w emulsions during flocculation?
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What would you expect if the density of the internal phase equals the density of the external phase?
What would you expect if the density of the internal phase equals the density of the external phase?
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Which of the following tests assesses the rate of flocculation in emulsions?
Which of the following tests assesses the rate of flocculation in emulsions?
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What does cycling an emulsion between temperatures of 4°C and 45°C investigate?
What does cycling an emulsion between temperatures of 4°C and 45°C investigate?
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How does freezing impact emulsions compared to heating?
How does freezing impact emulsions compared to heating?
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What is the main effect of phase separation in emulsions?
What is the main effect of phase separation in emulsions?
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Study Notes
Microemulsions
- Microemulsions form with simple mixing of components, unlike ordinary emulsions requiring high shear conditions.
- Microemulsions appear transparent, unlike macroemulsions.
- Internal phase droplets in microemulsions range between 10-200nm.
- Microemulsions are thermodynamically stable, unlike macroemulsions.
Emulsion Types
- There are two basic types of microemulsions: oil-in-water (o/w) and water-in-oil (w/o).
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Dilution test identifies emulsion type based on external phase solubility:
- o/w emulsions dilute with water.
- w/o emulsions dilute with oil.
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Conductivity test utilizes water's conductivity, allowing it to conduct electricity more than oil.
- o/w emulsions conduct electricity better due to water's continuity.
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Dye-solubility test uses water-soluble dyes like Amaranth:
- Continuous phase appears red in o/w emulsions.
- Scattered globules appear red, and the continuous phase is colorless in w/o emulsions.
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Fluorescence test leverages oil's fluorescence under UV light:
- o/w emulsions show a spotty pattern.
- w/o emulsions fluoresce.
Emulsifying Agents
- Emulsifiers (SAA) have hydrophilic and hydrophobic parts, forming monolayers at the oil/water interface.
- They prevent globule coalescence:
- o/w emulsions form when particles prefer the aqueous phase.
- w/o emulsions form when particles prefer the oil phase.
Emulsifying Agent Classification
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Synthetic emulsifying agents:
- Form monomolecular films.
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Anionic emulsifying agents:
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Alkali soaps: Sodium, potassium, and ammonium salts of fatty acids.
- Form o/w emulsions.
- Precipitate fatty acids in acidic conditions.
- For external use.
- Incompatible with polyvalent cations.
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Soap of di/trivalent metals:
- e.g. Cal oleate.
- Promote w/o emulsions.
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Amine soaps:
- e.g. N(CH2CH2OH)3.
- Neutral pH.
- Incompatible with acids and high electrolyte concentrations.
- Produce o/w emulsions.
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Sulfated and sulfonated compounds:
- e.g. Sodium lauryl sulfate.
- Stable over high pH range.
- Form o/w emulsions.
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Alkali soaps: Sodium, potassium, and ammonium salts of fatty acids.
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Cationic surfactants:
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Quaternary ammonium compounds:
- e.g. Cetrimide, benzalkonium chloride.
- Disadvantages: toxicity, irritancy.
- Incompatible with anionic surfactants, polyvalent anions.
- Unstable at high pH.
- Marked antibacterial and anti-infective properties.
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Quaternary ammonium compounds:
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Nonionic surfactants:
- Low toxicity and irritancy, suitable for oral and parenteral administration.
- High compatibility, less sensitive to pH changes or electrolyte addition.
- e.g. Tweens (polyethylene fatty acid ester) for o/w emulsions.
- e.g. Spans (sorbitan fatty acid ester) for w/o emulsions.
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Amphoteric surfactants:
- Change charge depending on pH.
- Cationic at low pH.
- Anionic at high pH.
- e.g. Lecithin, used to stabilize intravenous fat emulsions.
- Change charge depending on pH.
Hydrophile-Lipophile Balance (HLB)
- HLB measures the hydrophilic portion's ratio to the lipophilic portion of a molecule.
- Higher HLB indicates greater hydrophilicity.
- Spans are lipophilic, with low HLB values.
- Tweens are hydrophilic, with high HLB values.
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HLB calculation:
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Griffin equation: HLB = 20 (1 – S / A)
- S: saponification number of the ester.
- A: acid number of the fatty acid.
- Davis equation: HLB = hydrophilic group number – lipophilic group number + 7.
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Griffin equation: HLB = 20 (1 – S / A)
Emulsion Preparation Methods
- Small-scale: Porcelain mortar and pestle.
- Large-scale: Mechanical stirrer, colloid mill, homogenizer.
Proportions of Oil, Water, and Gum
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Type of oil:
- Fixed oil: 4:2:1 (oil:water:gum).
- Mineral oil: 3:2:1 (oil:water:gum).
- Volatile oil: 2:2:1 (oil:water:gum).
Emulsion Preparation Methods
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Continental or dry gum method:
- Triturate emulsifier with oil in a dry mortar.
- Add water at once.
- Triturate rapidly and continuously until a thick white cream forms (primary emulsion).
- Slowly add remaining water to form the final emulsion.
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English or wet gum method:
- Triturate gum with water to form a mucilage.
- Slowly add oil in portions, triturating after each addition.
- After all oil is added, mix thoroughly to form the primary emulsion.
- Add remaining water to make the final emulsion.
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Bottle or Forbes bottle method:
- For volatile oils or low viscosity oils.
- Add gum and oil to a dry bottle.
- Shake. Add water (volume equal to oil) in portions, shaking vigorously to form the primary emulsion.
- Add remaining water to make the final emulsion.
Emulsion Stability
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Instability types:
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Flocculation and creaming:
- Flocculation: Globule clumps form, rising or settling more rapidly than individual particles.
- Creaming: Floccule concentration in an upward or downward layer depending on the internal phase density.
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Coalescence and breaking:
- Coalescence: Emulsified particles merge into larger particles.
- Breaking: Complete separation of oil and water due to coalescence and creaming.
- Phase inversion: Switching of internal and external phases.
- Miscellaneous physical and chemical changes: Changes in viscosity, color, or odor.
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Flocculation and creaming:
Creaming
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Stokes' equation factors influencing creaming:
- dx/dt = d2 (ρi-ρe)g/18η
- dx/dt: rate of settling.
- D: diameter of particles.
- ρ: density of internal and external phases.
- g: gravitational constant.
- η: viscosity of the medium.
- dx/dt = d2 (ρi-ρe)g/18η
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Factors affecting creaming:
- Globule size: Larger globules promote creaming.
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Density of internal and external phases:
- Δρ = 0: no creaming.
- Δρ = negative: upward creaming.
- Δρ = positive: downward creaming.
- Gravity: Constant, but centrifugation can be applied.
- Viscosity: Higher viscosity reduces creaming.
Strategies to Reduce Creaming
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Principle:
- Reduce droplet size.
- Reduce density difference.
- Increase continuous phase viscosity.
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Method:
- Reduce droplet size: Use a homogenizer.
- Reduce density difference: Add oils with a density greater than water (weighting agents).
- Increase viscosity: Add thickening or gelling agents, e.g., methylcellulose.
Coalescence and Breaking
- Coalescence is the merging of emulsified particles into larger particles.
- Breaking, caused by coalescence and creaming, results in complete oil separation from water.
Preservation of Emulsions
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Preservation from oxidation:
- Antioxidants prevent changes caused by atmospheric oxygen, such as rancidity.
- Examples: Butylated hydroxyanisole (BHA), Butylated hydroxytoluene (BHT).
Quality Control Tests for Emulsions
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Particle size and particle count determination:
- Performed using optical microscopy and Coulter counter apparatus.
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Viscosity determination:
- Assesses changes during aging.
- Cone and plate viscometers are used.
- Flocculation in o/w emulsions increases viscosity initially.
- Flocculation in w/o emulsions decreases viscosity initially, stabilizing later.
- Decreased viscosity with age indicates increased particle size due to coalescence.
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Phase separation determination:
- Visual observation or measurement of separated phase volumes.
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Electrophoretic properties determination:
- Assesses flocculation since electrical charges on particles influence flocculation rate.
- o/w emulsions with fine particles exhibit low resistance, while increased resistance indicates aggregation and instability.
Assessment of Emulsion Shelf Life
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Stress conditions:
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Aging and temperature:
- Cycling between 4°C and 45°C accelerates coalescence and creaming, affecting viscosity.
- Temperature affects consistency: thin at elevated temperatures, thick at room temperature.
- Freezing damages emulsions more than heating due to emulsifier solubility sensitivity.
- Centrifugation: Accelerates creaming and sedimentation.
- Light exposure: Can cause oxidation and color changes.
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Aging and temperature:
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Description
This quiz explores the fascinating world of microemulsions, focusing on their formation, characteristics, and the different types like oil-in-water and water-in-oil. It also discusses various tests used to identify emulsion types, enhancing understanding of this unique topic in chemistry.
