Pharmaceutics: Emulsions to Suspensions

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the significance of controlling polymer concentration in a deflocculated system?

It affects the ease of sedimentation.

It affects the particle size distribution.

It influences the stability of the suspension. (correct)

It determines the viscosity of the suspension.

Which of the following is NOT a property ideally exhibited by a suspension?

Redispersibility

Pourability

High viscosity (correct)

Homogeneity

What does a higher sedimentation volume ratio (F) indicate?

A higher final volume of sediment.

A larger total volume of suspension.

A more stable suspension. (correct)

A less dense sediment layer.

In the context of thixotropy, what behavior is desirable when shaking the suspension?

The suspension should flow freely and thin out. Signup and view all the answers

Which factor is essential to evaluate when assessing the quality of a suspension?

The particle size analysis. Signup and view all the answers

What is the primary disadvantage of caking in a suspension?

It cannot be eliminated by size reduction. Signup and view all the answers

Which characteristic of a suspension does not contribute to the effectiveness of taste-masking?

Suspension in solution Signup and view all the answers

What is the intended outcome when using flocculating agents in a suspension?

To minimize caking Signup and view all the answers

Which type of suspension is classified by its dispersion medium?

Aqueous or oily suspensions Signup and view all the answers

What particle size in a suspension is likely to cause irritation if injected?

Greater than 5 μm Signup and view all the answers

What characteristic is desirable in solid drug particles used in suspensions?

Narrow size range Signup and view all the answers

Which of the following issues does NOT result from large particles in a suspension?

Improved drug release rate Signup and view all the answers

What is the primary goal of size reduction in drug suspension formulation?

To facilitate easier dispersion in the medium Signup and view all the answers

What signifies a system's stability with respect to colloidal systems?

Having a higher Zeta potential than ±30 mv Signup and view all the answers

What is the effect of increasing droplet size in an emulsion?

Decreases stability, leading to flocculation Signup and view all the answers

What factors influence the rheological properties of emulsions?

Phase volume ratio and continuous phase characteristics Signup and view all the answers

In an O/W emulsion, how can viscosity be increased?

By adding thickening agents like gums Signup and view all the answers

What characteristic of emulsions is indicated by thixotropy?

Increased viscosity at rest and decreased viscosity under stress Signup and view all the answers

What is the purpose of having emulsions formulated with appropriate shear thinning properties?

To ensure easy application and stability during use Signup and view all the answers

What characterizes the dispersed particles in an emulsion?

They do not dissolve but are suspended. Signup and view all the answers

How does the consistency of a low internal phase volume emulsion compare to that of its continuous phase?

It maintains the same consistency as the continuous phase Signup and view all the answers

What role does Zeta potential play in preventing coalescence in colloidal systems?

It enhances the repulsive forces between particles. Signup and view all the answers

What does the term 'emulsion stability' refer to?

The time an emulsion remains mixed before separating. Signup and view all the answers

Which of the following best explains why creating an emulsion requires energy?

To overcome interfacial tension and create surface area. Signup and view all the answers

What happens to the system when water and oil in an emulsion separate?

The emulsion is lost and no longer exists. Signup and view all the answers

What is the relationship between surface area and emulsification?

Increasing surface area is necessary for successful emulsification. Signup and view all the answers

Which of the following statements about the phases in an emulsion is correct?

The internal phase can vary in the type of matter dispersed. Signup and view all the answers

What is the primary role of energy input in the emulsification process?

To disrupt the bulk liquids and form fine droplets Signup and view all the answers

What occurs during the creaming process in an oil-in-water emulsion?

Dispersed particles rise to the surface to form a layer Signup and view all the answers

Why are emulsifiers important in emulsions?

They help to reduce the energy required for emulsification. Signup and view all the answers

Which of the following statements about sedimentation is correct?

Sedimentation results in discrete entities settling at the bottom due to higher density Signup and view all the answers

What does thermodynamic instability in emulsions signify?

The need to increase surface area is always significant. Signup and view all the answers

Which method can help reduce both creaming and sedimentation in emulsions?

Adding viscosity modifiers to thicken the external phase Signup and view all the answers

What does the equation W = γ_AB * ΔA signify in emulsification?

It calculates the energy required for droplet formation Signup and view all the answers

Which of the following processes are considered components of kinetic instability in emulsions?

Creaming and sedimentation Signup and view all the answers

What factor directly contributes to the differences in density that cause creaming and sedimentation?

The inherent density differences between phases Signup and view all the answers

How can emulsions be restored after creaming occurs?

By agitating or shaking the emulsion before use Signup and view all the answers

Which statement accurately describes the effect of a wetting agent on drug particles?

It reduces surface tension, facilitating easier dispersion of solid particles. Signup and view all the answers

What is the primary role of controlled flocculation in a suspension?

To prevent particles from forming a solid cake. Signup and view all the answers

Which of the following is NOT a flocculating agent?

Bicarbonate Signup and view all the answers

What effect does increasing the viscosity (η) of the liquid phase have on sedimentation?

It decreases the rate of sedimentation. Signup and view all the answers

Which of the following should be avoided to prevent poor pourability in suspensions?

Very high viscosity Signup and view all the answers

What happens to the sedimentation velocity (V) if the density of the liquid increases?

It decreases. Signup and view all the answers

Which agent acts as a viscosity-enhancing agent in suspensions?

Sodium carboxymethylcellulose Signup and view all the answers

Which of the following is a characteristic of surfactants used in formulations?

They lower the contact angle for hydrophilic surfaces. Signup and view all the answers

Study Notes

Emulsions and Creams

Emulsions are disperse systems, with low viscosity resistance. They are either oil-in-water (O/W) or water-in-oil (W/O), which are often unstable thermodynamically. Emulsifiers are used to stabilize them.
An emulsion is a colloid, where one liquid is dispersed in another. The dispersed substance is the internal phase, and the continuous substance is the external phase. The size of dispersed particles is between 1 and 1000 nanometers (nm).
Instability results from surface area and interfacial tension, which requires energy to create.

Instability of Emulsions

Emulsions are thermodynamically unstable due to high surface area between immiscible phases. This causes an increase in energy (positive ΔA).
Reducing the interfacial tension and increasing surface area together, represents the energy needed for emulsion creation (work).

Kinetic Instability

Creaming and sedimentation are vertical processes. Creaming occurs when dispersed particles are less dense than the continuous phase, making them rise. Sedimentation is when denser particles settle.
Stokes' law describes the velocity of sedimentation, dependent on particle radius, difference in density and viscosity of the continuous phase.
Factors affecting instability include particle size, density differences, and viscosity of the continuous phase. Smaller particle sizes and higher viscosities reduce instability.

Stabilizing Methods - Emulsifiers

Emulsifiers, also known as surfactants, are surface-active agents.
They migrate to the interface between phases, reducing interfacial tension and preventing coalescence and flocculation.
Lowering interfacial tension improves emulsion stability and reduces tendency to form larger droplets (coalesce.)
Creating repulsive forces between dispersed particles also increases stability.
An increase in surface tension and increase in viscosity cause flocculation to occur.

Zeta Potential

Zeta potential is a measure of the repulsive forces between particles in a colloidal system. A higher zeta potential corresponds to greater stability.
Emulsions with a higher zeta potential are more stable against coalescence and flocculation due to higher repulsive forces.

Emulsion Rheology

Viscosity of an emulsion (η) is often dependent on the volume fraction of the internal phase (ϕ) . Eq. η = η₀(1 + 2.5φ) shows relationship.

Factors affecting Emulsion Type

Bancroft's rule states that the liquid in which the emulsifier is more soluble will become the continuous phase of the emulsion.
HLB numbers of surfactants indicate their hydrophilic-lipophilic balance and influence the type of emulsion (o/w greater HLB).

Creams

Creams are semisolid emulsions, typically oil-in-water (o/w) emulsions.
They are formulated for topical application and have properties like ease of spreading, and non-greasy feel.
Creams contain emulsifiers, and other components to maintain the required texture and properties.

Colloids and Suspensions

Colloids and suspensions are dispersions of small particles in a continuous medium.
Colloidal particles are typically between 1 nm and 1 µm in size.
Lyophobic colloids tend to be unstable, while lyophilic colloids are more stable.
Colloidal dispersions can be classified by the physical state of the dispersed phase and medium.

Quality Control

Physical appearance, ease of redispersal, and homogeneity are important quality control factors for preparing flocculated emulsions.
Rheological properties are crucial for stability during storage and use.

Flocculation and Deflocculation

Flocculation, when particles aggregate together (a loose cluster), will influence the consistency.
Deflocculation describes particles remaining independent and separate.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz explores the essential properties and behaviors of suspensions in pharmaceutics. You will learn about sedimentation, thixotropy, flocculation, and the implications of particle size. Test your knowledge on critical factors that influence the quality and effectiveness of drug suspensions.